如何从匿名内部类调用特定的父构造函数？ [英] How to call a specific parent constructor from anonymous inner class?

问题描述

好的，所以我知道一个匿名内部类是隐式地扩展父类或实现一个接口，因此超类的构造函数将需要被调用。但是，我不知道如何创建一个构造函数的匿名类（如果这是可能的），没有定义一个构造函数我不知道如何调用super（）！这是我的练习代码：

Ok, So I know that an anonymous inner class is either implicitly extending a parent class or implementing an interface, and therefore a constructor of the superclass will need to be called. However, I'm not sure how to create a constructor for the anonymous class (if this is possible) and without defining a constructor I'm not sure how to make calls to super()! Here is my practice code:

public class AnonymousConstructor {
    public static void main(String[] args) {
        //I'm not sure how to explicitly call one of the arg super constructors
        MyBob my = new MyBob() {
            //I would like to do something like this super("String"); or      
            //super("String", "String");
        };

    }
}

class MyBob extends Thread {
    MyBob() {
        System.out.println("No arg constructor");
    }
    MyBob(String a) {
        System.out.println("Arg constructor");
    }
    MyBob(String a, String b) {
        System.out.println("2 arg constructor");
    }
    public void run() {
        System.out.println("Outer");
    }
}

我担心的是，如果你尝试匿名类从没有一个无arg的构造函数的代码将在编译时失败的类，因为没有办法传递参数到超构造函数。

My concern is that if you try to make an anonymous class from a class that doesn't have a no-arg constructor that the code will fail at compile time because there is no way to pass an argument to the superconstructor. Is this a valid concern, and if so, is there a way around this?

推荐答案

您不能为构造函数定义构造函数匿名类（部分），但您可以通过向 new 调用提供参数来控制调用哪个超级构造函数：

You can't define a constructor for an anonymous class (part of the language specification), but you can control which super constructor is called by simply providing arguments to the new call:

MyBob my = new MyBob("foo") { // super(String) is called
    // you can add fields, methods, instance blocks, etc, but not constructors
}

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