接口的使用——适配器设计模式

/////////在电子滤波器的例子中，类库是被发现而非创建的，在这些情况下，可以使用适配器设计模式，适配器(FilterAdapter)中的代码将接受你所拥有的接口(Processor)，并产生你所需要的接口，用组合将基类(Filter)与接口(Processor)联系起来。

class Waveform{
private static long counter;
private final long id=counter++;
public String toString(){ return "Waveform"+id; }
}

class Filter{
public String name(){
  return getClass().getName();
}
public Waveform process(Waveform input){ return input; }
}

class LowPass extends Filter{
double cutoff;
public LowPass(double cutoff){ this.cutoff=cutoff; }
public Waveform process(Waveform input){ return input; }
}

class HighPass extends Filter{
double cutoff;
public HighPass(double cutoff){ this.cutoff=cutoff; }
public Waveform process(Waveform input){ return input; }
}

class BandPass extends Filter{
double lowCutoff,highCutoff;
public BandPass(double lowCutoff,double highCutoff){ this.lowCutoff=lowCutoff; this.highCutoff=highCutoff; }
public Waveform process(Waveform input){ return input; }
}



interface Processor{
String name();
Object process(Object input);
}

class Apply{
public static void process(Processor p,Object s){
  System.out.print("Using Processor\n"+p.name()+"\n");
  System.out.print(p.process(s)+"\n");
}
}

//////////适配器

class FilterAdapter implements Processor{
Filter filter;/////////////用到了代理

public FilterAdapter(Filter filter){ this.filter=filter; }
public String name(){ return filter.name(); }
public Waveform process(Object input){
  return filter.process((Waveform)input);
}
}

public class FilterProcessor {
public static void main(String[] args){
  Waveform w=new Waveform();
  Apply.process(new FilterAdapter(new LowPass(1.0)), w);

//////////////////分析这句代码：初始化最里面的对象，一步一步向外扩张调用需要的方法。
  Apply.process(new FilterAdapter(new HighPass(2.0)), w);
  Apply.process(new FilterAdapter(new BandPass(3.0,4.0)), w);
}
}