Java Class and Interface Name Collision

Question

interface A {
  void print();
}

class A implements A {
  public void print() {
    System.out.println("Hello");
  }
  public static void main(String args[]) {
    A a=new A();
    a.print();
  }
}

When i am using this code then it is saying "duplicate class:A". Why so? Can I not have same class and interface name

Answer 1

You can't have a class and an interface with the same name because the Java language doesn't allow it.

First of all, it's ambiguous. If you declare a variable like this:

A a;

What is the type of that variable? Is it the class, or the interface?

Second, compiled Java code is stored in .class files named after the class or interface defined in the file. An interface named A and a class named A would both compile to a file named A.class. You can't have two files with the same name in the same folder.

The error message says "duplicate class" because Java internally treats an interface as a special kind of class.