HENNG

Java设计模式 - Singleton

Java 设计模式 单例模式 Singleton

懒汉（线程安全）

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//懒汉
public class Singleton {
	private static Singleton singleton;

	private Singleton() {

	}

	public static synchronized Singleton getSingleton() {
		if (singleton == null) {
			singleton = new Singleton();
		}

		return singleton;
	}
}

饿汉

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//饿汉
public class Singleton {
	private static final Singleton singleton = new Singleton();

	private Singleton () {

	}

	public static Singleton getSingleton() {
		return singleton;
	}
}

静态内部类

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//静态内部类
public class Singleton {
	private static class SingletonHolder {
		private static final Singleton singleton = new Singleton();
	}

	private Singleton() {

	}

	public static Singleton getSingleton() {

		return SingletonHolder.singleton;
	}
}

枚举

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//枚举
public enum Singleton {
	INSTANCE;

	public void whateverMethod() {

	}
}

double-lock

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//double-lock
public class Singleton {
	private volatile static Singleton singleton;

	private Singleton() {

	}

	public static Singleton getSingleton() {
		if (singleton == null) {
			synchronized(Singleton.class) {
				if (singleton == null) {
					singleton = new Singleton();
				}
			}
		}

		return singleton;
	}
}