在类中,与超类中的字段同名的字段会隐藏超类的字段。
public class Test {
public static void main(String[] args) {
Father father = new Son();
System.out.println(father.i); //why 1?
System.out.println(father.getI()); //2
System.out.println(father.j); //why 10?
System.out.println(father.getJ()); //why 10?
System.out.println();
Son son = new Son();
System.out.println(son.i); //2
System.out.println(son.getI()); //2
System.out.println(son.j); //20
System.out.println(son.getJ()); //why 10?
}
}
class Son extends Father {
int i = 2;
int j = 20;
@Override
public int getI() {
return i;
}
}
class Father {
int i = 1;
int j = 10;
public int getI() {
return i;
}
public int getJ() {
return j;
}
}
有人可以帮我解释一下结果吗?
在 Java 中,字段不是多态的。
Father father = new Son();
System.out.println(father.i); //why 1? Ans : reference is of type father, so 1 (fields are not polymorphic)
System.out.println(father.getI()); //2 : overridden method called
System.out.println(father.j); //why 10? Ans : reference is of type father, so 2
System.out.println(father.getJ()); //why 10? there is not overridden getJ() method in Son class, so father.getJ() is called
System.out.println();
// same explanation as above for following
Son son = new Son();
System.out.println(son.i); //2
System.out.println(son.getI()); //2
System.out.println(son.j); //20
System.out.println(son.getJ()); //why 10?
根据覆盖和隐藏方法
调用的隐藏方法的版本取决于它是从超类还是子类调用。
即当您通过超类引用调用在子类中重写的方法时,将调用超类方法并访问超类成员。
这解释了以下内容,因为所使用的参考是超类的:
System.out.println(father.i); //why 1?
System.out.println(father.j); //why 10?
System.out.println(father.getJ()); //why 10?
同样适用于以下情况:
System.out.println(son.getJ()); //why 10?
由于
getJ()
未在 Son
中定义,因此会调用 Father
版本,该版本会看到在 Father
类中定义的成员。
如果您阅读了隐藏字段;他们特别不推荐这样的编码方法
一般来说,我们不建议隐藏字段,因为这会使代码难以阅读。