第九章(对象和类程序清单)

程序清单9-1 TestSimpleCircle.java

/*
 * 需求：定义Circle类，并使用该类创建对象。三个圆对象，其半径分别为1、25和125，然后显示着三个圆的半径和面积。
 * 然后将第二个对象的半径改为100，并显示它的新半径和面积。
 */
package com.echo.test9;

public class TestSimpleCircle {

	public static void main(String[] args) {
		// 创建半径为1的圆的对象
		SimpleCircle circle1 = new SimpleCircle();
		System.out.println("半径为" + circle1.radius + "的圆的面积是" + circle1.getArea());
		// 创建半径为25的圆的对象
		SimpleCircle circle2 = new SimpleCircle(25);
		System.out.println("半径为" + circle2.radius + "的圆的面积是" + circle2.getArea());
		// 创建半径为125的圆的对象
		SimpleCircle circle3 = new SimpleCircle(125);
		System.out.println("半径为" + circle3.radius + "的圆的面积是" + circle3.getArea());
		//将第二个对象circle2的半径改为100
		circle2.radius=100;
		System.out.println("半径为" + circle2.radius + "的圆的面积是" + circle2.getArea());

	}

}

class SimpleCircle {
	double radius;

	SimpleCircle() {
		radius = 1;
	}

	SimpleCircle(double newRadius) {
		radius = newRadius;
	}

	// 返回圆的面积
	double getArea() {
		return radius * radius * Math.PI;
	}

	// 返回圆的周长
	double getPerimeter() {
		return 2 * radius * Math.PI;
	}

	// 设置圆的半径
	void setRadius(double newRadius) {
		radius = newRadius;
	}
}

程序清单9-2 SimpleCircle.java

/*
 * 需求：定义Circle类，并使用该类创建对象。三个圆对象，其半径分别为1、25和125，然后显示着三个圆的半径和面积。
 * 然后将第二个对象的半径改为100，并显示它的新半径和面积。
 */
package com.echo.test9;

public class SimpleCircle {

	public static void main(String[] args) {
		// 创建半径为1的圆的对象
		SimpleCircle circle1 = new SimpleCircle();
		System.out.println("半径为" + circle1.radius + "的圆的面积是" + circle1.getArea());
		// 创建半径为25的圆的对象
		SimpleCircle circle2 = new SimpleCircle(25);
		System.out.println("半径为" + circle2.radius + "的圆的面积是" + circle2.getArea());
		// 创建半径为125的圆的对象
		SimpleCircle circle3 = new SimpleCircle(125);
		System.out.println("半径为" + circle3.radius + "的圆的面积是" + circle3.getArea());
		// 将第二个对象circle2的半径改为100
		circle2.radius = 100;
		System.out.println("半径为" + circle2.radius + "的圆的面积是" + circle2.getArea());
	}

	double radius;

	SimpleCircle() {
		radius = 1;
	}

	SimpleCircle(double newRadius) {
		radius = newRadius;
	}

	// 返回圆的面积
	double getArea() {
		return radius * radius * Math.PI;
	}

	// 返回圆的周长
	double getPerimeter() {
		return 2 * radius * Math.PI;
	}

	// 设置圆的半径
	void setRadius(double newRadius) {
		radius = newRadius;
	}

}

程序清单9-3 TV.java

package com.echo.test9;

public class TV {
	int channel = 1;
	int volumeLevel = 1;
	boolean on = false;

	public TV() {

	}

	public void turnOn() {
		on = true;
	}

	public void turnOff() {
		on = false;
	}

	public void setChannel(int newChannel) {
		if (on && newChannel >= 1 && newChannel <= 120) {
			channel = newChannel;
		}
	}

	public void setVolume(int newVolumeLevel) {
		if (on && newVolumeLevel >= 1 && newVolumeLevel <= 7) {
			volumeLevel = newVolumeLevel;
		}
	}

	public void channelUp() {
		if (on && channel <= 120) {
			channel++;
		}
	}

	public void channelDown() {
		if (on && channel >= 1) {
			channel--;
		}
	}

	public void volumeUp() {
		if (on && volumeLevel <= 7) {
			volumeLevel++;
		}
	}

	public void volumeDown() {
		if (on && volumeLevel >= 1) {
			volumeLevel--;
		}
	}

}

程序清单9-4 TestTV.java

package com.echo.test9;

public class TestTV {

	public static void main(String[] args) {
		TV tv1 = new TV();
		tv1.turnOn();
		tv1.setChannel(30);
		tv1.setVolume(3);

		TV tv2 = new TV();
		tv2.turnOn();
		tv2.channelUp();
		tv2.channelUp();
		tv2.volumeUp();

		System.out.println("tv1的频道是" + tv1.channel + "tv1的音量是" + tv1.volumeLevel);
		System.out.println("tv2的频道是" + tv2.channel + "tv2的音量是" + tv2.volumeLevel);

	}

}

程序清单9-6 CircleWithStaticMembers.java

package com.echo.test9;

public class CircleWithStaticMembers {

	double radius;
	static int numberOfObjects = 0;

	CircleWithStaticMembers() {
		radius = 1.0;
		numberOfObjects++;
	}

	CircleWithStaticMembers(double newRadius) {
		radius = newRadius;
		numberOfObjects++;
	}

	static int getNumberOfObjects() {
		return numberOfObjects;
	}

	double getArea() {
		return radius * radius * Math.PI;
	}

}

程序清单9-7 TestCircleWithStaticMembers.java

package com.echo.test9;

public class TestCircleWithStaticMembers {

	public static void main(String[] args) {
		System.out.println("圆对象创建之前");
		System.out.println("圆对象的数量是：" + CircleWithStaticMembers.numberOfObjects);
		// 创建c1
		CircleWithStaticMembers c1 = new CircleWithStaticMembers();
		System.out.println("创建c1之后");
		System.out.println("c1半径是：" + c1.radius + "圆对象的数量是：" + c1.numberOfObjects);
		// 创建c2
		CircleWithStaticMembers c2 = new CircleWithStaticMembers(5);
		// 修改c1
		c1.radius = 9;
		System.out.println("创建c1和修改c1之后");
		System.out.println("c1半径是：" + c1.radius + "圆对象的数量是：" + CircleWithStaticMembers.numberOfObjects);
		System.out.println("c2半径是：" + c2.radius + "圆对象的数量是：" + CircleWithStaticMembers.numberOfObjects);
	}

}