IntroductionJava Programming - Math Class

Java- Math Class

1. Standard Classes and Methods: The Math Class: Java Math class provides several methods to work on math calculations Fundamentals of Java 2 Table 4-1: Seven methods in the Math class

2. Standard Classes and Methods: The Math Class (cont.) Using sqrt() method example: Fundamentals of Java 3

3. Standard Classes and Methods: The Math Class (cont.) Fundamentals of Java 4 Math class methods example:

4. Standard Classes and Methods: The Random Class Random number generator: Returns numbers chosen at random from a pre-designated interval Fundamentals of Java 5 Table 4-2: Methods in the Random class

5. Java Methods 6

6. Defining Methods 7

7. Defining Methods 8 A method is a collection of statements that are grouped together to perform an operation.

8. Defining Methods 9 A method is a collection of statements that are grouped together to perform an operation.

9. Method Signature 10 Method signature is the combination of the method name and the parameter list.

10. Formal Parameters 11 The variables defined in the method header are known as formal parameters .

11. Actual Parameters 12 When a method is invoked, you pass a value to the parameter. This value is referred to as actual parameter or argument .

12. Return Value Type 13 A method may return a value. The returnValueType is the data type of the value the method returns. If the method does not return a value, the returnValueType is the keyword void . For example, the returnValueType in the main method is void .

13. Calling Methods 14

14. Reuse Methods from Other Classes NOTE: One of the benefits of methods is for reuse. The max method can be invoked from any class besides TestMax . If you create a new class Test , you can invoke the static method max using ClassName.methodName (e.g., TestMax.max ). 15

15. void Method Example 16

16. Passing Parameters 17

17. Pass by Value 18 When you invoke a method with an argument, the value of the argument is passed to the parameter. This is referred to as pass-by-value. If the argument is a variable rather than a literal value, the value of the variable is passed to the parameter. The variable is not affected, regardless of the changes made to the parameter inside the method

18. Pass by Value 19

19. Overloading Methods Overloading methods enables you to define the methods with the same name as long as their signatures are different. The max method that was used earlier works only with the int data type. But what if you need to determine which of two floating-point numbers has the maximum value? The solution is to create another method with the same name but different parameters, as shown in the following code: public static double max( double num1, double num2) { if (num1 > num2) return num1; else return num2; } 20

20. Ambiguous Invocation The Java compiler determines which method to use based on the method signature. Sometimes there may be two or more possible matches for an invocation of a method, but the compiler cannot determine the most specific match. This is referred to as ambiguous invocation . Ambiguous invocation is a compile error. 21

21. Ambiguous Invocation 22

22. Scope of Local Variables A local variable : a variable defined inside a method. Scope : the part of the program where the variable can be referenced. The scope of a local variable starts from its declaration and continues to the end of the block that contains the variable. A local variable must be declared before it can be used. 23

23. Scope of Local Variables, cont. You can declare a local variable with the same name multiple times in different non-nesting blocks in a method, but you cannot declare a local variable twice in nested blocks. 24

24. Scope of Local Variables, cont. A variable declared in the initial action part of a for loop header has its scope in the entire loop. But a variable declared inside a for loop body has its scope limited in the loop body from its declaration and to the end of the block that contains the variable. 25

25. Scope of Local Variables, cont. 26

26. Benefits of Methods 27 Write a method once and reuse it anywhere. Information hiding. Hide the implementation from the user. Reduce complexity.

27. Arrays An array is an ordered list of values 28 0 1 2 3 4 5 6 7 8 9 79 87 94 82 67 98 87 81 74 91 An array of size N is indexed from zero to N-1 scores The entire array has a single name Each value has a numeric index This array holds 10 values that are indexed from 0 to 9

28. Arrays A particular value in an array is referenced using the array name followed by the index in brackets For example, the expression scores[2] refers to the value 94 (the 3rd value in the array) That expression represents a place to store a single integer and can be used wherever an integer variable can be used 29

29. Arrays For example, an array element can be assigned a value, printed, or used in a calculation : scores[2] = 89; scores[first] = scores[first] + 2; mean = (scores[0] + scores[1])/2; System.out.println ("Top = " + scores[5]); 30

