单例模式

[TOC]

单例模式的写法

懒汉式

不加同步

public class SingletonOne {

    private static SingletonOne sInstance;

    private SingletonOne() {
    }

    public static SingletonOne getInstance() {
        if (sInstance == null) {
            sInstance = new SingletonOne();
        }
        return sInstance;
    }
}

同步

public class SingletonTwo {

    private static SingletonTwo sInstance;

    private SingletonTwo() {
    }

    public synchronized static SingletonTwo getInstance() {
        if (sInstance == null) {
            sInstance = new SingletonTwo();
        }
        return sInstance;
    }
}

双重检查锁

public class SingletonThree {

    private static SingletonThree sInstance;

    private SingletonThree() {
    }

    public static SingletonThree getInstance() {
        if (sInstance == null) {
            synchronized (SingletonThree.class) {
                if (sInstance == null) {
                    sInstance = new SingletonThree();
                }
            }
        }
        return sInstance;
    }
}

volatile(推荐)

public class SingletonFour {

    private static volatile SingletonFour sInstance;

    private SingletonFour() {
    }

    public static SingletonFour getInstance() {
        if (sInstance == null) {
            synchronized (SingletonFour.class) {
                if (sInstance == null) {
                    sInstance = new SingletonFour();
                }
            }
        }
        return sInstance;
    }
}

饿汉式

public class SingletonFive {

    private static SingletonFive sInstance = new SingletonFive();

    private SingletonFive() {
    }

    public static SingletonFive getInstance() {
        return sInstance;
    }
}

静态内部类(推荐)

public class SingletonSix {

    private SingletonSix() {
    }

    public static SingletonSix getInstance() {
        return SingletonHolder.INSTANCE;
    }

    private static class SingletonHolder {
        public static final SingletonSix INSTANCE = new SingletonSix();

    }
}

枚举

public enum SingletonSeven {
    INSTANCE;
}

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