Making Collections read only

Making a Collection Read-Only

Making a collection read-only involves wrapping the collection in another object whose mutation methods all throw UnsupportedOperationException.

List stuff = Arrays.asList(new String[]{"m", "d"});

// Make a list read-only

List list = new ArrayList(stuff);

list = Collections.unmodifiableList(list);

try {

// Try modifying the list

list.set(0, "value");

} catch (UnsupportedOperationException e) {

// Can't modify

}

// Make a set read-only

Set set = new HashSet(stuff);

set = Collections.unmodifiableSet(set);

// Make a map read-only

Map map = new HashMap();

// Add key/value pairs ...

map = Collections.unmodifiableMap(map);