STATIC VARIABLE/ METHODS, INHERITANCE, INTERFACE AND COMMAND LINE ARGUMENTS

Transcription

1 STATIC VARIABLE/ METHODS, INHERITANCE, INTERFACE AND COMMAND LINE ARGUMENTS Example 1: Static Member Variable 1. /* 2. This Java Example shows how to declare and use static member variable inside a java class. 3. */ public class StaticMemberExample 6. { 7. public static void main(string[] args) 8. { 9. ObjectCounter object1 = new ObjectCounter(); 10. System.out.println(object1.getNumberOfObjects()); ObjectCounter object2 = new ObjectCounter(); 13. System.out.println(object2.getNumberOfObjects()); 14. } 15. } class ObjectCounter 18. { 19. /* 20. * Static members are class level variables and shared by all 21. * the objects of the class. 22. * To define static member, use static keyword 23. * e.g. static int i=0; 24. * 25. * Please note that static member variables can be accessed 26. * inside non static methods because they are class level 27. * variables. 28. */ static int counter=0; public ObjectCounter() 33. { /*increase the object counter. Since only one varible 36. *is shared between all objects of this class, it 37. *always return number of objects till now. 38. */ 39. counter++; 40. } //returns number of objects created till now 43. public int getnumberofobjects() 44. { 45. return counter; 46. } 47. } Page 1

2 Example 2: Static Method 1. /* 2. This Java Example shows how to declare and use static methods inside 3. a java class. 4. */ public class StaticMethodExample 7. { public static void main(string[] args) 10. { int result = MathUtility.add(1, 2); 13. System.out.println("(1+2) is : " + result); 14. } } class MathUtility 19. { /* 22. * To declare static method use static keyword. 23. * Static methods are class level methods and can not access 24. * any instance 25. * member directly. However, it can access member's of a 26. * particular object 27. * using its reference. 28. * 29. * Static methods are generally written as a utility method or 30. * it performs task for all objects of the class. 31. * 32. */ public static int add(int first, int second) 35. { 36. return first + second; 37. } 38. } Page 2

3 Example 3: Inheritance 1. //Inheritance, In Java You Can Only Inherit from One Class, 2. //Multiple Inheritance is not allowed class Parent 5. { 6. //data members 7. private int a; 8. public int b; 9. protected int c; //default constructor 12. public Parent() 13. { 14. a = b = c = 0; 15. System.out.println("I am class A's default constructor"); 16. } //parameterized constructor 19. public Parent(int a, int b, int c) 20. { 21. this.a = a; 22. this.b = b; 23. this.c = c; 24. } //get and set methods for a 27. public int geta() 28. { 29. return a; 30. } public void seta(int a) 33. { 34. this.a = a; 35. } //get and set methods for b 38. public int getb() 39. { 40. return b; 41. } public void setb(int b) 44. { 45. this.b = b; 46. } //get and set methods for c 49. public int getc() 50. { 51. return c; 52. } Page 3

4 53. public void setc(int c) 54. { 55. this.c = c; 56. } 57. } //child class inherit the properties of Parent 60. public class Child extends Parent 61. { 62. //default constructor 63. public Child() 64. { 65. System.out.println("I am class B's default constructor"); 66. } //parameterized constructor 69. public Child(int a, int b, int c) 70. { 71. //calling base class (A's) parameterized constructor 72. super(a,b,c); 73. } public static void main(string args[]) 76. { 77. Child obj1 = new Child(); 78. Child obj2 = new Child(1,2,3); //Assigning Child's Reference To Parent 81. Parent objp = new Child(); System.out.println("\nThe value of a can-not be accessed directly in child bcz its private in parent"); 84. System.out.println("\nThe value of b = " + obj2.b); 85. System.out.println("\nThe value of c = " + obj2.c); 86. } 87. } Page 4

5 Example 4: Constructor Call Sequence in Inheritance 1. //Constructor call sequence in inheritance class GrandFather 4. { 5. //Default Constructor 6. public GrandFather() 7. { 8. System.out.println("Grand Father's Constructor"); 9. } 10. } class Father extends GrandFather 13. { 14. //Default Constructor 15. public Father() 16. { 17. System.out.println("Father's Constructor"); 18. } 19. } class Child1 extends Father 22. { 23. //Default Constructor 24. public Child1() 25. { 26. System.out.println("Child1's Constructor"); 27. } 28. } class Child2 extends Father 31. { 32. //Default Constructor 33. public Child2() 34. { 35. System.out.println("Child2's Constructor"); 36. } 37. } class CallingCons 40. { 41. //Main function 42. public static void main(string []args) 43. { 44. Child1 objc1 = new Child1(); 45. System.out.println(); 46. Child2 objc2 = new Child2(); 47. } 48. } Page 5

6 Example 5: Usage of super 1. /*usage of super, method overriding and member overriding*/ class Parent 4. { 5. int num; //Function to tell about the class 8. void TellAbout() 9. { 10. System.out.println("Hello, I am Parent called by super"); 11. } 12. } class Child extends Parent 15. { 16. //hidding num1 of Parent 17. int num; //paremetrized constructor of child 20. public Child(int num1, int num2) 21. { 22. super.num = num1; 23. num = num2; 24. } //function to display the vlaues 27. void Display() 28. { 29. System.out.println("num in Parent Class = " + super.num); 30. System.out.println("num in Child Class = " + num); 31. } //function to tell about the class, (overridden method) 34. void TellAbout() 35. { 36. super.tellabout(); 37. System.out.println("Hello, I am child"); 38. } 39. } class UsingSuper 42. { 43. public static void main(string []args) 44. { 45. Child obj = new Child(2,3); 46. obj.tellabout(); 47. obj.display(); 48. } 49. } Page 6

