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
*///:~