'toString'这里是怎么解决的？

Question

下面的interface I隐含了class Object的public方法作为抽象成员。其中之一是 toString()

interface I{ 
   void test(int i);
   //implicitly has abstract members matching every public method of 'class Object'
   // one of them is toString()
}

下面class W继承class Objectpublic方法，其中之一是toString,

class W implements I{
    public static void main(String[] args){
       I w = new W();
       w.toString();   //How toString() method is resolved here?
    }
}

As both, super interface(I) and super class(Object) of class W 有toString()方法，

javac如何在编译时解析w.toString()？我了解到这里使用了invokevirtual指令。

jvm如何在运行时解析w.toString()？

Answer 1

interface 不会覆盖方法。

您的 class 也没有覆盖方法 toString()。您必须重写方法 toString() 才能覆盖它。

所以简单的就叫实现toString()的superclass Object.

Answer 2

接口不会覆盖任何 class 的方法。当您使用 toString() 方法时，默认的 toString() 从 Object class 执行，因为您的 class W 扩展自 Object.如需更多说明，请覆盖 class W 中的 toString() 方法。

@Override
public String toString() {

    return "Yo, baby! M here!";
}

那么输出将是：

Yo, baby! M here!

Answer 3

接口没有任何超级 class 甚至对象 class 也没有，例如

public class Main {
  public static void main(String[] argv) throws Exception {

    Class cls = java.lang.Cloneable.class;
    Class sup = cls.getSuperclass(); // will return null
  }
}

因此接口永远不会覆盖对象的方法class。

When an interface has no direct SuperInterface, it will create abstract public method for all those public methods present in the Object class.

Answer 4

因为该方法是在接口类型 I 类型的表达式上调用的，所以字节码将包含对应方法的 invokeinterface 指令。

在运行时，调用的方法将被确定

Let C be the class of objectref. The actual method to be invoked is selected by the following lookup procedure:

If C contains a declaration for an instance method with the same name and descriptor as the resolved method, then it is the method to be invoked.

Otherwise, if C has a superclass, a search for a declaration of an instance method with the same name and descriptor as the resolved method is performed, starting with the direct superclass of C and continuing with the direct superclass of that class, and so forth, until a match is found or no further superclasses exist. If a match is found, then it is the method to be invoked.

Otherwise, if there is exactly one maximally-specific method (§5.4.3.3) in the superinterfaces of C that matches the resolved method's name and descriptor and is not abstract, then it is the method to be invoked.

在您的例子中，objectref 是对 W 类型对象的引用。 W不包含与已解析方法具有相同名称和描述符的实例方法的声明。因此，我们检查 W、Object 的超类。 Object有没有有这样的方法。因此调用该方法。

'toString'这里是怎么解决的？

How 'toString' get resolved here?

java

overriding