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();

	}

}