JAVA_VR23_OOPS THROUGH JAVA PPT UNIT-1.pptx

oops with java

1. OOPS THROUGH JAVA

2. UNIT-I 2

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5. OS/Hardware machine code C source code myprog.c gcc myprog.exe Platform Dependent JVM bytecode Java source code myprog.java javac myprog.class OS/Hardware Platform Independent 5

6. Issues: Portability Platform Independence Security Reliability Reusability / Extensibility Shareability ( Networking) 6

7. Different Programming Paradigms Functional/Procedural P rogramming/Procedure Oriented Programming) (POP) Program is a list of instructions to the computer. Procedural programming is about writing procedures or methods that perform operations on the data . Object-oriented programming (OOP) Program is composed of a collection objects that communicate with each other. While object-oriented programming is about creating objects that contain both data and methods. 7

8. Software Design Approaches: Top down vs bottom up: 8

9. Hierarchy of programming paradigms: 9

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11. PROCEDURE ORIENTED PROGRAMMING 11

12. POP VS OOP: 12

13. Pop : advantages vs disadvantages Advantages: Its relative simplicity, and ease of implementation of compilers and interpreters The ability to re-use the same code at different places in the program without copying it. An easier way to keep track of program flow. The ability to be strongly modular or structured. Needs only less memory . Disadvantages: Data is exposed to whole program, so no security for data. Difficult to relate with real world objects. Difficult to create new data types reduces extensibility. Importance is given to the operation on data rather than the data. 13 13

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15. Object-oriented programming - advantages Object-oriented programming has several advantages over procedural programming : OOP is faster and easier to execute (w.r.t Program Development) OOP provides a clear structure for the programs OOP helps to keep the Java code DRY "Don't Repeat Yourself", and makes the code easier to maintain, modify and debug OOP makes it possible to create full reusable applications with less code and shorter development time ( WORA – Write Once Run Any where) 15

16. Object-oriented programming - advantages Simplicity : Software objects model real world objects, so the complexity is reduced and the program structure is very clear. Modularity : Each object forms a separate entity whose internal workings are decoupled from other parts of the system. Modifiability : It is easy to make minor changes in the data representation or the procedures in an OO program. Changes inside a class do not affect any other part of a program, since the only public interface that the external world has to a class is through the use of methods. Extensibility : Adding new features or responding to changing operating environments can be solved by introducing a few new objects and modifying some existing ones. Maintainability : Objects can be maintained separately, making locating and fixing problems easier. Reusability : Objects can be reused in different programs. 16

17. Disadvantages of oop : Designing a program in OOP concept is a little bit tricky. The programmer should have a proper planning before designing a program using OOP approach. Since everything is treated as objects in OOP, the programmers need proper skill such as design skills, programming skills, thinking in terms of objects etc. The size of programmes developed with OOP is larger than the procedural approach. Since larger in size, that means more instruction to be executed, which results in the slower execution of programmes. 17

18. Oop (s) - concepts OOP stands for  Object-Oriented Programming . There are four main OOP concepts A bstraction ,  Encapsulation ,  Inheritance , and Polymorphism 18

19. abstraction Abstraction  is the process of hiding certain details and showing only essential information to the user . ( What is to be done ? Rather than how it is done ? ) Abstraction means using simple things to represent complexity. For eg : 1) We all know how to turn the TV on, but we don’t need to know how it works (Internal Circuit /Components ). 2) Use ATM 19

20. What are Classes and Objects ? Classes and objects are the two main aspects of object-oriented programming . class is a template for objects (i.e., collection of objects of same type) and an object is an instance of a class. 20

21. encapsulation A way to achieve Abstraction & provides “ data hiding ”. Encapsulation , is to make sure that " sensitive " data is hidden from users. Encapsulation is the practice of keeping fields within a class private, then providing access to them via public methods. It’s a protective barrier that keeps the data and code safe within the class itself. This way, we can re-use objects like code components or variables without allowing open access to the data system-wide . 21

22. inheritance It  is a mechanism in which one object acquires all the properties and behaviours of a parent object. It is an important part of OOPs (Object Oriented programming system). The idea behind  inheritance in Java  is that you can create new classes that are built upon existing classes . Inheritance supports the concept of “ reusability ”, i.e. when we want to create a new class and there is already a class that includes some of the code that we want, we can derive our new class from the existing class.  22

23. polymorphism The word polymorphism means having many forms.  The word “poly” means many and “morphs” means forms, So it means many forms. The same word to mean different things in different contexts. One form of polymorphism in Java is  method overloading . That’s when different meanings are implied by the code itself. The other form is  method overriding .  Ex: A person at the same time can have different characteristic. Like a man at the same time is a father, a husband, an employee. So the same person posses different behaviour in different situations.  23

24. In real life - oops 24

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27. What Is java ? Java is a popular Internet programming language, created in 1995. It is owned by Oracle (Previously owned by Sun Micro Systems) , and more than  3 billion  devices run Java. It is used for: Mobile applications (specially Android apps) Desktop applications Web applications Web servers and A pplication servers Games Database connection And much, much more! 27

28. Why Java ? Java is one of the most popular and widely used programming language and platform. A platform is an environment that helps to develop and run programs written in any programming language. Java is fast, reliable and secure . From desktop to web applications, scientific supercomputers to gaming consoles, cell phones to the Internet, Java is used in every nook and corner. 28

29. History of java James  Arthur  Gosling , ( born May 19, 1955) is a Canadian computer scientist, best known as the founder and lead designer behind the Java programming language . Java  was started as a project called "Oak" by James Gosling in June 1991 at Sun at Microsystems of USA. The   language  was initially called Oak after an oak tree that stood outside Gosling's office. Later the project went by the  name   Green and was finally renamed  Java , from  Java  coffee. " Java " being used as slang for "coffee" Gosling designed  Java  with a C/C++-style syntax that system and application programmers would find familiar. The first public implementation was  Java  1.0 in 1995. 29

