享元模式

模式定义:运用共享技术有效地支持大量细粒度的对象。

优点：如果系统有大量类似的对象，可以节省大量的内存及CPU资源。

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class TreeNode{
    private int x;
    private int y;
    private Tree tree;
    public TreeNode(int x, int y, Tree tree) {
        this.x = x;
        this.y = y;
        this.tree = tree;
    }
    public int getX() {
        return x;
    }
    public int getY() {
        return y;
    }
    public Tree getTree() {
        return tree;
    }
}

class Tree{
    private final String name;
    private final  String data;
    public Tree(String name, String data) {
        System.out.println("name:"+name+"tree   created. ");
        this.name = name;
        this.data = data;
    }
    public String getName() {
        return name;
    }
    public String getData() {
        return data;
    }
}

class TreeFactory{
    private static Map<String,Tree> map = new ConcurrentHashMap<>();
    public static Tree getTree(String name,String data){
        if (map.containsKey(name)){
            return map.get(name);
        }
        Tree tree = new Tree(name, data);
        map.put(name,tree);
        return tree;
    }
}

JDK源码中的应用：

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String,Integer,Long...
com.sun.org.apache.bcel.internal.generic.InstructionConstants;