问题
Why is the output different in the below case even when, the variable has been overridden?
public class A {
int a = 500;
void get() {
System.out.println("a is " + this.a);
}
}
public class B extends A {
int a = 144;
}
public class mainmethod {
public static void main(String args[]) {
B ob = new B();
System.out.println("a is " + ob.a);
ob.get();
}
}
回答1:
There is no such thing as overridden variables. B actually has two instance variables named a: one it declares and another it inherits. See this:
B ob = new B();
System.out.println("B.a is " + ob.a);
System.out.println("A.a is " + ((A)ob).a);
Inside a B's instance method you can write super.a or ((A)this).a to access the parent's variable.
回答2:
When doing ob.a, you get the variable int a from your ob object, which is object of the class B.
However, when you do ob.get();, you are calling the get()-method from class A, because there is no get() in B, which - as you wrote - uses this.a, which would be the int a of class A in that case.
回答3:
No the variable is not overridden.
ob.a
print the a variable of B class.
ob.get()
searches for the get method in B class.when it does not gets there it then searches the parent class and executes it.
来源：https://stackoverflow.com/questions/32350894/why-is-the-output-different-in-the-two-cases