30. JAVA VERSIONS JDK Alpha and Beta (1995) JDK 1.0 (23rd Jan 1996) JDK 1.1 (19th Feb 1997) J2SE 1.2 (8th Dec 1998) J2SE 1.3 (8th May 2000) J2SE 1.4 (6th Feb 2002) J2SE 5.0 (30th Sep 2004 ) Java SE 6 (11th Dec 2006) Java SE 7 (28th July 2011) Java SE 8 (18th March 2014) Java SE 9 (21st Sep 2017) Java SE 10 (20th March 2018) 30

31. Java Editions/platforms 31

32. Features of java (Buzz words) Simple Secured Object Oriented Robust Platform Independence ( Architecture Neutral Portable Compiled & Interpreted Multithreaded Dynamic Distributed High Performance(JIT) Java is case-sensitive 32

33. Java environment The programming environment of Java consists of three components mainly : JDK JRE JVM 33

34. JDK & JAVA API: JDK = JAVA DEVELOPMENT KIT JDK = JAVA TOOLS + JAVA API 34

35. JAVA TOOLS java api javac java javadoc javah javap jdb appletviewer 35 Packages Classes / Interfaces methods

36. Java api packages: API : Application Programming Interface Standalone Application Programming j ava.lang java.util java.io Applets / GUI & Network Programming java.net java.applet 36

37. jdk vs jre vs jvm JDK (Java Development Kit ): JDK contains everything that will be required to  develop and run  Java application. JRE (Java Runtime Environment ): JRE contains everything required to  run  Java application which has already been compiled. It doesn’t contain the code library required to develop Java application. JVM (Java Virtual Machine ): JVM is a virtual machine which works on top of your operating system to provide a recommended environment for your compiled Java code. JVM only works with bytecode . Hence you need to compile your Java application(.java) so that it can be converted to  bytecode format (also known as the .class file). Which then will be used by JVM to run an application. JVM only provide the environment needed to executed Java Bytecode . 37

38. Java virtual machine (JVM) The Java Language is a language specification. The Sun JVM is  written  in C, JVM run on your machine is a platform-dependent executable code. The  Java Virtual Machine  by Oracle, i.e., Oracle JVM( HotSpot ) on which Java Code is executed is written in C ++. 38

39. Java Virtual Machine JVM is a engine that provides runtime environment to drive the Java Code or applications. It converts Java bytecode into machines language. JVM is a part of JRE(Java Run Environment). It stands for Java Virtual Machine In other programming languages, the compiler produces machine code for a particular system. However, Java compiler produces code for a Virtual Machine known as Java Virtual Machine. First, Java code is complied into bytecode . This bytecode gets interpreted on different machines Between host system and Java source, Bytecode is an intermediary language. JVM is responsible for allocating memory space . 39

40. Java Virtual Machine 40

41. Java is both compiled &interpreted language A  compiler  is a program which converts a program from one level of language to another. Example conversion of C++ program into machine code. The java compiler converts high-level java code into bytecode (which is also a type of machine code). An  interpreter  is a program which converts a program at one level to another programming language at the  same level.  Example conversion of Java program into C++ In Java, the Just In Time Code generator converts the bytecode into the native machine code which are at the same programming levels. Hence, Java is both compiled as well as interpreted language . JIT or Just-in-time compiler is the part of the Java Virtual Machine (JVM). It is used to speed up the execution time In comparison to other compiler machines, Java may be slow in execution. 41

42. Java portability Java Source Code (Written by Developer) ( Machine Neutral ) Compiled Code / Byte Code ( Machine Neutral ) Byte Code Interpreted & executed (Executed by JVM) ( Machine Specific ) c 42

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44. Java BYTECODE Java bytecode is a compiled code of a Java program or we can say it is a set of instructions for JVM . It can execute on any platform which has a Java installation. After compilation, the Java code is converted into .class file which is also known as B ytecode /Intermediate Code . Java code is machine independent because of the JVM(Java virtual machine) that runs the bytecode in the processor. (But JVM is Machine Dependent) Also Java programmer doesn’t require knowledge about the specific OS and processors where the program will run because JVM takes care of those. 44

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46. Java execution is slower ? ? ? 46

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50. Java basics: Where to download Java. How to install Java. Setting up the Environment Variables. Our First Java Program. How to compile a Java application. How to run a Java Application. Difference between important terms in Java (JDK vs JRE or J2SE vs J2EE ..). 50

51. How to Download Java The latest version of Java can be downloaded from  Java Website URL: https://www.oracle.com/technetwork/java/javase/downloads/jdk8-downloads-2133151.html 51

52. Java Installation There are no special requirements when installing Java.  Be sure that you have suitable permissions on your computer to install software. It can be installed like any other software ( .exe ) 52

53. Setting up the Environment Variables You need to set PATH to compile Java source code and create  Java class files .   JDK bin directory contains javac and java  commands to compile and run Java programs. CLASSPATH is little different than Path and it's used by JVM rather than Operating System to load classes at runtime.  JAVA_HOME : This environment variable will point to the location of the Java home directory . ( C:\Program Files\Java\jdk1.6.0_02) Note: PATH/JAVA_HOME is for OS and CLASSPATH is for JVM PATH/JAVA_HOME : C:\Program Files\Java\jdk1.8.0_51\bin (Tools) CLASSPATH: C:\Program Files\Java\jdk1.8.0_51\lib ( Supporting files – jars ) 53

