Java – type A has defined an error

I tried to search for a solution, but I found that I didn't know how to apply it in this case Please help me correct my code

package Exercise;

public class Ex11_11 {
public static void main(String[] args) {
    A a = new A(3);
    }
}

class A extends B { // type A is already defined,A has a red underline
    public A (int t) {
    System.out.println("A's constructor is invoked");
    }
}

class B { // type B is already defined,B has a red underline
    public B () {
        System.out.println("B's constructor is invoked");
    }  
}

Solution

Well, the first thing to check is whether there is another class called A. in your file or the same package