Java 练习(多态性练习二)

例子一：

InstanceTest.java

package com.klvchen.exer;

public class InstanceTest {
	
	public static void main(String[] args) {
		
		InstanceTest test = new InstanceTest();
		test.method(new Graduate());
	}
	
	public void method(Person e) {
		
		String info = e.getInfo();
		System.out.println(info);
		
		if(e instanceof Graduate) {
			System.out.println("a graduated student");
		}
		
		if(e instanceof Student) {
			System.out.println("a student");
		}
		
		if(e instanceof Person) {
			System.out.println("a person");
		}
		
	}

}

class Person{
	protected String name = "person";
	protected int age = 50;
	
	public String getInfo() {
		return "Name: " + name + "
" + "age: " + age;
	}
}

class Student extends Person{
	protected String school = "pku";
	
	public String getInfo() {
		return "Name: " + name + "
age: " + age + "
school: " + school;
	}
}

class Graduate extends Student {
	public String major = "IT";
	
	public String getInfo() {
		return "Name: " + name + "
age: " + age + "
school: " + school + "
major" + major;
	}
}

运行结果:

例子二：

定义一个测试类GeometricTest,
编写equalsArea方法测试两个对象的面积是否相等（注意方法的参数类型,利用动态绑定技术)，
编写displayGeometricobject方法显示对象的面积(注意方法的参数类型，利用动态绑定技术)。

GeometricObject.java

package com.klvchen.exer1;

public class GeometricObject {
	
	protected String color;
	protected double weight;
	
	public String getColor() {
		return color;
	}
	
	public void setColor(String color) {
		this.color = color;
	}
	
	public double getWeight() {
		return weight;
	}
	
	public void setWeight(double weight) {
		this.weight = weight;
	}
	
	public GeometricObject(String color, double weight) {
		super();
		this.color = color;
		this.weight = weight;
	}
	
	public double findArea() {
		return 0.0;
	}
}

Circle.java

package com.klvchen.exer1;

public class Circle extends GeometricObject {
	
	private double radius;

	public Circle(double radius, String color, double weight) {
		super(color, weight);
		this.radius = radius;
	}

	public double getRadius() {
		return radius;
	}

	public void setRadius(double radius) {
		this.radius = radius;
	}
	
	@Override
	public double findArea() {
		return 3.14 * radius * radius;
	}
}

MyRectangle.java

package com.klvchen.exer1;

public class MyRectangle extends GeometricObject {
	
	private double width;
	private double height;
	
	public MyRectangle(double width, double height, String color, double weight) {
		super(color, weight);
		this.width = width;
		this.height = height;
	}

	public double getWidth() {
		return width;
	}

	public void setWidth(double width) {
		this.width = width;
	}

	public double getHeight() {
		return height;
	}

	public void setHeight(double height) {
		this.height = height;
	}
	
	@Override
	public double findArea() {
		return width * height;
	}
}

GeometricTest.java

package com.klvchen.exer1;

public class GeometricTest {
	
	public static void main(String[] args) {
		GeometricTest test = new GeometricTest();
		
		Circle c1 = new Circle(3.3, "white", 1.0);
		test.displayGeometricObject(c1);
		Circle c2 = new Circle(3.3, "white", 1.0);
		test.displayGeometricObject(c2);
		
		boolean isEquals = test.equalsArea(c1, c2);
		System.out.println("c1 和 c2 的面积是否相等: " + isEquals);
		
		MyRectangle rect = new MyRectangle(2.1, 3.4, "red", 2.0);
		test.displayGeometricObject(rect);
		
	}

	public void displayGeometricObject(GeometricObject o) {
		System.out.println("面积为: " + o.findArea());
	}
	
	//测试两个对象的面积是否相等
	public boolean equalsArea(GeometricObject o1, GeometricObject o2) {
		return o1.findArea() == o2.findArea();
	}
}

运行结果：