Question

在下面的给定代码中，我的行为模棱两可：

public class Main {

    public static void main(String[] args) {

        labo(Main::myFunction);
        labo(Main::myFunctionWithNoArgs);//Compiletime exception!!!
        labo(String::toUpperCase);//Compiled line!!!
    }

    public static void labo(Function<String,String> function){
        System.out.println(function.apply("test"));
    }

    public static String myFunction(String arg){
        return arg;
    }

    public static String myFunctionWithNoArgs(){
        return "";
    }
}

我的问题是：我不明白为什么我没有得到arg String :: toUpperCase的编译时异常，而Main :: myFunctionWithNoArgs却没有，即使toUpperCase（）是与myFunctionWithNoArgs（）一样没有args的方法。 / p>

Answer 1

在这种情况下，

protected void fireActionPerformed(ActionEvent e) { // Dispatch a copy of the given ActionEvent in order to // set the source and action command correctly. ActionEvent ae = new ActionEvent( this, e.getID(), getActionCommand(), e.getWhen(), e.getModifiers()); ActionListener[] listeners = getActionListeners(); for (int i = 0; i < listeners.length; i++) //no way to prematurely terminate this loop listeners[i].actionPerformed(ae); }等效于String::toUpperCase，即它是从s -> s.toUpperCase()到String的函数。

此处的“参数”是方法的接收者，即String下注转换为大写。

Answer 2

如果将其写为lambda可能更有意义：

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                    <div class="accordian-item">
                        <div class="accordian-title">TITLE<span class="accordian-title-icon"></span></div>
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                            <p>This is a sentence.</p>
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函数ref为arg的歧义行为

2 个答案: