Java Unit-1.1 chunri kyu shuru kar rh koi si je di of du th n high ch ka dh hug f

Java

1. In this lecture, we will discuss: Introduction to Java. Difference between C++ and Java. 1 Lecture Objectives

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6. The Java compiler breaks the line of code into text (words) is called  Java tokens . These are the smallest element of the Java Program . The Java compiler identified these words as tokens. Types of Tokens Keywords Identifiers Literals Operators Separators Comments JAVA TOKENS

7. JAVA KEYWORDS Java has a set of keywords that are reserved words that cannot be used as variables, methods, classes, or any other identifiers. Example break, abstract, byte, boolean , etc … true, false, and null are not keywords, but they are literals and reserved words that cannot be used as identifiers. Which statement is true? Select the one correct answer. (a) new and delete are keywords in the Java language. (b) try, catch, and thrown are keywords in the Java language. (c) static, unsigned, and long are keywords in the Java language. (d) exit, class, and while are keywords in the Java language. (e) return, static, and default are keywords in the Java language. (f) for, while, and unsigned are keywords in the Java language.

8. Identifiers are used to name a variable, constant, function, class, and array. It usually defined by the user. It uses letters, underscores, or a dollar sign as the first character. Remember that the identifier name must be different from the reserved keywords. There are some rules to declare identifiers are: The first letter of an identifier must be a letter, underscore or a dollar sign. It cannot start with digits but may contain digits. The whitespace cannot be included in the identifier. Identifiers are case sensitive. Eg.   PhoneNumber  , PRICE , radius , a , a1 , _ phonenumber  , $circumference  , jagged_array . 12radius    //invalid    Identifiers

9. In programming literal is a notation that represents a fixed value (constant) in the source code. It can be categorized as an integer literal, string literal, Boolean literal, etc. It is defined by the programmer. Once it has been defined cannot be changed. Java provides five types of literals are as follows: Integer Floating Point Character String Boolean LITERALS Literal Type 23 int 9.86 double false, true boolean 'K', '7', '-' char "javatpoint" String null any reference type

10. In programming, operators are the special symbol that tells the compiler to perform a special operation . Java provides different types of operators that can be classified according to the functionality they provide. There are eight types of operators in java, are as follows: Arithmetic Operators Assignment Operators Relational Operators Unary Operators Logical Operators Ternary Operators Bitwise Operators Shift Operators OPERATORS Operator Symbols Arithmetic + , - , / , * , % Unary ++ , - - , ! Assignment = , += , -= , *= , /= , %= , ^= Relational ==, != , < , >, <= , >= Logical && , || Ternary (Condition) ? (Statement1) : (Statement2); Bitwise & , | , ^ , ~ Shift << , >> , >>>

11. The separators in Java is also known as  punctuators . There are nine separators in Java, are as follows: Square Brackets []:  It is used to define array elements. A pair of square brackets represents the single-dimensional array, two pairs of square brackets represent the two-dimensional array. Parentheses ():  It is used to call the functions and parsing the parameters. Curly Braces {}:  The curly braces denote the starting and ending of a code block. Comma (,):  It is used to separate two values, statements, and parameters. Assignment Operator (=):  It is used to assign a variable and constant. Semicolon (;):  It is the symbol that can be found at end of the statements. It separates the two statements. Period (.):  It separates the package name form the sub-packages and class. It also separates a variable or method from a reference variable. SEPARATORS

12. Comments allow us to specify information about the program inside our Java code. Java compiler recognizes these comments as tokens but excludes it form further processing. The Java compiler treats comments as whitespaces. Java provides the following two types of comments: Line Oriented:  It begins with a pair of forwarding slashes ( // ). Block-Oriented:  It begins with /* and continues until it founds  */ . COMMENTS

13. Data types specify the different sizes and values that can be stored in the variable. There are two types of data types in Java: Primitive data types:  The primitive data types include boolean , char, byte, short, int, long, float and double. Non-primitive data types:  The non-primitive data types include  Classes, Interfaces and Arrays. There are 8 types of primitive data types: boolean data type byte data type char data type short data type int data type long data type float data type double data type DATA TYPES Data Type Default Value Default size boolean false 1 bit char '\u0000' 2 byte byte 1 byte short 2 byte int 4 byte long 0L 8 byte float 0.0f 4 byte double 0.0d 8 byte

14. The access modifiers in Java specifies the accessibility or scope of a field, method, constructor, or class. We can change the access level of fields, constructors, methods, and class by applying the access modifier on it. There are four types of Java access modifiers: Private : The access level of a private modifier is only within the class. It cannot be accessed from outside the class. Default : The access level of a default modifier is only within the package. It cannot be accessed from outside the package. If you do not specify any access level, it will be the default. Protected : The access level of a protected modifier is within the package and outside the package through child class. If you do not make the child class, it cannot be accessed from outside the package. Public : The access level of a public modifier is everywhere. It can be accessed from within the class, outside the class, within the package and outside the package. ACCESS MODIFIERS

