Java Novice Note 19 abstract class

1.Shap

Package Com.yfs.javase;public class Shape/*extends object */{  //default Inherit Object  object method all inherit//Calculate Area method public double Getarea () {//code completely useless System.out.println ("Calculate area"); return 0;}}

2.Circle

Package Com.yfs.javase;public Class Circle extends Shape {private double r;public Circle (double r) {THIS.R = R; SYSTEM.OUT.PRINTLN ("Create circular area"); Public double Getarea () {//override method//system.out.println for parent class ("Calculate circular area ...");//return 3.14 * R * r;//}}

3.Triangle

Package Com.yfs.javase;public class Triangle  extends Shape {private double height;private double width;public Triangle (double height, double width) {this.height = Height;this.width = width; System.out.println ("Create Triangle area"); Public double Getarea () {System.out.println ("Calculate Triangle area ..."), return 1.0/2 * width * height;}

4.Rectangle

Package Com.yfs.javase;public class Rectangle  extends Shape {private double width;private double length;public Rectangle (double width, double length) {this.width = Width;this.length = length; SYSTEM.OUT.PRINTLN ("Create rectangular area"); Public double Getarea () {System.out.println ("Calculate Rectangle area ..."); return width * length;}}

5.shap Test

Package Com.yfs.javase;public class Shapetest {public static void main (string[] args) {shape[] shapes = new Shape[10];
   shape s = new Shape ();//Create this Class object S.getarea ();}}

6. Abstract class

The abstract method class in the package com.yfs.javase;//class must be abstract public abstract class Demo1 {public abstract void method ();//No method body abstract method public A Bstract double method1 (int A, String name);    public abstract double method1 (String name,int a); An abstract class can declare that a normal method subclass can inherit public void Method2 () {System.out.println ("Call METHOD2 () ... ");} Whether the normal method can invoke the abstract method public void Method3 () {method ();//methods that do not call the parent class method to call the subclass object are polymorphic}}abstract class Child extends Demo1 {@Overridepu Blic void Method () {System.out.println ("call () ...");} Class Son extends Child {@Overridepublic double method1 (int A, String name) {//TODO auto-generated method Stubreturn 0;} @Overridepublic Double method1 (String name, int a) {//TODO auto-generated method Stubreturn 0;}} Class Children extends Demo1 {//Subclass inheriting abstract class must override abstract method @overridepublic void Method () {System.out.println ("Subclass overridden Abstract method ...");} @Overridepublic double method1 (int A, String name) {System.out.println ("name =" + name); System.out.println ("a =" + a); return 0;} @Overridepublic Double method1 (String name,int a) {//TODO auto-generated method Stubreturn 0;} public static DEMO1 test (Demo1 D) {return new Children ();}}

7. Abstract class Testing

Package Com.yfs.javase;public class Demo1test {/** * 1. Abstract classes cannot be instantiated * 2. Subclasses must override abstract methods of abstract classes */public static void Main (string[] args {Demo1 d1;//declares reference//creation Object//D1 = new Demo1 ();//abstract class cannot instantiate D1 = new Children ();d 1.method ();d 1.method2 (); Children C1 = new Children (); C1.method2 (); System.out.println ("============================");d 1.method3 () c1.method3 ();d 1.method1 (15, "Shadow Clone");D emo1 d2 = Children.test (C1);D Emo1 c2 = children.test (d1);d 2.method2 (); C2.method2 ();}}

Java Novice Note 19 abstract class