In an immutable class, why are fields marked as private?

Question

What is the advantage of creating fields when creating an immutable class?

I saw why when creating an immutable class, fields are declared private? but I didn’t understand anything from this post.

Can someone explain the same to me?

Answer 1

The best way to explain is an example:

  public class Immutable {
     private final char[] state = "Hi Mom".getChars();

     public char[] getState() {
         return state.clone();
     }
  }

Here we have a properly encapsulated, immutable class. Nothing can change the state (modulo unpleasant reflective tricks).

Now allows JUST to change access to the field:

  public class Immutable {
     public final char[] state = "Hi Mom".getChars();

     public char[] getState() {
         return state.clone();
     }
  }

, getState... ... - :

  Immutable mu = new Immutable();
  mu.state[1] = 'o';

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