54. Sample Java program ( MyClass.java ) import java.lang.*; public class MyClass { public static void main ( String [] args ) { System . out . println ( "Welcome to Java World!" ); } } 54

55. Java main() method 55

56. Structure of Java Program Documentation Section - Suggestion Package Section - Optional Import Section - Optional Interface Section - Optional Class Definition(s) - Required / optional Main method class - Essential 56

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58. Java comments (Documentation) // Single-Line Comment /* * Multiple-Line comment */ /** * JavaDoc comment */ 58

59. Java tools/ide: 1) To compile a java program: Use javac Example: C :\Users\Rollno> javac MyClass.java 2) To run a java program: Use java Example: C:\ Users\Rollno> java MyClass 59

60. Java Programming Basics – data types Two categories: Primitive (Fundamental) List shown in next slide Non-Primitive ( Referenced – Group of values / Advanced data types) Class Interface String Array etc., 60

61. Data types: 61

62. Java keywords abstract boolean break byte byvalue case cast * catch char class const * continue default do double else extends false # final finally float for future * generic * goto * if implements import inner * instanceof int interface long native new null # operator * outer * package private protected public rest * return short static super switch synchronized this threadsafe * throw throws transient true # try var * void volatile while 62 Note : Total 60=33 (exists)+27 new keywords & some( *) are reserved for future purpose, # - defined by java

63. java primitive data types 63 Default Value 0.0 0.0 \u0000 false

64. Java coding( naming ) conventions - standards : For good maintenance and readability of code in java 64

65. Java coding( naming ) conventions - standards : 65 For example : package java.lang ; package lbrce.cse ; package lbrce.ece ; For example : RED , YELLOW,GREEN MAX_PRIORITY , MAX_MARKS RED , YELLOW , MAX_PRIORITY , MAX_STOCK_COUNT

66. Variables – types: A variable is a name given to a memory location. It is the basic unit of storage in a program. The value stored in a variable can be changed during program execution. A variable is only a name given to a memory location, all the operations done on the variable effects that memory location. In Java, all the variables must be declared before use . 66

67. How to declare variables? We can declare variables in java as follows: 67

68. types of variables in Java: There are three types of variables in Java: Local Variables Instance Variables Static Variables 68

69. 1) Local Variables DEF : A variable defined within a block or method or constructor is called local variable . These variable are created when the block in entered or the function is called and destroyed after exiting from the block or when the call returns from the function. The scope of these variables exists only within the block in which the variable is declared. i.e. we can access these variable only within that block. Initialization of Local Variable is Mandatory. 69

70. EXAMPLE: public void StudentAge() { // local variable age int age = 0; age = age + 5; } 70

71. 2) Instance Variables DEF : Instance variables are non-static variables and are declared in a class outside any method, constructor or block . As instance variables are declared in a class, these variables are created when an object of the class is created and destroyed when the object is destroyed. Unlike local variables, we may use access specifiers for instance variables. If we do not specify any access specifier then the default access specifier will be used. Initialization of Instance Variable is not Mandatory. Its default value is 0 Instance Variable can be accessed only by creating objects. 71

72. EXAMPLE: class Marks { // These variables are instance variables. // These variables are in a class // and are not inside any function int engMarks ; int mathsMarks ; int phyMarks ; } 72

73. 3)Static Variables DEF : Static variables are also known as Class variables . These variables are declared similarly as instance variables, the difference is that static variables are declared using the static keyword within a class outside any method constructor or block. Unlike instance variables, we can only have one copy of a static variable per class irrespective of how many objects we create. Static variables are created at the start of program execution and destroyed automatically when execution ends. Initialization of Static Variable is not Mandatory. Its default value is 73

74. EXAMPLE: class Emp { // static variable salary public static double salary; } For Accessing Static Variable: Emp.salary 74

75. Java operators: Operator  in java is a symbol that is used to perform operations. For example : +, -, *, / etc . 75

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77. Relational operators: Operator Meaning == Is equal to != Is not equal to > Greater than < Less than >= Greater than or equal to <= Less than or equal to 77

78. Logical operators: Operator Meaning Work && Logical AND If both operands are true then only "logical AND operator" evaluate true. || Logical OR The logical OR operator is only evaluated as true when one of its operands evaluates true. If either or both expressions evaluate to true, then the result is true. ! Logical Not Logical NOT is a Unary Operator, it operates on single operands. It reverses the value of operands, if the value is true, then it gives false, and if it is false, then it gives true. 78

79. Assignment operators: The Java Assignment Operators are used when you want to assign a value to the expression.  The assignment operator denoted by the single equal sign  = Example : int a = 6; float b = 6.8F; 79

80. Java Compound Assignment Operators : Java provides some special Compound Assignment Operators, also known as Shorthand Assignment Operators. It's called shorthand because it provides a short way to assign an expression to a variable . For example, you write a statement: a = a+6; In Java, you can also write the above statement like this: a += 6; 80

81. unary arithmetic operators: In Java, unary arithmetic operators are used to increasing or decreasing the value of an operand.  Increment operator adds 1 to the value of a variable, whereas the decrement operator decreases a value . 81 Example Description val = a++; Store the value of "a" in "val" then increments. val = a--; Store the value of "a" in "val" then decrements. val = ++a; Increments "a" then store the new value of "a" in " val ". val = --a; Decrements "a" then store the new value of "a" in " val ".

