覆盖和隐藏

Question

有人可以解释一下下面的代码为什么无效并给我错误的原因。

/* Java program to show that if static methods are redefined by 
   a derived class, then it is not overriding but hidding. */

// Superclass 
class Base { 

    // Static method in base class which will be hidden in subclass  
    public static void display() { 
        System.out.println("Static or class method from Base"); 
    } 

     // Non-static method which will be overridden in derived class  
     public void print()  { 
         System.out.println("Non-static or Instance method from Base"); 
    } 
} 

// Subclass 
class Derived extends Base { 

    // Static is removed here (Causes Compiler Error)  
    public void display() { 
        System.out.println("Non-static method from Derived"); 
    } 

    // Static is added here (Causes Compiler Error)  
    public static void print() { 
        System.out.println("Static method from Derived"); 
   } 

} 

Answer 1

这是一个错误，仅仅是因为它被定义为不允许。

您不能override a static method with an instance method：

  

（实例方法的：）如果重写的方法mA是静态方法，则是编译时错误。

或hide an instance method with a static method：

  

如果静态方法隐藏实例方法，则是编译时错误。