enums are generally thought of as constant, but an enum with a public field or public setter is non-constant. Ideally fields in an enum are private and set in the constructor, but if that’s not possible, their visibility should be reduced as much as possible.

Noncompliant Code Example

public enum Continent {

  NORTH_AMERICA (23, 24709000),
  // ...
  EUROPE (50, 39310000);

  public int countryCount;  // Noncompliant
  private int landMass;

  Continent(int countryCount, int landMass) {
    // ...
  }

  public void setLandMass(int landMass) {  // Noncompliant
    this.landMass = landMass;
  }

Compliant Solution

public enum Continent {

  NORTH_AMERICA (23, 24709000),
  // ...
  EUROPE (50, 39310000);

  private int countryCount;
  private int landMass;

  Continent(int countryCount, int landMass) {
    // ...
  }