java單例模式怎么實現

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Java 中單例模式的實現方法有以下幾種：

懶漢式（線程不安全）：

public class Singleton {
private static Singleton instance;
private Singleton() {}
public static Singleton getInstance() {if (instance == null) {instance = new Singleton();
}
return instance;
}
}

懶漢式（線程安全）：

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

餓漢式：

public class Singleton {private static final Singleton instance = new Singleton();
private Singleton() {}
public static Singleton getInstance() {return instance;}
}

雙重檢查鎖定（Double-Checked Locking）：

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

靜態(tài)內部類：

public class Singleton {
private static class SingletonHolder {private static final Singleton INSTANCE = new Singleton();
}
private Singleton() {}
public static Singleton getInstance() {return SingletonHolder.INSTANCE;}
}

以上是幾種常見的單例模式實現方法，每種方法都有各自的優(yōu)缺點，可以根據具體需求選擇適合的實現方法。

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