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Depending on the required functionality, accessor methods may return a copy of the HashMap or a value contained by the HashMap. This compliant solution adds an accessor method that returns the value of an element given its key in the HashMap.  Make sure that you do not return references to private mutable objects from accessor methods (see OBJ05-J. Do not return references to private mutable class members for details).

Noncompliant Code Example (Public Final Array)

A nonzero-length array is always mutable. Declaring a public final array is a potential security risk as the array elements may be modified by a client. 

public final SomeType [] SOMETHINGS = { ... };

Compliant Solution (Copy the Array)

This compliant solution declares the array private and provides a public accessor method that returns a copy of the array:

private final SomeType [] SOMETHINGS = { ... };
public final SomeType [] somethings() {
  return SOMETHINGS.clone();
}

This approach prevents the elements of the class instance of the array from being modified by a client.

Compliant Solution (Construct an Immutable Object)

An alternative approach is to have a private array from which a public immutable list is contructed:

private final SomeType [] THE_THINGS = { ... };
public final List<SomeType> SOMETHINGS =
  Collections.unmodifiableList(Arrays.asList(THE_THINGS));

Neither the class instance field nor the public list can be modified by a client.

Exceptions

OBJ01-EX0: Fields with no associated behavior or invariants can be public.  According to Sun's Code Conventions document [Conventions 2009]:

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OBJ00-J. Limit the extensibility of classes and methods with invariants