组合模式：将对象组合成树形结构以表示“部分-总体”的层次结构。
组合模式使得用户对单个对象和组合对象的使用具有一致性。
适用场合：当需求中是体现部分与总体层次的结构时，以及希望用户能够忽略组合对象与单个对象的不同，统一地使用组合结构中的全部对象时，就应该考虑用组合模式。
首先定义一个Componet抽象类
public abstract class Component {
protected String name;
public Component(String name){
this.name=name;
}
//抽象方法
public abstract void add(Component c);
public abstract void delete(Component c);
public abstract void dispaly(int depth);
}定义叶结点对象Leaf，继承Componet
public class Leaf extends Component {
public Leaf(String name) {
super(name);
}
@Override
public void add(Component c) {
System.out.println("can not add a leaf");
}
@Override
public void delete(Component c) {
System.out.println("can not delete a leaf");
}
@Override
public void dispaly(int depth) {
char[] ch=new char[depth];
for(int i=0;i<depth;i++){
ch[i]='-';
}
System.out.println(new String(ch)+name);
}
}结点定义枝结点Composite继承Component
public class Composite extends Component{
private List<Component> children=new ArrayList<Component>();
public Composite(String name) {
super(name);
}
@Override
public void add(Component c) {
children.add(c);
}
@Override
public void delete(Component c) {
children.remove(c);
}
@Override
public void dispaly(int depth) {
char[] ch=new char[depth];
for(int i=0;i<depth;i++){
ch[i]='-';
}
System.out.println(new String(ch)+name);
Iterator<Component> iterator=children.iterator();
while(iterator.hasNext()){
Component component=iterator.next();
component.dispaly(depth+2);
}
}
}client代码
public static void main(String[] args) {
//组合模式
Composite root=new Composite("root");
root.add(new Leaf("LeafA"));
root.add(new Leaf("LeafB"));
Composite comp=new Composite("Composite X");
comp.add(new Leaf("LeafXA"));
comp.add(new Leaf("LeafXB"));
root.add(comp);
Composite comp2=new Composite("Composite Y");
comp2.add(new Leaf("LeafXYA"));
comp2.add(new Leaf("LeafXYB"));
root.add(comp2);
root.add(new Leaf("LeafC"));
root.dispaly(1);
}结果：
-root
- - -LeafA
- - -LeafB
- - -Composite X
- - - - -LeafXA
- - - - -LeafXB
- - -Composite Y
- - - - -LeafXYA
- - - - -LeafXYB
- - -LeafC