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25 package java.util.function;
26 
27 /**
28  * Represents an operation on a single operand that produces a result of the
29  * same type as its operand.  This is a specialization of {@code Function} for
30  * the case where the operand and result are of the same type.
31  *
32  * <p>This is a <a href="package-summary.html">functional interface</a>
33  * whose functional method is {@link #apply(Object)}.
34  *
35  * @param <T> the type of the operand and result of the operator
36  *
37  * @see Function
38  * @since 1.8
39  */
40 @FunctionalInterface
41 public interface UnaryOperator<T> extends Function<T, T> {
42 
43     /**
44      * Returns a unary operator that always returns its input argument.
45      *
46      * @param <T> the type of the input and output of the operator
47      * @return a unary operator that always returns its input argument
48      */
identity()49     static <T> UnaryOperator<T> identity() {
50         return t -> t;
51     }
52 }
53