代码复用的第三种：代理

这是继承与组合之间的中庸之道，因为我们将一个成员对象置于所要构造的类中（就像组合），但与此同时我们在新类中暴露了该成员对象的所有方法（就像继承）。代理就解决了这个问题，如下例: 继承： //Detergent.java class Cleanser { private String s = "Cleanser"; public void append(String a){ s += a; } public void dilute() { append(" dilute()"); } public void apply() { append(" apply()"); } public void scrub() { append(" scrub()"); } public String toString() { return s; } } public class Detergent extends Cleanser { public void scrub() { append(" Detergent.scrub()"); super.scrub(); } public void foam() { append(" foam()"); } public static void main(String[] args) { Detergent x = new Detergent(); x.dilute(); x.apply(); x.scrub(); x.foam(); System.out.print(x); }

代理：

//Detergent.java class Cleanser { private String s = "Cleanser"; public void append(String a){ s += a; } public void dilute(){ append(" dilute()"); } public void apply(){ append(" apply()"); } public void scrub(){ append(" scrub()"); } public String toString(){ return s; } } public class Detergent{ private Cleanser c=new Cleanser(); public void scrub(){ c.append(" Detergent.scrub()"); c.scrub(); } public void dilute(){ c.dilute(); } public void apply(){ c.apply(); } public void foam() { c.append(" foam()"); } public String toString(){ return c.toString(); } public static void main(String[] args) { Detergent x = new Detergent(); x.dilute(); x.apply(); x.scrub(); x.foam(); System.out.print(x); } } 

输出相同如下：

Cleanser dilute() apply() Detergent.scrub() scrub() foam()