java - 由于类没有状态，因此无需延迟初始化

Question

在我的java学习之旅中，我遇到了带有以下注释的代码:

/**
 * Singleton instance - no need to lazy init as the class holds no state.
 */
public static final SuperParentMarshaller instance = new SuperParentMarshaller ();

这是什么意思？这会是一堂什么样的课呢？其目的是？

提前谢谢您。

Answer 1

这是您提到的急切初始化。在请求该对象之前，该对象已经初始化。使其变得惰性意味着该对象将在第一次调用时进行初始化。这是一个单一的设计模式。整个应用程序中只会有一个该类的对象。

// eager loading of INSTANCE    
public class Singleton
{
//initailzed during class loading
private static final Singleton INSTANCE = new Singleton();

//to prevent creating another instance of Singleton
private Singleton(){}

public static Singleton getSingleton(){
    return INSTANCE;
}
}

延迟初始化是:

// lazy initialization
public class Singleton
{
//initailzed during class loading
private static final Singleton INSTANCE;

//to prevent creating another instance of Singleton
private Singleton(){}

public static Singleton getSingleton(){
    // object will be initialized on it's first call.
    if(INSTANCE == null)
        INSTANCE = new Singleton();
    return INSTANCE;
}
}