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单例模式总结

2024-07-23 08:40:00   210人阅读

即时加载

public class Singleton {
	private static final Singleton uniqueInstance = new Singleton();

	private Singleton() {
	}

	public static Singleton getInstance() {
		return uniqueInstance;
	}
}
延时加载——双重检测枷锁

注意volatile关键字

public class Singleton {
	private volatile static Singleton uniqueInstance;

	private Singleton() {
	}

	public static Singleton getInstance() {
		if (uniqueInstance == null) {
			synchronized (Singleton.class) {
				if (uniqueInstance == null) {
					uniqueInstance = new Singleton();
				}
			}
		}
		return uniqueInstance;
	}
}
延时加载——内部静态类

内部静态类在第一次被引用时加载，是线程安全的

public class Singleton {
	private Singleton() {
	}

	public static Singleton getInstance() {
		return Nested.uniqueInstance;
	}

	static class Nested {
		private static final Singleton uniqueInstance = new Singleton();
	}
}
单例模式序列化

注意实现readResolve方法，并且所用带有对象引用的实例域都必须声明为transient，详见《Effective Java》第77条。

import java.io.Serializable;

public class Singleton implements Serializable {
	private static final Singleton uniqueInstance = new Singleton();

	private transient String element = "singleton";

	private Singleton() {
	}

	public static Singleton getInstance() {
		return uniqueInstance;
	}

	private Object readResolve() {
		return uniqueInstance;
	}
}
枚举类

单例的最佳实现方法，提供序列化机制，防止多次实例化，并且线程安全。

public enum Singleton {
	INSTANCE;

	// elements & methods
}





单例模式总结


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