82. Bitwise operators in Java Bitwise operators are used to perform manipulation of individual bits of a number . Bitwise OR (|)  Bitwise AND (&) Bitwise XOR (^)  Bitwise Complement (~) Shift Operators : Signed Right shift operator (>>)  , Left shift operator (<<), Unsigned Right shift operator (>>>)  82

83. Bitwise OR (|)  a = 5 = 0101 (In Binary) b = 7 = 0111 (In Binary) Bitwise OR Operation of 5 and 7 0101 | 0111 ________ 0111 = 7 (In decimal) 83

84. Bitwise AND (&) a = 5 = 0101 (In Binary) b = 7 = 0111 (In Binary) Bitwise AND Operation of 5 and 7 0101 & 0111 ________ 0101 = 5 (In decimal) 84

85. Bitwise XOR (^)  a = 5 = 0101 (In Binary) b = 7 = 0111 (In Binary) Bitwise XOR Operation of 5 and 7 0101 ^ 0111 ________ 0010 = 2 (In decimal) 85

86. Bitwise Complement (~)  a = 5 = 0101 (In Binary) Bitwise Compliment Operation of 5 ~ 0101 _______ 1010 = 10 (In decimal) Note:  Compiler will give 2’s complement of that number, i.e., 2’s compliment of 10 will be -6. 86

87. Shift Operators: These operators are used to shift the bits of a number left or right thereby multiplying or dividing the number by two respectively. They can be used when we have to multiply or divide a number by two.  87

88. Signed Right shift operator (>>)  Shifts the bits of the number to the right and fills 0 on left as a result. The leftmost bit depends on the sign of initial number. Example 1: a = 10 a>>1 = 5 Example 2: a = -10 a>>1 = -5 We preserve the sign bit. 88

89. Left shift operator (<<) Shifts the bits of the number to the left and fills 0 on left as a result. Example : a = 5 = 0000 0101 b = -10 = 1111 0110 a << 1 = 0000 1010 = 10 a << 2 = 0001 0100 = 20 b << 1 = 0000 1010 = - 20 b << 2 = 0001 0100 = - 40 89

90. Unsigned Right shift operator (>>>) Shifts the bits of the number to the right and fills 0 on left as a result. The leftmost bit is set to 0 . (>>>) is unsigned-shift; it’ll insert 0. But (>>) is signed, and will extend the sign bit . Example 1: a = 10 a>>>1 = 5 Example 2: a = -10 a>>>1 = 2147483643 DOES NOT preserve the sign bit. 90

91. 91 Operator Meaning += Increments then assigns -= Decrements then assigns *= Multiplies then assigns /= Divides then assigns %= Modulus then assigns <<= Binary Left Shift  and assigns >>= Binary Right Shift and assigns >>>= Shift right zero fill and assigns &= Binary AND assigns ^= Binary exclusive OR and assigns |= Binary inclusive OR and assigns

92. Java instanceof Operator: The Java instanceof Operator is used to determining whether this object belongs to this particular (class or subclass or interface) or not . Syntax: object-reference instanceof type; Example: if (c instanceof Employee) Note: Employee is class & c is an instance of that class 92

93. Java Conditional Operator  (ternary): The Java Conditional Operator selects one of two expressions for evaluation, which is based on the value of the first operands. It is also called ternary operator because it takes  three arguments . Syntax : expression1 ? expression2:expression3; Example : c= a> b ? a : b ; 93

94. Control statements in java Sequential statements Control Statements ( Decision Making & loops) 94

95. Sequential statements Def : These statements are executed by JVM one by one in a sequential manner. 95

96. Control Statements Def : Which alter the flow of execution and provide better control to the programmer on the flow of execution. 96

97. Control Statements - types if if….else switch 97 while loop do….while loop for loop for-each loop break continue

98. SIMPLE IF & IF…ELSE & if….else…if (Decision making) Syntax: if(condition) { ……. } 98 Syntax: if(condition) { ……. } else { ……….. } Syntax: if(condition) { ……. } else if(condition) { ……….. } else { ….. }

99. Switch…case: Syntax: switch (expression) { case value1: statement1 ; break ; case value2: statement2 ; break ; . . case valueN : statementN ; break ; default : statementDefault ; } 99

100. Loops: while & do…while while loop: (Entry Controlled loop) Syntax : while (boolean condition) { loop statements... } 100 do….while loop: (Exit Controlled loop) Syntax : do { statements.. } while (condition);

101. Loops: for Syntax: for (initialization condition; testing condition; increment/decrement) { statement(s) } 101

102. Loops: for…each Syntax: for ( data_type variable: Collection/array ) { statement(s) } 102 Example: int arr []={10,20,30,40,50}; for( int i:arr) { System.out.println ( i ); }

103. INPUT AND OUTPUT Two Methods: InputStreamReader class & BufferedReader class Scanner class 103

104. 1) InputStreamReader class & BufferedReader class 104

105. 1) InputStreamReader class & BufferedReader class 105

106. 1) InputStreamReader class & BufferedReader class : methods 1) read () - java.io.BufferedReader.read ()  method reads a single character from this buffered reader . 2) readLine () -   java.io.BufferedReader.readline ()  method read a line of text. A line is considered to be terminated by any one of a line feed ('\n ') 106

107. 2) Scanner class Scanner is a class in java.util package U sed for obtaining the input of the primitive types like int, double, etc. and strings.  107

108. 2) Scanner class 108

109. 2) Scanner class : Methods next () - It is used to get the next complete token from the scanner which is in use. nextInt () - It scans the next token of the input as an Int. nextShort () - It scans the next token of the input as a short. nextLong () - It scans the next token of the input as a long. nextFloat () - It scans the next token of the input as a float. nextDouble () - It scans the next token of the input as a double. 109

110. Command line arguments: (I/O) java command-line argument is an argument, that is passed at the time of running the java program . The arguments passed from the console can be received in the java program via main(String args [ ]) method and it can be used as an input . 110

111. Example of command-line arguments i mport java.lang.*; class Carg { public static void main(String args []) { for(int i =0;i< args.length;i ++) System.out.println ( args [ i ]); } } 111 Compile   by D:\>   javac   Carg.java    Run   by D:\>  java  Carg   ECE sri 3 2 Output : ECE - args [0] sri - args [1] 3 - args [2] 2    - args [3]

