java - 接口(interface)转换难题

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Java: Casting a class to an unrelated interface
                                
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                            Casting between Interfaces and Classes
                                
                                    （2个答案）
                                
                        
                        
                            Why does it compile when casting to an unrelated interface?
                                
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                                2年前关闭。
            
                    
我对这个（适当的）简单的转换示例有一个尴尬的问题。请你帮助我好吗？

public class Example1 {

interface ParentIf{}
interface ChildIf extends ParentIf {}
interface OtherIf {}

class ParentCl {}
class ChildCl extends ParentCl {}
class OtherCl {}

    public static void main(String[] args) {
        ChildIf cI = null;
        ParentIf pI = null;
        OtherIf oI = null;
        ChildCl cC = null;
        ParentCl pC = null;
        OtherCl oC = null;

        cI = (ChildIf)oI; //case1 - fine

        cC = (ChildCl)oC; //case2 - inconvertible types

        cI = (ChildIf)oC; //case3 - fine
    }
}

但是更尴尬的是，我不知道为什么其他两个陈述还可以。

我看不到OtherIf和ChildIf之间的任何连接。那么当case1的两个接口之间没有“扩展”时，如何将OtherIf强制转换为ChildIf？

最佳答案

cI = (ChildIf)oI;

很好，因为oI可以是同时实现ChildIf和OtherIf的类的实例。

cI = (ChildIf)oC;

很好，因为oC可能是扩展OtherClass的类的实例，而anec实现了ChildIf。