7 Example 6: Abstract Class 1. /*abstract classes and abstract method. 2. *You cant intansiate the object of abstract class. 3. *To access the functionality of the abstract class 4. *you have to inherit it into sub-class 5. *you can provide only declaration of methods with abstract key-word 6. *you can provide implementation of methods in it 7. *you have to provide the defination of abstract methods in sub-class 8. *otherwise the sub-class becomes abstract as well*/ 9. abstract class DrawingShapes 10. { 11. //data member 12. String ShapeType; 13. //abstract mehtod whose implementation required in sub-class 14. abstract void draw(); 15. //con-crete methods are still allowed in abstract class 16. void BackGroundColor(String color) 17. { 18. System.out.println(ShapeType + " Drawn With Back-Ground-Color " + color); 19. } 20. } 21. //Circle class, extending the DrawingShapes 22. class Circle extends DrawingShapes 23. { 24. //implementation of abstract method 25. void draw() 26. { 27. ShapeType = "Circle"; 28. } 29. } 30. //Rectangle class, extending the Drawing Shpaes 31. class Rectangle extends DrawingShapes 32. { 33. //implementation of abstract method 34. void draw() 35. { 36. ShapeType = "Rectangle"; 37. } 38. } Page 7

8 39. class UsingAbstract 40. { 41. public static void main(string []args) 42. { 43. //object of type Circle 44. Circle c = new Circle(); //object of type Rectangle 47. Rectangle r = new Rectangle(); //obtain a reference of type DrawingShapes (abstract class) 50. DrawingShapes ds; //calling draw method of Circle class 53. c.draw(); //calling BackGroundColor method of Circle class 56. c.backgroundcolor("yellow"); //ds of abstract class, refers to Rectangle class's object 59. ds = r; //calling draw mehtod of Rectangle class 62. ds.draw(); //calling BackGroundColor method of Rectangle class 65. ds.backgroundcolor("blue"); 66. } 67. } Page 8

9 Example 7: Creating and Using Interface 1. //declaring a simple interface that contains five abstract mehtods 2. interface ISimpleMath 3. { 4. float Add(float num1, float num2); 5. float Sub(float num1, float num2); 6. float Mul(float num1, float num2); 7. float Div(float num1, float num2); 8. float Rem(float num1, float num2); 9. } //implementing the ISimpleMath interface (declared above) in //Calculator class 12. class Calculator implements ISimpleMath 13. { 14. //implementation of the interface methods 15. //implementing Add(Addition) function 16. public float Add(float num1, float num2) 17. { 18. return num1 + num2; 19. } //implementing Sub(Subtraction) function 22. public float Sub(float num1, float num2) 23. { 24. return num1 - num2; 25. } //implementing Mul(multiply) function 28. public float Mul(float num1, float num2) 29. { 30. return num1 * num2; 31. } //implementing Div(Division) function 34. public float Div(float num1, float num2) 35. { 36. return num1 / num2; 37. } //implementing Rem(Remainder) function 40. public float Rem(float num1, float num2) 41. { 42. return num1 % num2; 43. } //get and set property methods for num1 46. public float GetNum1() 47. { 48. return num1; 49. } Page 9

10 54. public void SetNum1(float num1) 55. { 56. this.num1 = num1; 57. } //get and set property methods for num2 60. public float GetNum2() 61. { 62. return num2; 63. } public void SetNum2(float num2) 66. { 67. this.num2 = num2; 68. } //class function to take input, by using Keyboard class 71. void TakeInput() 72. { 73. System.out.print(" Enter First Number = "); 74. num1 = Keyboard.readFloat(); System.out.print(" Enter Second Number = "); 77. num2 = Keyboard.readFloat(); 78. } //class function to display results 81. void Display(float a, float s, float m, float d, float r) 82. { 83. System.out.println(" Sum = " + a); 84. System.out.println(" Sub = " + s); 85. System.out.println(" Mul = " + m); 86. System.out.println(" Div = " + d); 87. System.out.println(" Rem = " + r); 88. } //Main Function 91. public static void main(string args[]) 92. { 93. //Creating an object of Calculator class 94. Calculator objc = new Calculator(); //Calling input function of Calculator class 97. objc.takeinput(); //calling calculation methods of Calculator class 100. float a = objc.add(objc.getnum1(), objc.getnum2()); 101. float s = objc.sub(objc.getnum1(), objc.getnum2()); 102. float m = objc.mul(objc.getnum1(), objc.getnum2()); 103. float d = objc.div(objc.getnum1(), objc.getnum2()); 104. float r = objc.rem(objc.getnum1(), objc.getnum2()); //Displaying the result of calculation 107. objc.display(a, s, m, d, r); 108. } Page 10

11 109. //class data members 110. private float num1; 111. private float num2; 112. } Example 8: Displaying Command Line Arguments Passed to the Program 1. class CommandLineArgs 2. { 3. public static void main(string []args) 4. { 5. //getting the length of passed arguments 6. int len = args.length; 7. if(len==0) 8. { 9. System.out.println("No Argument(s) Have Been Passed"); 10. } 11. else 12. { 13. //displaying the passed arguments 14. for(int i=0; i<len; i++) 15. System.out.println("The Argument At Location args[ "+ i + " ] is " + args[i]); 16. } 17. } 18. } THE END Page 11