112. Type conversion in Java Issue: When you assign value of one data type to another, the two types might not be compatible with each other.  Solution: 1) Widening or Automatic Type Conversion (Lower order to Higher order) If the data types are compatible, then Java will perform the conversion automatically known as Automatic Type Conversion. 2) Narrowing or Explicit Conversion (Higher order to lower order) If the data types are NOT compatible, they need to be casted or converted explicitly. 112

113. Type conversion in Java 1) Widening or Automatic Type Conversion (Lower order to Higher order) This happens when : The two data types are compatible. When we assign value of a smaller data type to a bigger data type . B ut no automatic conversion is supported from numeric type to char or boolean. Also , char and boolean are not compatible with each other. 113

114. Automatic Type Conversion : EXAMPLE class Test { public static void main(String[] args ) { int i = 100; // automatic type conversion long l = i ; // automatic type conversion float f = l; System.out.println ("Int value "+ i ); System.out.println ("Long value "+l); System.out.println ("Float value "+f); } } 114 OUTPUT: Int value 100 Long value 100 Float value 100.0

115. Type conversion in Java 2) Narrowing or Explicit Conversion (Higher order to lower order) If we want to assign a value of larger data type to a smaller data type we perform explicit type casting or narrowing. This is useful for incompatible data types where automatic conversion cannot be done. 115

116. Type conversion in Java Example : char and number are not compatible with each other. (Do explicit conversion) 116

117. Java arrays: Types: 1) Single Dimensional (1-D) 2) Multi Dimensional (2-D, 3-D, ….) 117

118. Java Arrays: 1-Dimensional DEF : Normally , an array is a collection of similar type of elements (Homogeneous) Java array  is an object which contains elements of a similar data type. Additionally , The elements of an array are stored in a contiguous memory location . It is a data structure where we store similar elements. We can store only a fixed set of elements in a Java array. Array in Java is index-based, the first element of the array is stored at the 0th index, 2nd element is stored on 1st index and so on. 118

119. Java Arrays: Advantages: Code Optimization:  It makes the code optimized, we can retrieve or sort the data efficiently. Random access:  We can get any data located at an index position. Disadvantages: Size Limit:  We can store only the fixed size of elements in the array. It doesn't grow its size at runtime. To solve this problem, collection framework is used in Java which grows automatically. 119

120. Array Variables: 3 step process 1)   Array Declaration 2)   Array Construction 3 )   Array Initialization/Assignment 120

121. 1)  Array Declaration Syntax: dataType [ ] array_variable ; ( or) dataType array_variable [ ]; 121 Example: i nt[ ] A; (or) int A[ ];

122. 2)   Array Construction Syntax: array_variable = new dataType [size]; Example-1: A= new int [10]; Example-2: Declaration and Construction combined: int A [ ] = new int[10]; 122

123. 3) Array Initialization / Assignment Syntax: // Assigns an integer value 1 to the first element 0 of the array A[0]= 1; // Assigns an integer value 2 to the second element 1 of the array A[1 ]=2; 123

124. 3) Array Initialization / Assignment Declaring and initialize an Array // Initilializes an integer array of length 4 where the first element is 1 , second element is 2 and so on. int A[ ] = {1, 2, 3, 4 }; 124

125. Java Array Index  Example : int[ ] age = new int[5 ]; 125

126. Java Arrays: 2-Dimensional ( Multi dimensional) Multidimensional arrays are  array of arrays   Each element of the array holding the reference of other array.  126

127. Java Arrays: 2-Dimensional (Multi dimensional) Syntax: dataType [ ][ ] array_variable ; ( or) dataType array_variable [ ][ ]; 127 Example: Int[ ][ ] A; (or) int A[ ][ ];

128. Java Arrays: 2-Dimensional (Multi dimensional) 128 //2D array or matrix - Declaration int A[ ][ ] = new int[10][20]; //2D array Initialization int A [ ][ ] = { { 2,7,9 } , { 3,6,1 } , { 7,4,2} } ;

129. Java Arrays: 2-Dimensional 129 int [ ][ ] A = new int[3][4];

130. example to initialize a 2d array ( JAGGED ARRAY ) (Different size -rows) int [ ][ ] A = { { 1, 2, 3}, { 4, 5, 6, 9}, { 7}, }; 130

131. 2d array: references 131 int Marks[ ][ ]=new int[4][3];

132. Java Arrays: 3 -Dimensional (Multi dimensional) Syntax: dataType [ ][ ][ ] array_variable ; ( or) dataType array_variable [ ][ ][ ]; 132 Example: i nt[ ][ ][ ] A; (or) int A[ ][ ][ ];

133. Java Arrays: 3-Dimensional (Multi dimensional) 133 //3D array or matrix - Declaration int A[ ][ ][ ] = new int[3][10][10 ]; //3D array Initialization int A [ ][ ][ ] = { { 2,7,9 } , { 3,6,1 } , { 7,4,2} } ;

134. Java Arrays: 3-Dimensional (Multi dimensional) //3D Array Declaration i nt A[ ][ ][ ]= new A[3][ 4][2 ]; 134

135. Java Arrays: 3-Dimensional (Multi dimensional ) Initializaion 135 int A[ ][ ][ ] = { { {1, 2, 3} , {4, 5, 6} } , { {7,8,9}, {10,11,12} } } ;

136. Access specifiers/modifiers: An access specifier is a keyword that indicates how a field/variable or method can be accessed. (i.e., scope/visibility) 136

