If you are implementing an interface in your java code, then you need to implement all its methods in a class. But if you want to use only add() method in your Addition class then implement three interfaces in your java code with three different methods.

Check the given code:

interface Maths1{
     void add();
}
interface Maths2{
     void sub();
}
interface Maths3{
     void mul();
}

class Addition implements Maths1 {
  public void add() {
    int a=6,b=4;
    int sum=a+b;
    System.out.println(sum);
  }
}
class Subtraction implements Maths2 {
  public void sub() {
    int a=6,b=4;
    int diff=a-b;
    System.out.println(diff);
  }
}
class Multiplication implements Maths3 {
  public void mul() {
    int a=6,b=4;
    int multiply=a*b;
    System.out.println(multiply);
  }
}
public class InterfaceExample{
  public static void main(String[]args){
      Addition a=new Addition();
      a.add();
      Subtraction s=new Subtraction();
      s.sub();
      Multiplication m=new Multiplication();
      m.mul();
     }
  }

thank you