组合（Composition）指的是一个类的属性含有一个另一个类的引用，可以体现整体与部分、拥有的关系。
比如
public class Composition { public void function(){ System.out.println("Compostion's function is doing"); } } class getinto{ private Composition a; getinto(){ this.a = new Composition(); this.a.function(); System.out.println("getinto class is doing"); } public void function(){ System.out.println("getinto's function is doing"); } } class run{ public static void main(String[] args) { getinto a = new getinto(); a.function(); } }结果如下： Compostion’s function is doing getinto class is doing getinto’s function is doing
