# Replace static final Collections with Collections.unmodifiable...()
# Description
An unmodifiable Collection can be created with the matching Collections.unmodifiable...() method.
Some examples are Collections.unmodifiableList(), Collections.unmodifiableSortedSet(), etc.
A declaration of a Collection with the static and final modifiers is not sufficient because it might still be
modifiable.
The Collections which are created with Collections.unmodifiable...() throw an
UnsupportedOperationException as soon as a modification is attempted.
# Benefits
Applying this rule helps avoid common errors by making sure a static final field is always modifiable.
# Tags
# Code Changes
# Final Collection
Pre
private static final Collection<String> CONSTANT_COLLECTION = new ArrayList<String>() {
{
add("foo");
add("bar");
}
};
Post
private static final Collection<String> CONSTANT_COLLECTION = Collections.unmodifiableCollection(new ArrayList<String>() {
{
add("foo");
add("bar");
}
});
# Final Map
Pre
private static final Map<String, String> CONSTANT_MAP = new HashMap() {
{
put("foo", "bar");
}
};
Post
private static final Map<String, String> CONSTANT_MAP = Collections.unmodifiableMap(new HashMap() {
{
put("foo", "bar");
}
});
🛠️ Auto-refactor Available
You can auto-refactor this with jSparrow.
Drop this button to your Eclipse IDE workspace to install jSparrow for free:
Need help? Check out our installation guide.
# Properties
| Property | Value |
|---|---|
| Rule ID | ImmutableStaticFinalCollections |
| First seen in jSparrow version | 2.2.0 |
| Minimum Java version | 2 |
| Remediation cost | 10 min |
| Links |