8、Composite组合

属于结构型模式（共7种）

目的：
树状结构专用模式

类图

举例

abstract class Node {
    abstract public void p();
}
class LeafNode extends Node {
    String content;
    public LeafNode(String content) {this.content = content;}
    @Override
    public void p() {
        System.out.println(content);
    }
}
class BranchNode extends Node {
    List<Node> nodes = new ArrayList<>();
    String name;
    public BranchNode(String name) {this.name = name;}
    @Override
    public void p() {
        System.out.println(name);
    }
    public void add(Node n) {
        nodes.add(n);
    }
}
public class Main {
    public static void main(String[] args) {
        BranchNode root = new BranchNode("root");
        BranchNode chapter1 = new BranchNode("chapter1");
        BranchNode chapter2 = new BranchNode("chapter2");
        Node r1 = new LeafNode("r1");
        Node c11 = new LeafNode("c11");
        Node c12 = new LeafNode("c12");
        BranchNode b21 = new BranchNode("section21");
        Node c211 = new LeafNode("c211");
        Node c212 = new LeafNode("c212");
        root.add(chapter1);
        root.add(chapter2);
        root.add(r1);
        chapter1.add(c11);
        chapter1.add(c12);
        chapter2.add(b21);
        b21.add(c211);
        b21.add(c212);
        tree(root, 0);
    }
    static void tree(Node b, int depth) {
        for(int i=0; i<depth; i++) System.out.print("--");
        b.p();
        if(b instanceof BranchNode) {
            for (Node n : ((BranchNode)b).nodes) {
                tree(n, depth + 1);
            }
        }
    }
}