Java单例模式几种实现方式

单例模式在很多种语言中都有用到并且有自己的实现方式.

这里列举几种Java的单例模式实现方法:

1. 枚举类型

2. 懒汉模式-内部类实现

3. 懒汉模式-双重检查

// 1: 枚举类型
public enum SingletonEnum {
INSTANCE;
}

// 2: 勤快的汉子---你威武雄壮! 在加载类时就实例化对象, 利用Java的类加载的同步机制, 解决同步问题
class SingletonInLoad {
private static SingletonInLoad instance;

private SingletonInLoad() {};

public static SingletonInLoad getInstance() {
return instance;
}
}

// 3: 懒汉模式-内部类实现
class SingletonInner {
private SingletonInner() {}

private static class SingletonInnerHolder {
static final SingletonInner Instance = new SingletonInner();
}

public SingletonInner getInstance() {
return SingletonInner.SingletonInnerHolder.Instance;
}
}

// 4: 懒汉模式-双重检查
class SingletonDoubleCheck {
private static volatile SingletonDoubleCheck instance;

private SingletonDoubleCheck() {}

public SingletonDoubleCheck getInstance() {
if (instance == null) {
synchronized (SingletonDoubleCheck.class) {
if (instance == null) {
instance = new SingletonDoubleCheck();
}
}
}
return instance;
}
}