java - 急切初始化单例 vs 惰性初始化单例

Question

在思考单例设计模式时，我在急切初始化单例和静态 block 初始化单例模式之间徘徊。假设急切初始化单例类代码是 -

public class EagerInitSingleton {

    private static final EagerInitSingleton instance = new EagerInitSingleton();

    //private constructor
    private EagerInitSingleton(){}

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

和静态 block 单例类代码如下-

public class StaticBlockSingleton {

    private static StaticBlockSingleton instance;

    private StaticBlockSingleton(){}

    //static block initialization for exception handling
    static{
        try{
            instance = new StaticBlockSingleton();
        }catch(Exception e){
            throw new RuntimeException("Exception occured in singleton instance");
        }
    }

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

我们不要在这里谈论惰性初始化和线程安全。我想弄清楚 Static block singleton 中的两个静态 block 在这里有何不同。

Answer 1

没有区别。

private static final EagerInitSingleton instance = new EagerInitSingleton();

相当于

private static final EagerInitSingleton instance;

static {
    instance = new EagerInitSingleton();
}