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138. Access specifiers: 138

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140. Access specifiers: 140

141. Classes and Objects in Java Classes and Objects are basic concepts of Object Oriented Programming which revolve around the real life entities . A  class  is a group of objects which have common properties. It is a template or blueprint from which objects are created. It is a logical entity. It can't be physical. 141

142. Classes: A class is a user defined blueprint or prototype from which objects are created.   It represents the set of properties or methods that are common to all objects of one type . In general, class declarations can include these components, in order : Modifiers  : A class can be public or has default access Class name:  The name should begin with a initial letter (capitalized by convention). Superclass(if any):  The name of the class’s parent (superclass), if any, preceded by the keyword extends. A class can only extend (subclass) one parent. Interfaces(if any):  A comma-separated list of interfaces implemented by the class, if any, preceded by the keyword implements. A class can implement more than one interface. Body:  The class body surrounded by braces, { }. 142

143. Class: A class in Java can contain: Fields Methods Constructors Blocks Nested class and interface 143

144. Class: Constructors are used for initializing new objects. Fields are variables that provides the state of the class and its objects, and methods are used to implement the behavior of the class and its objects . 144

145. Object: Definitions : An object is  a real-world entity . An object is  a runtime entity . The object is  an entity which has state and behaviour . The object is  an instance of a class . 145

146. Object: 146 It is a basic unit of Object Oriented Programming and represents the real life entities.   A typical Java program creates many objects, which as you know, interact by invoking methods. characteristics of an object: State:  represents the data (value) of an object. Behavior :  represents the behavior (functionality) of an object such as deposit, withdraw, etc. Identity:  An object identity is typically implemented via a unique ID. The value of the ID is not visible to the external user. However, it is used internally by the JVM to identify each object uniquely .

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149. Class & object: Syntax to declare a class: class   class_name {         Access specifier field(s) (or) Instance Variables;    constructor;      Access specifier method(s);    }   149

150. Class & object: Instance variable in Java: A variable which is created inside the class but outside the method is known as an instance variable. Instance variable doesn't get memory at compile time . It gets memory at runtime when an object or instance is created. That is why it is known as an instance variable. 150

151. Class & object : Method in Java: In Java, a method is like a function which is used to expose the behavior of an object. Advantage of Method Code Reusability Code Optimization 151

152. Class & object : syntax class Student { private int rno ; private String name; private float cgpa ; public void input() { ----- } public void display() { ------ } } 152 //object(s) creation - Instance of class Student s1= new Student(); Student s2= new Student(); Student s3= new Student();

153. How to initialize object: 3 ways Initializing an object means storing data into the object. By reference variable By method By constructor 153

154. 1)By reference variable Syntax: object . Instance_variable = value; Example: s1.id=101 ;   s1.name=“ sri ”;    NOTE : Example TestStudent3.java 154

155. 2)By method We are creating the two objects of Student class and initializing the value to these objects by invoking the insert method .  NOTE : Example TestStudent5.java 155

156. 3)By constructor : Constructors in Java DEF: A constructor is a block of code similar to the method. It is called when an instance of the class is created. At the time of calling constructor, memory for the object is allocated in the memory . It is a special type of method which is used to initialize the object . Every time an object is created using the new() keyword, at least one constructor is called . It calls a default constructor if there is no constructor available in the class. In such case, Java compiler provides a default constructor by default. 156

157. Rules for creating Java constructor: Constructor name must be the same as its class name A Constructor must have no return type ( not even void ) A Java constructor cannot be abstract , static , final , and synchronized NOTE: We can use access modifiers while declaring a constructor.It controls the object creation. In other words, we can have private, protected, public or default constructor in Java. 157

158. TYPES OF CONSTRUCTORS: There are two types of constructors in Java: Default constructor ( no-arguments constructor) Parameterized constructor 158

159. a) Default constructor (no-arguments constructor) A constructor is called "Default Constructor" when it doesn't have any parameter . Syntax of default constructor: class_name() { …. }    Example : College.java Note : The default constructor is used to provide the default values to the object like 0, null, etc., depending on the type. 159

160. b) Parameterized constructor A constructor which has a specific number of parameters is called a parameterized constructor . Why use the parameterized constructor? The parameterized constructor is used to provide different values to distinct objects. However, you can provide the same values also . Example: Student4.java Estudent.java 160

161. Constructor Overloading in Java Constructor overloading is a technique of having more than one constructor with different parameter lists. They are arranged in a way that each constructor performs a different task. They are differentiated by the compiler by the number of parameters in the list and their types. 161

162. constructor vs method in Java Java Constructor Java Method A constructor is used to initialize the state of an object. A method is used to expose the behavior of an object. A constructor must not have a return type. A method must have a return type. The constructor is invoked implicitly. The method is invoked explicitly. The Java compiler provides a default constructor if you don't have any constructor in a class. The method is not provided by the compiler in any case. The constructor name must be same as the class name. The method name may or may not be same as the class name. 162

163. Copy of object  object : ( Java Copy Constructor) There is no copy constructor in Java. However , we can copy the values from one object to another like copy constructor in C++. There are many ways to copy the values of one object into another in Java. By constructor By assigning the values of one object into another By clone() method of Object class 163

164. 1)By constructor: copy  constructor implementation should perform deep  copy  for any referenced  objects  in the class by creating new  objects  and  copy the values It usually accepts only  one  parameter that is just  another  instance of the same class. 164

165. 3) By assigning the values of one object into another: We can copy the contents of one object into another object by assigning the values of one object into another individually field by field. 165

166. 3) By clone() method of Object class The  object cloning  is a way to create exact copy of an object. The clone() method of Object class is used to clone an object . The  clone() method  saves the extra processing task for creating the exact copy of an object. If we perform it by using the new keyword, it will take a lot of processing time to be performed that is why we use object cloning. 166

