1 单例模式 SingleTon

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经典模式

public class SingleTon {

private static SingleTon uniqueInstance;

//必须是私有
private SingleTon() {}
//线程不安全
public static SingleTon getInstance() {
if(uniqueInstance == null) {
uniqueInstance = new SingleTon();
}
return uniqueInstance;
}

//这里是其他的有用方法

}

改进：

1. 同步getInstance()：

public class SingleTon {

private static SingleTon uniqueInstance;

//必须是私有
private SingleTon() {}

public static synchronized SingleTon getInstance() {
if(uniqueInstance == null) {
uniqueInstance = new SingleTon();
}
return uniqueInstance;
}

//这里是其他的有用方法

}

2 急切实例化：

public class SingleTon {

private static SingleTon uniqueInstance = new SingleTon();

//必须是私有
private SingleTon() {}

public static SingleTon getInstance() {
return uniqueInstance;
}

//这里是其他的有用方法

}

3 双重检查加锁

public class SingleTon {

private static volatile SingleTon uniqueInstance;

//必须是私有
private SingleTon() {}

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

//这里是其他的有用方法

}

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