（笔记）多态：向上转型，返回值类型实现多态（工厂方法）

以下是例题：

以下类都在同一包中：

        使用Factory类，将个子类实例化并赋值给一个父类实例，并将此父类实例作为返回值，然后在Test类中用此返回值调用抽象方法。

package day0802.ch13.lx.lx01;
public class Test {
	public static void main(String[] args) {
		
		Factory factory=new Factory();
		
		factory.generate(1).print();;
		factory.generate(2).print();
		factory.generate(3).print();
	}
}

运行结果：

针式打印机--打印速度慢，效果差，噪音高
喷墨打印机--打印速度一般，效果一般，噪音一般
激光打印机--打印速度快，效果好，噪音低

package day0802.ch13.lx.lx01;
public class Factory {
	public Printer generate(int i) {
		Printer p=null;
		if(i==1) {
			p=new DotMatrixPrinter("慢","差","高");
		}else if(i==2) {
			p=new InkpetPrinter("一般","一般","一般");
		}else if(i==3) {
			p=new LaserPrinter("快","好","低");
		}
		return p;	
	}
}

package day0802.ch13.lx.lx01;

public abstract class Printer {
	private String speed;
	private String effect;
	private String noise;
	
	public abstract void print();
	
	//构造方法
	public Printer(){}
	public Printer(String speed, String effect, String noise) {
		super();
		this.speed = speed;
		this.effect = effect;
		this.noise = noise;
	}
	//get set
	public String getSpeed() {
		return speed;
	}
	public void setSpeed(String speed) {
		this.speed = speed;
	}
	public String getEffect() {
		return effect;
	}
	public void setEffect(String effect) {
		this.effect = effect;
	}
	public String getNoise() {
		return noise;
	}
	public void setNoise(String noise) {
		this.noise = noise;
	}
}

package day0802.ch13.lx.lx01;
public class DotMatrixPrinter extends Printer {
	
	@Override
	public void print() {
		System.out.println("针式打印机--打印速度"+this.getSpeed()+"，效果"+this.getEffect()+"，噪音"+this.getNoise());

	}	
	//构造方法
	public DotMatrixPrinter() {}
	public DotMatrixPrinter(String speed, String effect, String noise) {
		super(speed,effect,noise);
	}	
}

package day0802.ch13.lx.lx01;

public class InkpetPrinter extends Printer {

	@Override
	public void print() {
		System.out.println("喷墨打印机--打印速度"+this.getSpeed()+"，效果"+this.getEffect()+"，噪音"+this.getNoise());
	}
	
	//构造方法
	public InkpetPrinter() {}
	public InkpetPrinter(String speed, String effect, String noise) {
		super(speed,effect,noise);
	}	
}

package day0802.ch13.lx.lx01;

public class LaserPrinter extends Printer {

	@Override
	public void print() {
		System.out.println("激光打印机--打印速度"+this.getSpeed()+"，效果"+this.getEffect()+"，噪音"+this.getNoise());
	}
	
	//构造方法
	public LaserPrinter() {}
	public LaserPrinter(String speed, String effect, String noise) {
		super(speed,effect,noise);
	}	
}