ImmutableRequiresFinalParameters

DRAFT

Correction

Here is what's right.

Whether or not local variables and constructor and method parameters are final has nothing to do with whether or not the class is immutable.

public class ImmutableCounter {

  private final int count;

  // parameter count is not final
  public ImmutableCounter(int count) {
    this.count = count;
  }

  public ImmutableCounter increment() {
    return new ImmutableCounter(count + 1);
  }
  
}

Origin

Where could this misconception come from?

This misconception may be related to the belief that immutability is equivalent to using final everywhere. It may reflect a superficial understanding of immutability, possibly originating in an instructors’ statement like “to make a class immutable, make everything final”, possibly combined with a confusion between shallow and deep immutability.