创建模式之单例模式

懒汉模式：

/**
 * @author yuyang
 * @DATE 2019/1/7 0007-8:59
 */
public class Singleton {
    private final static Singleton INSTANCE=null;
    private Singleton(){}
    public static synchronized Singleton getInstance(){
        if (INSTANCE==null){
            return  new Singleton();
        }else {
            return INSTANCE;
        }
    }
}

饿汉模式

public class Singleton {
    private final static Singleton INSTANCE = new Singleton();
    private Singleton(){}
    public static Singleton getInstance(){
        return INSTANCE;
    }
}

静态内部类

public class Singleton {
    private Singleton() {}
    private static class SingletonInstance {
        private static final Singleton INSTANCE = new Singleton();
    }
    public static Singleton getInstance() {
        return SingletonInstance.INSTANCE;
    }
}

同步方法

同步代码块

双重检查

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