No setter methods in interface

Question

I've a concrete class A that implements an interface B.

B ref = new A();

Code :

public interface B{
  public abstract String[] getWords();
}

public class A implements B {
  private String[] words = new String[] {};
  public void setWords(String[] words){
    this.words = words;
  }
  public String[] getWords(){
    return this.words;
  }
 }

In the interface B, I've only getter method but no setter method though the class A has it.

So when I do this : B ref = new A();, will this code work and how will I set words?

Answer 1

You won't be able to call setWords on ref if it is defined as B ref = ....

This is one of the cases where you need to use the exact type when declaring the variable (or use a cast):

A ref = new A();

Alternatively:

• you could create an interface C that extends B and contains both methods and have A implement C.
• you could provide a constructor in A that takes a String[] words argument to initialise your words field, and not provide a setter at all.

I would personally favour the latter option:

public class A implements B {

    private final String[] words;

    public A(String[] words) {
        this.words = words;
    }

    public String[] getWords() {
        return this.words;
    }
}