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Inheritance

Inheritance. // A simple class hierarchy. // A class for two-dimensional objects. class TwoDShape { double width; double height; void showDim() { System.out.println("Width and height are " + width + " and " + height); } }. Inheritance.

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Inheritance

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  1. Inheritance // A simple class hierarchy. // A class for two-dimensional objects. class TwoDShape { double width; double height; void showDim() { System.out.println("Width and height are " + width + " and " + height); } }

  2. Inheritance // A subclass of TwoDShape for triangles. class Triangle extends TwoDShape { String style; double area() { return width * height / 2; } void showStyle() { System.out.println("Triangle is " + style); } }

  3. Inheritance class Shapes { public static void main(String args[]) { Triangle t1 = new Triangle(); Triangle t2 = new Triangle(); t1.width = 4.0; t1.height = 4.0; t1.style = "isosceles"; t2.width = 8.0; t2.height = 12.0; t2.style = "right"; System.out.println("Info for t1: "); t1.showStyle(); t1.showDim(); System.out.println("Area is " + t1.area()); System.out.println(); System.out.println("Info for t2: "); t2.showStyle(); t2.showDim(); System.out.println("Area is " + t2.area()); } }

  4. Inheritance // A subclass of TwoDShape for rectangles. class Rectangle extends TwoDShape { boolean isSquare() { if(width == height) return true; return false; } double area() { return width * height; } }

  5. Inheritance // Private members are not inherited. // This example will not compile. // A class for two-dimensional objects. class TwoDShape { private double width; // these are private double height; // now private void showDim() { System.out.println("Width and height are " + width + " and " + height); } } // A subclass of TwoDShape for triangles. class Triangle extends TwoDShape { String style; double area() { return width * height / 2; // Error! can't access } void showStyle() { System.out.println("Triangle is " + style); } }

  6. Inheritance // Use accessor methods to set and get private members. // A class for two-dimensional objects. class TwoDShape { private double width; // these are private double height; // now private // Accessor methods for width and height. double getWidth() { return width; } double getHeight() { return height; } void setWidth(double w) { width = w; } void setHeight(double h) { height = h; } void showDim() { System.out.println("Width and height are " + width + " and " + height); } }

  7. Inheritance // A subclass of TwoDShape for triangles. class Triangle extends TwoDShape { String style; double area() { return getWidth() * getHeight() / 2; } void showStyle() { System.out.println("Triangle is " + style); } }

  8. Inheritance class Shapes2 { public static void main(String args[]) { Triangle t1 = new Triangle(); Triangle t2 = new Triangle(); t1.setWidth(4.0); t1.setHeight(4.0); t1.style = "isosceles"; t2.setWidth(8.0); t2.setHeight(12.0); t2.style = "right"; System.out.println("Info for t1: "); t1.showStyle(); t1.showDim(); System.out.println("Area is " + t1.area()); System.out.println(); System.out.println("Info for t2: "); t2.showStyle(); t2.showDim(); System.out.println("Area is " + t2.area()); } }

  9. Inheritance // Add a constructor to Triangle. // A class for two-dimensional objects. class TwoDShape { private double width; // these are private double height; // now private // Accessor methods for width and height. double getWidth() { return width; } double getHeight() { return height; } void setWidth(double w) { width = w; } void setHeight(double h) { height = h; } void showDim() { System.out.println("Width and height are " + width + " and " + height); } }

  10. Inheritance // A subclass of TwoDShape for triangles. class Triangle extends TwoDShape { private String style; // Constructor Triangle(String s, double w, double h) { setWidth(w); setHeight(h); style = s; } double area() { return getWidth() * getHeight() / 2; } void showStyle() { System.out.println("Triangle is " + style); } }

  11. Inheritance class Shapes3 { public static void main(String args[]) { Triangle t1 = new Triangle("isosceles", 4.0, 4.0); Triangle t2 = new Triangle("right", 8.0, 12.0); System.out.println("Info for t1: "); t1.showStyle(); t1.showDim(); System.out.println("Area is " + t1.area()); System.out.println(); System.out.println("Info for t2: "); t2.showStyle(); t2.showDim(); System.out.println("Area is " + t2.area()); } }

  12. Inheritance // Add constructors to TwoDShape. class TwoDShape { private double width; private double height; // Parameterized constructor. TwoDShape(double w, double h) { width = w; height = h; }

  13. Inheritance // Accessor methods for width and height. double getWidth() { return width; } double getHeight() { return height; } void setWidth(double w) { width = w; } void setHeight(double h) { height = h; } void showDim() { System.out.println("Width and height are " + width + " and " + height); } }

  14. Inheritance // A subclass of TwoDShape for triangles. class Triangle extends TwoDShape { private String style; Triangle(String s, double w, double h) { super(w, h); // call superclass constructor style = s; } double area() { return getWidth() * getHeight() / 2; } void showStyle() { System.out.println("Triangle is " + style); } }

  15. Inheritance class Shapes4 { public static void main(String args[]) { Triangle t1 = new Triangle("isosceles", 4.0, 4.0); Triangle t2 = new Triangle("right", 8.0, 12.0); System.out.println("Info for t1: "); t1.showStyle(); t1.showDim(); System.out.println("Area is " + t1.area()); System.out.println(); System.out.println("Info for t2: "); t2.showStyle(); t2.showDim(); System.out.println("Area is " + t2.area()); } }

  16. exception // Use a custom exception. // Create an exception. class NonIntResultException extends Exception { int n; int d; NonIntResultException(int i, int j) { n = i; d = j; } public String toString() { return "Result of " + n + " / " + d + " is non-integer."; } }

  17. exception class CustomExceptDemo { public static void main(String args[]) { // Here, numer contains some odd values. int numer[] = { 4, 8, 15, 32, 64, 127, 256, 512 }; int denom[] = { 2, 0, 4, 4, 0, 8 }; for(int i=0; i<numer.length; i++) { try { if((numer[i]%2) != 0) throw new NonIntResultException(numer[i], denom[i]); System.out.println(numer[i] + " / " + denom[i] + " is " + numer[i]/denom[i]); }

  18. exception catch (ArithmeticException exc) { // catch the exception System.out.println("Can't divide by Zero!"); } catch (ArrayIndexOutOfBoundsException exc) { // catch the exception System.out.println("No matching element found."); } catch (NonIntResultException exc) { System.out.println(exc); } } } } 4 / 2 is 2 Can't divide by Zero! Result of 15 / 4 is non-integer. 32 / 4 is 8 Can't divide by Zero! Result of 127 / 8 is non-integer. No matching element found. No matching element found.

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