java新手笔记19 抽象类

1.Shap

package com.yfs.javase;



public class Shape /*extends Object */{  //默认继承object  object方法全部继承

	//计算面积方法

	public double getArea() {//代码完全没用

		System.out.println("计算面积");

		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("创建圆形面积");

	}

	

//	public double getArea() {//覆盖父类的方法

//		System.out.println("计算圆形面积...");

//		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("创建三角形面积");

	}

	

	public double getArea() {

		System.out.println("计算三角形面积...");

		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("创建矩形面积");

	}

	

	public double getArea() {

		System.out.println("计算矩形面积...");

		return width * length;

	}



}

 5.shap测试

package com.yfs.javase;



public class ShapeTest {



	public static void main(String[] args) {

		 Shape[] shapes = new Shape[10];

		 

		 Shape s = new Shape();//创建这个类对象

		 s.getArea();



	}



}

 6.抽象类

package com.yfs.javase;

//类中有抽象方法 类必须是抽象的

public abstract class Demo1 {

	

	public abstract  void method(); //没有方法体  抽象方法

	public abstract  double method1(int a, String name); 

	public abstract  double method1(String name,int a); 

   //抽象类可以声明普通方法   子类可以继承

	public void method2() {

		System.out.println("call method2()... ");

	}

	//普通方法是否可调用抽象方法

	public void method3() {

		method();//不会调用父类的方法  调用子类对象的方法  多态

	}

}

abstract class Child extends Demo1 {

	@Override

	public void method() {

		System.out.println("call () .......");

	}

}

class Son extends Child {



	@Override

	public double method1(int a, String name) {

		// TODO Auto-generated method stub

		return 0;

	}



	@Override

	public double method1(String name, int a) {

		// TODO Auto-generated method stub

		return 0;

	}

	

}



class Children extends Demo1 {

	//子类继承抽象类   必须覆盖抽象方法

	@Override

	public void method() {

		System.out.println("子类覆盖的抽象方法...");

		

	}



	@Override

	public double method1(int a, String name) {

		System.out.println("name = " + name);

		System.out.println("a = " + a);

		return 0;

	}



	@Override

	public double method1(String name, int a) {

		// TODO Auto-generated method stub

		return 0;

	}

	

	public static Demo1 test (Demo1 d) {

		

		return new Children();

	}

	

}

 7.抽象类测试

package com.yfs.javase;



public class Demo1Test {



	/**

	 * 1.抽象类不能实例化

	 * 2.子类必须覆盖抽象类的抽象方法

	 */

	public static void main(String[] args) {

		Demo1 d1;//声明引用

		//创建对象

		//d1 = new Demo1();//抽象类不能实例化

		d1 = new Children();

		d1.method();

		d1.method2();

		

		Children c1 = new Children();

		c1.method2();

		

		System.out.println("============================");

		

		d1.method3();

		c1.method3();

		

		d1.method1(15, "影分身");

		

		Demo1 d2 = Children.test(c1);

		Demo1 c2 = Children.test(d1);

		d2.method2();

		c2.method2();

		



	}



}