静态方法和多态性
我有一个简单的问题，我无法找到一个很好的答案。为什么以下Java程序显示20？如果可能的话，我更喜欢详细的答复。
class Something{
public int x;
public Something(){
x=aMethod();
}
public static int aMethod(){
return 20;
}
}
class SomethingElse extends Something{
public static int aMethod(){
return 40;
}
public static void main(String[] args){
SomethingElse m;
m=new SomethingElse();
System.out.println(m.x);
}
}
I have a simple question that I just can't figure out a good answer for. Why does the following Java program display 20? I would prefer a detailed response if possible please.
class Something{
public int x;
public Something(){
x=aMethod();
}
public static int aMethod(){
return 20;
}
}
class SomethingElse extends Something{
public static int aMethod(){
return 40;
}
public static void main(String[] args){
SomethingElse m;
m=new SomethingElse();
System.out.println(m.x);
}
}
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评论（3）
因为多态性仅适用于实例方法。
static方法amethod在此调用amethod在> something中声明。Because polymorphism only applies to instance methods.
The
staticmethodaMethodinvoked hererefers to the
aMethoddeclared inSomething.静态方法的继承的起作用与非静态方法不同。特别是，超类静态方法并未被子类覆盖。静态方法调用的结果取决于它被调用的对象类。变量x是在某物对象创建期间创建的，因此，静态方法被调用以确定其值。
考虑以下代码：
它将正确打印40、20，因为每个对象类都调用自己的静态方法。 java文档在隐藏静态方法部分中描述了这种行为。
The inheritance for static methods works differently then non-static one. In particular the superclass static method are NOT overridden by the subclass. The result of the static method call depends on the object class it is invoke on. Variable x is created during the Something object creation, and therefore that class (Something) static method is called to determine its value.
Consider following code:
It will correctly print the 40, 20 as each object class invokes its own static method. Java documentation describes this behavior in the hiding static methods part.
因为在类的类中声明了int x。当您制作
something emavelse对象时，您首先制作themess对象（必须设置x，然后使用amethod（）从<<代码>某物而不是something oferes（因为您正在创建themings））。这是因为Amethod（）是静态的，并且多态性对于静态方法不起作用。然后，当您从M中打印X时，您打印20，因为您从未更改x的值。Because int x is declared in the class
Something. When you make theSomethingElseobject, you first make aSomethingobject (which has to set x, and it uses theaMethod()fromSomethinginstead ofSomethingElse(Because you are creating aSomething)). This is because aMethod() is static, and polymorphism doesn't work for static methods. Then, when you print the x from m, you print 20 since you never changed the value of x.