1.享元模式(Flyweight)定义:运用共享技术有效地支持大量细粒度的对象

class Tree{
    private final String name;  //final初始后不可再变化,避免多线程下数据安全问题
    private final String data;  //final初始后不可再变化,避免多线程下数据安全问题
    public Tree(String name,String data){
        this.name = name;
        this.data = data;
        System.out.println(name+" created");
    }
}
class TreeInstance{
    public int x;
    public int y;
    public Tree tree;
    public TreeInstance(int x,int y,Tree tree){
        this.x = x;
        this.y = y;
        this.tree = tree;
    }
}
class TreeFactory{
    public static Map<String,Tree> mapTree = new ConcurrentHashMap<>();
    public static Tree getTree(String treeName,String data){
        if(mapTree.containsKey(treeName)){
            return mapTree.get(treeName);
        }
        Tree tree = new Tree(treeName,data);
        mapTree.put(treeName,tree);
        return tree;
    }
}
public class Flyweight {
    public static void main(String[] args) {
        //在位置点6，8种一棵tree1树
        TreeInstance treeInstance1 = new TreeInstance(6,8,TreeFactory.getTree("tree1","data1"));
        //在位置点10，18种一棵tree1树，此时会返回一棵相同的树，即treeNode1和treeNode2共享一颗同样的树，只是位置不一样，如游戏场景下可以节省很多相同的树创建多个相同的对象，节省内存空间
        TreeInstance treeInstance2 = new TreeInstance(10,18,TreeFactory.getTree("tree1","data1"));
        //当然这里也可以创建其它类型的树，并传入树的相关data信息
        TreeInstance treeInstance3 = new TreeInstance(20,28,TreeFactory.getTree("tree2","data2"));
    }
}

应用场景：
大量的重复对象使用

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

JDK源码中的应用
1String,Integer,Long…
2com.sun.org.apache.bcel.internal.generic.InstructionConstants