Becoming Sanjuro

Fail again. Fail better.

A Note on Overriding in Java

Method overriding, in object oriented programming, is a language feature that allows a subclass or child class to provide a specific implementation of a method that is already provided by one of its superclasses or parent classes.

Can We Override Static Methods in Java?

Let’s try the following Java program to find out the answer.

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class Base {
  public static void foo() {
    System.out.println("Base foo");
  }
}
class Derived extends Base {
  public static void foo() {
    System.out.println("Derived foo");
  }
}
public class Main {
  public static void main(String[] args) {
    Base obj = new Derived();
    obj.foo();
  }
}

Output:

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Base foo

From the output, we know that the method according to the type of reference, instead of the one according to the object being referred, is called, which means it’s decided at compile time, instead of run time. So we can conclude that we can’t override static methods in Java.

Can We Override Final Methods in Java?

We can use final specifier to indicate that a method can’t be overridden by subclasses. Definitely the answer to the question is NO. Let’s try the following Java program.

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class Base {
  public final void foo() {
    System.out.println("Base foo");
  }
}
class Derived extends Base {
  public final void foo() {
    System.out.println("Derived foo");
  }
}
public class Main {
  public static void main(String[] args) {
    Base obj = new Derived();
    obj.foo();
  }
}

Compiler Error:

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Main.java:8: error: foo() in Derived cannot override foo() in Base
  public final void foo() {
                    ^
  overridden method is final
1 error

Can We Override Private Methods in Java?

According to Bruce Eckel’s Thinking in Java, private methods are implicitly final, which means the answer is still NO. Let’s try the following Java program.

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class Base {
  private void foo() {
    System.out.println("Base foo");
  }
}
class Derived extends Base {
  private void foo() {
    System.out.println("Derived foo");
  }
}
public class Main {
  public static void main(String[] args) {
    Base obj = new Derived();
    obj.foo();
  }
}

Compiler Error:

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Main.java:16: error: foo() has private access in Base
    obj.foo();
       ^
1 error