167. -----Some Programs----- 167

168. WRAPPER CLASSES: A  Wrapper class  is a  class  whose object wraps or contains a primitive data types. The   wrapper class in Java  provides the mechanism  to convert primitive into object and object into primitive . 168

169. Use of Wrapper classes in Java Java is an object-oriented programming language, so we need to deal with objects many times like in Collections , Serialization , Synchronization , etc. Change the value in Method:  Java supports only call by value. So, if we pass a primitive value, it will not change the original value. But, if we convert the primitive value in an object, it will change the original value. Serialization:  We need to convert the objects into streams to perform the serialization. If we have a primitive value, we can convert it in objects through the wrapper classes. Synchronization:  Java synchronization works with objects in Multithreading. java.util package:  The java.util package provides the utility classes to deal with objects. Collection Framework:  Java collection framework works with objects only. All classes of the collection framework ( ArrayList , LinkedList , Vector, HashSet , LinkedHashSet , TreeSet , PriorityQueue , ArrayDeque , etc.) deal with objects only. 169

170. Auto boxing & unboxing: (packing) (unpacking) Primitive object 170 Auto Boxing Un Boxing

171. Auto boxing: Automatic conversion of primitive types to the object of their corresponding wrapper classes is known as autoboxing . For example – conversion of int to Integer, long to Long, double to Double etc. 171

172. unboxing: It is just the reverse process of autoboxing . Automatically converting an object of a wrapper class to its corresponding primitive type is known as unboxing. For example – conversion of Integer to int , Long to long, Double to double etc. 172

173. Primitive Data types and Corresponding Wrapper class 173 Eight classes of the  java.lang  package are known as wrapper classes in Java.

174. Primitive to Wrapper : example ( Autoboxing ) See example, WrapperExample1.java 174

175. Wrapper to Primitive : example ( Autoboxing ) See example, WrapperExample2.java 175

176. Java Wrapper classes Example See example, WrapperExample3.java 176

177. 1) Conversion of Primitive data types to objects: Integer ival = new Integer( i ); Float fval = new Float( f ); Double dval = new Double( d ); Long lval = new Long( l ); Note : Parameter is primitive value 177

178. 2) Conversion of objects to Primitive data types : int i = ival .intValue(); float f = fval .floatValue(); l ong l = lval .longValue(); double d = dval .doubleValue(); 178

179. 3) Conversion of numbers(primitive) to strings: String s1 = Integer.toString ( i ); String s2 = Float.toString ( f ); String s3 = Double.toString ( d ); String s4 = Long.toString ( l ); 179

180. 4) Conversion of string objects to numeric objects: Integer ival = Integer.valueOf ( s1 ); Float fval = Float.valueOf ( s2 ); Double dval = Double.valueOf ( s3 ); Long lval = Long.valueOf ( s4 ); 180

181. 5) Conversion of numeric strings(objects) to primitive types(numbers): int i = Integer.parseInt ( s1 ); long l = Long.parseLong (s2); float f = Float.parseFloat ( s3 ); double d = Double.parseDouble ( s4 ); 181

182. Java String class Java String class implements three  interfaces , namely – Serializable , Comparable and CharSequence . 182

183. Strings: Def : String is a class, it is used often in the form of data type ( java.lang package ) Note : In java all classes are considered as data type(user-defined). So, we consider this String as data type. (It is not character array- but object) Example: String s1=“ Hello ”; 183

184. Create a string: There are 3 ways to create strings in java: 1) Assign a group of characters (i.e., String literal) to variable Example-1: String s1; s1=“ hello”; Example-2: String s1=“hello”; 2) Using ‘ new ’ operator (new keyword) Example: String s1=new String (“hello”); 3) By converting a character array into strings. (char array  String) Example-1: Example-2: (specified characters only) char s1[]={‘h’,’e’,’l’,’l’,’o’}; char s1 []={‘c’,’h’,’a’,’ i ’,’r’}; String s2= new String (s1); String s2= new String (s1,2,3);  air 184

185. String literal: String  s1="Welcome";   //It doesn't create a new instance    String  s2="Welcome"; Note : String objects are stored in a special memory area known as the " string constant pool ". To make Java more memory efficient (because no new objects are created if it exists already in the string constant pool). 185

186. By new keyword: //creates two objects and one reference variable   String s=new String("Welcome"); In such case, JVM will create a new string object in normal (non-pool) heap memory. 186

187. 187 Note: references are stored in stack memory and objects are stored in heap memory

188. String class methods: 1) String concatenation: Syntax : String concat(String s); Example : String s1; s1="Hello"; String s2="World"; String s3=s1.concat(s2); String s4=s1+s2; 188 Output : S3- HelloWorld S4- HelloWorld

189. String class methods: 2) String length: Syntax : int length(); Example : String s1; s1="Hello"; int n=s1.length(); 189 Output : S1- 5

190. String class methods: 3) Specific character: Syntax : char charAt ( int i ); // index-start with 0 Example : String s1; s1="Hello"; char ch =s1.charAt(1); 190 Output : S1- e

191. String class methods: 4) String comparison Syntax : int compareTo (String s1); Example : String s1=" Hello "; String s2=“hello”; int n=s1.compareTo(s2); 191 Output : String comparison: - 32 Note-1: s1==s2  0 s1<s2  - ve s1>s2  + ve Note-2: (Ignore case) int compare T o I gnore C ase (String)

192. String class methods: 5) String comparison - true/false Syntax : boolean equals(String s1); Example : String s1=" Hello "; String s2=“hello”; boolean b=s1.equals(s2); 192 Output : String comparison: false Note: Boolean equalsIgnoreCase (String s)