15. Access Modifier within class within package outside package by subclass only outside package Private Y N N N Default Y Y N N Protected Y Y Y N Public Y Y Y Y

16. class  A{   private   int  data= 40 ;   private   void   msg (){ System.out.println ( "Hello java" );}   }      public   class  Simple{     public   static   void  main(String  args []){      A  obj = new  A();       System.out.println ( obj.data ); // COMPILER ERROR    obj.msg(); // COMPILE TIME ERROR    }   }   Private Example

17. //save by A.java    package  pack;   class  A{      void   msg (){ System.out.println ( "Hello" );}   }   //save by B.java    package   mypack ;   import  pack.*;   class  B{      public   static   void  main(String  args []){      A  obj  =  new  A(); //Compile Time Error       obj.msg(); //Compile Time Error      }   }   Default Example

18. //save by A.java    package  pack;   public   class  A{   protected   void   msg (){ System.out.println ( "Hello" );}   }   //save by B.java    package   mypack ;   import  pack.*;      class  B  extends  A{      public   static   void  main(String  args []){      B  obj  =  new  B();      obj.msg();     }   }   Protected Example

19. //save by A.java    package  pack;   public   class  A{   protected   void   msg (){ System.out.println ( "Hello" );}   }   //save by B.java    package   mypack ;   import  pack.*;      class  B  {      public   static   void  main(String  args []){      A  obj  =  new  A();      obj.msg();     }   }   Public Example

20. Normally, an array is a collection of similar type of elements which has contiguous memory location. 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. Arrays

21. 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. There are two types of array. Single Dimensional Array Multidimensional Array Syntax to Declare an Array in Java dataType []  arr ; (or)   dataType  [] arr ; (or)   dataType   arr [];  

22. //Java Program to illustrate how to declare, instantiate, initialize    //and traverse the Java array.    class   Testarray {   public   static   void  main(String  args []){   int  a[]= new   int [ 5 ]; //declaration and instantiation    a[ ]= 10 ; //initialization    a[ 1 ]= 20 ;   a[ 2 ]= 70 ;   a[ 3 ]= 40 ;   a[ 4 ]= 50 ;   //traversing array    for ( int   i = ;i< a.length;i ++) //length is the property of array    System.out.println (a[ i ]);   }}   Single Dimensional Array Example

23. //Java Program to print the array elements using for-each loop    class  Testarray1{   public   static   void  main(String  args []){   int   arr []={ 33 , 3 , 4 , 5 };   //printing array using for-each loop    for ( int  i:arr)   System.out.println ( i );   }}   Array using for-each loop

24. Syntax to Declare Multidimensional Array in Java dataType [][]  arrayRefVar ; (or)   dataType  [][] arrayRefVar ; (or)   dataType   arrayRefVar [][]; (or)   dataType  [] arrayRefVar [];   MULTIDIMENSIONAL ARRAY

25. //Java Program to illustrate the use of multidimensional array    class  Testarray3{   public   static   void  main(String  args []){   //declaring and initializing 2D array    int   arr [][]={{ 1 , 2 , 3 },{ 2 , 4 , 5 },{ 4 , 4 , 5 }};   //printing 2D array    for ( int   i = ;i< 3 ;i++){     for ( int  j= ;j< 3 ;j++){       System.out.print ( arr [ i ][j]+ " " );    }     System.out.println ();   }   }}   EXAMPLE

26. Jagged Array in Java If we are creating odd number of columns in a 2D array, it is known as a jagged array. In other words, it is an array of arrays with different number of columns. A jagged array is an array of arrays such that member arrays can be of different sizes, i.e., we can create a 2-D array but with a variable number of columns in each row. These types of arrays are also known as Jagged arrays. JAGGED ARRAY

27. //Java Program to illustrate the jagged array    class   TestJaggedArray {        public   static   void  main(String[]  args ){            //declaring a 2D array with odd columns             int   arr [][] =  new   int [ 3 ][];            arr [ ] =  new   int [ 3 ];            arr [ 1 ] =  new   int [ 4 ];            arr [ 2 ] =  new   int [ 2 ];            //initializing a jagged array             int  count =  ;            for  ( int   i = ;  i < arr.length ;  i ++)                for ( int  j= ; j< arr [ i ].length;  j++ )                    arr [ i ][j] = count++;                //printing the data of a jagged array              for  ( int   i = ;  i < arr.length ;  i ++){                for  ( int  j= ; j< arr [ i ].length;  j++ ){                    System.out.print ( arr [ i ][j]+ " " );               }                System.out.println (); //new line            }       }   }