@Target(value=TYPE)
@Retention(value=SOURCE)
public @interface ExtensionMethod

Extension methods enable you to "add" methods to existing types without creating a new derived type, recompiling, or otherwise modifying the original type. Extension methods are a special kind of static method, but they are called as if they were instance methods on the extended type.

Complete documentation is found at the project lombok features page for @ExtensionMethod.

Before:

 @ExtensionMethod(java.util.Arrays.class)
 class Example {
        private void example() {
                long[] values = new long[] { 2, 5, 7, 9 };
                values.copyOf(3).sort();
        }
 }
 

After:

 class Example {
        private void example() {
                long[] values = new long[] { 2, 5, 7, 9 };
                java.util.Arrays.sort(java.util.Arrays.copyOf(values, 3));
        }
 }