單例模式是類級別的，一個類只能有一個物件例項；

享元模式是物件級別的，可以有多個物件例項，多個變數引用同一個物件例項；

享元模式主要是為了節約記憶體空間，提高系統性能，而單例模式主要為了可以共享資料；

1:單例模式

public class Singleton {
    // 我來寫一個單例模式  懶漢式
    private static Singleton singleton;
    private Singleton(){}
    
    public static synchronized Singleton getSingleton(){
        if(singleton==null){
            singleton=new Singleton();
        }
        return singleton;
    }
    public static void main(String[] args) {
        Singleton instance1 = Singleton.getSingleton();
        Singleton instance2 = Singleton.getSingleton();
        System.out.println(instance1==instance2);
    }
}

2:享元模式

//享元模式是多個變數公用一個物件例項  大大節約了記憶體空間  提高了系統性能  String類是final型別 就是使用了享元模式
//資料庫連線池 執行緒池也是享元模式的應用
public abstract class Flyweight {
    // 享元模式 享元抽象類
    public abstract void operation();
}

//具體類 享元實現類
public class CreateFlyweight extends Flyweight {

    private String str;

    public CreateFlyweight(String str) {
        this.str = str;
    }

    @Override
    public void operation() {
        // TODO Auto-generated method stub
        System.out.println("Create---Flyweight:" + str);
    }

    public static void main(String[] args) {
        Flyweight flyweight = new CreateFlyweight("fanck");
        flyweight.operation();
    }

}

//工廠方法類 維護一個物件儲存池 享元工廠類
public class FlyweightFactory {
    private Hashtable flyweights = new Hashtable();

    public FlyweightFactory() {
    };

    public Flyweight getFlyweight(Object obj) {
        Flyweight flyweight = (Flyweight) flyweights.get(obj);
        if (flyweight == null) {
            flyweight = new CreateFlyweight((String) obj);
            flyweights.put(obj, flyweight);
        }
        return flyweight;
    }

    public int getFlyweightSize() {
        System.out.println("flyweights:"+flyweights);
        return flyweights.size();
    }

    public static void main(String[] args) {
        FlyweightFactory flyweightFactory = new FlyweightFactory();
        Flyweight fly1 = flyweightFactory.getFlyweight("abc");
        Flyweight fly2 = flyweightFactory.getFlyweight("b");
        Flyweight fly3 = flyweightFactory.getFlyweight("abc");
        Flyweight fly4 = flyweightFactory.getFlyweight("ef");
        Flyweight fly5 = flyweightFactory.getFlyweight("ef");
        Flyweight fly6 = flyweightFactory.getFlyweight("ef");
        fly1.operation();
        fly2.operation();
        fly3.operation();
        fly4.operation();
        fly5.operation();
        fly6.operation();
        System.out.println(flyweightFactory.getFlyweightSize());
    }
}