193. String class methods: 6) String Starts with- true/false Syntax : boolean startsWith (String s1); Example : String s1=“ ramkumar "; String s2=“ram”; boolean b=s1.startsWith(s2); 193 Output : String starts with : true Note: boolean endsWith (String s1);

194. String class methods: 7) Index of substring Syntax : int indexOf (String s1); Example : String s1=“ ramkumar "; String s2=“ kumar ”; int n=s1.indexOf(s2); 194 Output : Index of substring:3 Note: If doesn’t exist  - ve

195. String class methods: 8) Last Index of substring Syntax : int lastIndexOf (String s1); Example : String s1=“This is book,is it?"; String s2=“is”; int n=s1.lastIndexOf(s2); 195 Output : Last Index of substring:13 Note: If doesn’t exist  - ve

196. String class methods: 9 ) String substring Syntax : String substring( int ); String substring( int,int ); Example : String s1=“Welcome to java"; String s2=s1.substring(2); 196 Output : Substring: lcome to java Note: String substring(2,6); ( from, to-1) Substring : lcom

197. String class methods: 10) String conversion : lower  upper Syntax : String toLowerCase (); Example : String s1=“Welcome to java"; String s2 = s1. toUpperCase (); 197 Output : Lower to Upper:WELCOME TO JAVA Note: s1 =s2.toLowerCase(); Upper to Lower:welcome to java

198. String class methods: 11) String Trim : remove spaces (begin & end) Syntax : String trim(); Example : String s1=“ hello "; String s2 = s1. trim (); 198 Output : After Trim:hello

199. String class methods: 12) String Split: (using delimiter) Syntax : String split(String); //parameter is delimiter Example : String s1=“Hello, this is java program"; String sarr []=s1.split(" "); for(String i:sarr) System.out.println ( i ); 199 Output : Hello, this is java program

200. String class methods: 13) String - character(occurrence) Replace Syntax : String replace(char, char) Example : String s1=“Hello"; s1=s1.replace(‘ e’,’a ’); 200 Output : After replaceing:Hallo

201. Java String compare We can compare string in java on the basis of content and reference. There are three ways to compare string in java : By equals() method By = = operator By compareTo() method 201

202. 1) By equals() method The method is : equals () method & equalsIgnoreCase() It is used in  authentication. (To Check content equality) Syntax: public boolean equals(String); public boolean equalsIgnoreCase (String); 202

203. 2) By = = operator Uses == operator Used for Reference matching (i.e., whether both belong to same class type or not) Used for objects. 203

204.  String s1 = new String("HELLO");         String s2 = new String("HELLO");             System.out.println (s1 == s2); // false   204

205. 3) By compareTo() method compareTo() method Used while sorting (i.e., equality checking) Checks the order of occurrence - as per dictionary order) Syntax : int compareTo (String s1); 205 Output : String comparison: - 32 Note-1: s1==s2  0 s1<s2  - ve s1>s2  + ve Note-2: (Ignore case) int compare T o I gnore C ase (String)

206. Immutability of Strings: Objects are divided into 1) Mutable & 2) Immutable Mutable objects are objects whose contents can be modified. Immutable  simply means unmodifiable or unchangeable. Once  string  object is created its data or state can't be changed but a new  string  object is created. String objects are immutable. 206

207. mutable vs immutable: Java String is immutable and final A new String is created whenever we do String manipulation. As String manipulations are resource consuming, Java provides two utility classes: StringBuffer and StringBuilder . Let us understand the difference between these two utility classes: StringBuffer and StringBuilder are mutable classes. 207

208. StringBuffer class Java StringBuffer class is used to create mutable (modifiable) string. The StringBuffer class in java is same as String class except it is mutable i.e. it can be changed . Java StringBuffer class is thread-safe i.e. multiple threads cannot access it simultaneously. So it is safe and will result in an order. 208

209. Constructors of StringBuffer class Constructor Description StringBuffer() creates an empty string buffer with the initial capacity of 16. StringBuffer(String str ) creates a string buffer with the specified string. StringBuffer(int capacity) creates an empty string buffer with the specified capacity as length. 209

210. methods of StringBuffer class: Refer DOCUMENT….. 210

211. StringBuilder class Java StringBuilder class is used to create mutable (modifiable) string. The Java StringBuilder class is same as StringBuffer class except that it is non-synchronized. It is available since JDK 1.5. 211

212. Constructors of StringBuilder class Constructor Description StringBuilder () creates an empty string Builder with the initial capacity of 16. StringBuilder (String str ) creates a string Builder with the specified string. StringBuilder(int length) creates an empty string Builder with the specified capacity as length. 212

213. String StringBuffer StringBuilder: Immutable Strings  are read only. String  once assigned can not be changed. Mutable Mutable Storage area is SCP (String Constant Pool) Heap Memoy Heap Memory A new String is created whenever we do String manipulation. On the same string object On the same string object Consumes more memory, when we concatenate Consumes less memory, when we concatenate Consumes less memory, when we concatenate thread-safe thread-safe not thread-safe. Synchronized. String  can not be used by two  threads  simultaneously.  Synchronized. It means two threads can't call the methods simultaneously. Non- synchronized.  It means two threads can call the methods of StringBuilder simultaneously. Can safely shared between multiple threads. To be used when multiple threads are working on same String in the single threaded environment More efficient when we don’t alter the value , frequent usage is there. Less efficient than StringBuilder More efficient than StringBuffer Somewhat slower StringBuffer is faster than String  when performing simple concatenations. StringBuilder  is more  faster than  StringBuffer. 213

214. STRING CONCATENATION OPERATOR ( + ): NOTE: The  "+"  operator is overloaded for String and used to concatenated two string. Internally "+" operation is implemented using either  StringBuffer   or   StringBuilder . 214

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