java 完全解耦

只要有一个方法操作的是类而非接口,那么你就只能使用这个类及其子类,如果你想要将这个方法应用于不在此继承结构中的某个类,那么你就会触霉头,接口可以在很大程度上放宽这种限制,因此,我们可以编写可服用性更好的代码

//像本例这样,创建一个能够根据所传递的参数对象的不同而具有不同行为的方法,被称为策略设计
//策略就是传递进去的参数对象,它包含要执行的代码
//: interfaces/classprocessor/Apply.java
package object;
import java.util.*;
import static net.mindview.util.Print.*;

class Processor {
  public String name() {
    return getClass().getSimpleName();
  }
  Object process(Object input) { return input; }
}    

class Upcase extends Processor {
  String process(Object input) { // Covariant return
    return ((String)input).toUpperCase();
  }
}

class Downcase extends Processor {
  String process(Object input) {
    return ((String)input).toLowerCase();
  }
}

class Splitter extends Processor {
  String process(Object input) {
    // The split() argument divides a String into pieces:
    return Arrays.toString(((String)input).split(" "));//split()返回String[]数组
  }
}    

public class Apply {
  public static void process(Processor p, Object s) {
    print("Using Processor " + p.name());
    print(p.process(s));
  }
  public static String s =
    "Disagreement with beliefs is by definition incorrect";
  public static void main(String[] args) {
    process(new Upcase(), s);
    process(new Downcase(), s);
    process(new Splitter(), s);
  }
} /* Output:
Using Processor Upcase
DISAGREEMENT WITH BELIEFS IS BY DEFINITION INCORRECT
Using Processor Downcase
disagreement with beliefs is by definition incorrect
Using Processor Splitter
[Disagreement, with, beliefs, is, by, definition, incorrect]
*///:~

适配器设计模式,设配器的代码将接受你所拥有的接口,并产生你所需要的接口

//: interfaces/interfaceprocessor/FilterProcessor.java
package interfaces.interfaceprocessor;
import interfaces.filters.*;

class FilterAdapter implements Processor {
  Filter filter;
  public FilterAdapter(Filter filter) {  //FilterAapter 接受你拥有的接口Filer
    this.filter = filter;                //然后生成你需要的Processor接口的对象
  }
  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);
    Apply.process(new FilterAdapter(new HighPass(2.0)), w);
    Apply.process(
      new FilterAdapter(new BandPass(3.0, 4.0)), w);
  }
} /* Output:
Using Processor LowPass
Waveform 0
Using Processor HighPass
Waveform 0
Using Processor BandPass
Waveform 0
*///:~