单例模式

概要

• 单例模式属于创建者类型
• 构造方法私有

• 提供一个公开的静态方法获取对象实例

  懒汉式

• 比较懒嘛，所以用的时候才创建实例对象

public class LazySingleton {
    private static LazySingleton singleton;
    private LazySingleton() {
    }
    public static LazySingleton getInstance() {
        if (singleton == null) {
            synchronized (LazySingleton.class) {
                if (singleton == null) {
                    singleton = new LazySingleton();
                }
            }
        }
        return singleton;
    }
}

饿汉式

• 饿汉，等不及了，所以是提前创建对象

public class HungrySingleton {
    private HungrySingleton singleton = new HungrySingleton();
    private HungrySingleton() {
    }
    public HungrySingleton getSingleton(){
        return singleton;
    }
}

静态内部类

public class InnerClassSingleton {
    private InnerClassSingleton() {
    }
    private static class Inner {
        private static final InnerClassSingleton singleton = new InnerClassSingleton();
    }
    public static InnerClassSingleton getInstance() {
        return Inner.singleton;
    }
}

枚举

• 枚举默认构造方法私有

public enum SingletonEnum {
    ONE,
    TWO,
    THREE;
    public static SingletonEnum getOne(){
        return ONE;
    }
    public static SingletonEnum getTwo(){
        return TWO;
    }
    public static SingletonEnum getThree(){
        return THREE;
    }
}