30. Arrays The values held in an array are called array elements An array stores multiple values of the same type (the element type ) The element type can be a primitive type or an object reference Therefore, we can create an array of integers, or an array of characters, or an array of String objects, etc. In Java, the array itself is an object Therefore the name of the array is a object reference variable, and the array itself must be instantiated 31

31. Declaring Arrays The scores array could be declared as follows: int[] scores = new int[10]; The type of the variable scores is int[] (an array of integers) Note that the type of the array does not specify its size, but each object of that type has a specific size The reference variable scores is set to a new array object that can hold 10 integers 32

32. Declaring Arrays Some examples of array declarations: float[] prices = new float[500]; boolean[] flags; flags = new boolean[20]; char[] codes = new char[1750]; 33

33. Bounds Checking Once an array is created, it has a fixed size An index used in an array reference must specify a valid element That is, the index value must be in bounds (0 to N-1) The Java interpreter throws an ArrayIndexOutOfBoundsException if an array index is out of bounds This is called automatic bounds checking 34

34. Bounds Checking For example, if the array codes can hold 100 values, it can be indexed using only the numbers 0 to 99 If count has the value 100, then the following reference will cause an exception to be thrown: System.out.println (codes[count]); It’s common to introduce off-by-one errors when using arrays 35 for (int index=0; index <= 100; index++) codes[index] = index*50 + epsilon; problem

35. Bounds Checking Each array object has a public constant called length that stores the size of the array It is referenced using the array name: scores.length Note that length holds the number of elements, not the largest index 36

36. Alternate Array Syntax The brackets of the array type can be associated with the element type or with the name of the array Therefore the following declarations are equivalent: float[] prices; float prices[]; The first format generally is more readable 37

37. Initializer Lists An initializer list can be used to instantiate and initialize an array in one step The values are delimited by braces and separated by commas Examples: int[] units = {147, 323, 89, 933, 540, 269, 97, 114, 298, 476}; char[] letterGrades = {'A', 'B', 'C', 'D', ’F'}; 38

38. Initializer Lists Note that when an initializer list is used: the new operator is not used no size value is specified The size of the array is determined by the number of items in the initializer list An initializer list can only be used only in the array declaration 39

39. Arrays as Parameters An entire array can be passed as a parameter to a method Like any other object, the reference to the array is passed, making the formal and actual parameters aliases of each other Changing an array element within the method changes the original An array element can be passed to a method as well, and follows the parameter passing rules of that element's type 40

40. Arrays of Objects The elements of an array can be object references The following declaration reserves space to store 53 references to String objects String[] words = new String[53]; It does NOT create the String objects themselves Each object stored in an array must be instantiated separately 41

41. Command-Line Arguments The signature of the main method indicates that it takes an array of String objects as a parameter These values come from command-line arguments that are provided when the interpreter is invoked For example, the following invocation of the interpreter passes an array of three String objects into main : > java delhi colcutta jaipur bangalore These strings are stored at indexes 0-3 of the parameter 42

42. Arrays of Objects Objects can have arrays as instance variables Many useful structures can be created with arrays and objects The software designer must determine carefully an organization of data and objects that makes sense for the situation 43

43. Two-Dimensional Arrays A one-dimensional array stores a list of elements A two-dimensional array can be thought of as a table of elements, with rows and columns 45 one dimension two dimensions

44. Two-Dimensional Arrays To be precise, a two-dimensional array in Java is an array of arrays A two-dimensional array is declared by specifying the size of each dimension separately: int[][] scores = new int[12][50]; A two-dimensional array element is referenced using two index values value = scores[3][6] The array stored in one row or column can be specified using one index 46

45. Two-Dimensional Arrays Expression Type Description scores int[][] 2D array of integers, or array of integer arrays scores[5] int[] array of integers scores[5][12] int integer 47

46. Multidimensional Arrays An array can have many dimensions If it has more than one dimension, it is called a multidimensional array Each dimension subdivides the previous one into the specified number of elements Each array dimension has its own length constant Because each dimension is an array of array references, the arrays within one dimension can be of different lengths these are sometimes called ragged arrays 48

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