单例模式的详情

17-11-16 来源：[db:作者]

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懒汉式：懒汉式单例类.在第一次调用的时候实例化自己

public class Singleton {
    private static Singleton mInstance = null;

    private Singleton() {
    }

    public static Singleton getInstance() {
        if (null == mInstance) {
            mInstance = new Singleton();
        }
        return mInstance;
    }
}

恶汉式：饿汉式单例类.在类初始化时，已经自行实例化

public class Singleton {
    private static Singleton mInstance = new Singleton();

    private Singleton() {
    }

    public static Singleton getInstance() {
        return mInstance;
    }
}

在getInstance方法上加同步锁

public class Singleton {
    private static Singleton mInstance = null;

    private Singleton() {
    }

    public static synchronized Singleton getInstance() {
        if (null == mInstance) {
            mInstance = new Singleton();
        }
        return mInstance;
    }
}

双重检查锁定

public class Singleton {
    private static Singleton mInstance = null;

    private Singleton() {
    }

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

静态内部类

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

    private Singleton() {
    }

    public static final Singleton getInstance() {
        return LazyHolder.INSTANCE;
    }
}

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