Java 如何从派生类外部调用超级方法（即：toString()）
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How to call a super method (ie: toString()) from outside a derived class
提问by fedevo
existantial question
存在的问题
if i have a class hierarchy like:
如果我有一个类层次结构，如：
public class TestSuper {
public static class A {
@Override
public String toString() { return "I am A"; }
}
public static class B extends A {
@Override
public String toString() { return "I am B"; }
}
public static void main(String[] args) {
Object o = new B();
System.out.println( o ); // --> I am B
// ?????? // --> I am A
}
}
From the main method, is it possible to call the toString of A when the instance is of type B ???
从 main 方法中，当实例是 B 类型时，是否可以调用 A 的 toString ？？？
of course, something like o.super.toString() doesn't compile ...
当然，像 o.super.toString() 这样的东西不能编译......
采纳答案by Jon Skeet
You can't, and very deliberately so: it would break encapsulation.
你不能，而且是故意这样做的：它会破坏封装。
Suppose you had a class which used a method to validate input by some business rules, and then call the superclass method. If the caller could just ignore the override, it would make the class pretty much pointless.
假设您有一个类，它使用一种方法来验证某些业务规则的输入，然后调用超类方法。如果调用者可以忽略覆盖，它将使该类变得毫无意义。
If you find yourself needing to do this, revisit your design.
如果您发现自己需要这样做，请重新审视您的设计。
回答by weekens
It's not possible, because toString() of A is overriden by B (I guess, you meant "class B extends A").
这是不可能的，因为 A 的 toString() 被 B 覆盖（我猜，你的意思是“B 类扩展 A”）。
回答by mrK
You can just add another method to call the super string. Something like:
您可以添加另一个方法来调用超级字符串。就像是：
public string getSuperString(){
return super.toString();
}
回答by RamonBoza
In your code it is not possible, in case B extends A
在您的代码中这是不可能的，以防 B 扩展 A
public class TestSuper {
public static class A {
@Override
public String toString() { return "I am A"; }
}
public static class B {
@Override
public String toString() { return "I am B"; }
}
public static void main(String[] args) {
B b = new B();
System.out.println( b ); // --> I am B
A a = (A)b;
System.out.println( a );
}
}
回答by Peter Lawrey
You can either
你可以
Add a method to A or B which you call instead.
// to A public String AtoString() { return toString(); } // OR to B public String AtoString() { return super.toString(); }Inline the code of A.toString() to where it is "called"
// inlined A.toString() String ret = "I am A"; System.out.println( ret );
将方法添加到您调用的 A 或 B。
// to A public String AtoString() { return toString(); } // OR to B public String AtoString() { return super.toString(); }将 A.toString() 的代码内联到它被“调用”的地方
// inlined A.toString() String ret = "I am A"; System.out.println( ret );
Both these options suggest a poor design in your classes, however sometimes you have existing classes you can only change in limited ways.
这两个选项都表明您的课程设计不佳，但是有时您有现有的课程，您只能以有限的方式进行更改。
