Predicate.java revision 4b92e5b21380a5344e5808b17ddffb994f855288 
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25package java.util.function;
26
27import java.util.Objects;
28
29/**
30 * Represents a predicate (boolean-valued function) of one argument.
31 *
32 * <p>This is a <a href="package-summary.html">functional interface</a>
33 * whose functional method is {@link #test(Object)}.
34 *
35 * @param <T> the type of the input to the predicate
36 *
37 * @since 1.8
38 */
39@FunctionalInterface
40public interface Predicate<T> {
41
42    /**
43     * Evaluates this predicate on the given argument.
44     *
45     * @param t the input argument
46     * @return {@code true} if the input argument matches the predicate,
47     * otherwise {@code false}
48     */
49    boolean test(T t);
50
51    /**
52     * Returns a composed predicate that represents a short-circuiting logical
53     * AND of this predicate and another.  When evaluating the composed
54     * predicate, if this predicate is {@code false}, then the {@code other}
55     * predicate is not evaluated.
56     *
57     * <p>Any exceptions thrown during evaluation of either predicate are relayed
58     * to the caller; if evaluation of this predicate throws an exception, the
59     * {@code other} predicate will not be evaluated.
60     *
61     * @param other a predicate that will be logically-ANDed with this
62     *              predicate
63     * @return a composed predicate that represents the short-circuiting logical
64     * AND of this predicate and the {@code other} predicate
65     * @throws NullPointerException if other is null
66     */
67    default Predicate<T> and(Predicate<? super T> other) {
68        Objects.requireNonNull(other);
69        return (t) -> test(t) && other.test(t);
70    }
71
72    /**
73     * Returns a predicate that represents the logical negation of this
74     * predicate.
75     *
76     * @return a predicate that represents the logical negation of this
77     * predicate
78     */
79    default Predicate<T> negate() {
80        return (t) -> !test(t);
81    }
82
83    /**
84     * Returns a composed predicate that represents a short-circuiting logical
85     * OR of this predicate and another.  When evaluating the composed
86     * predicate, if this predicate is {@code true}, then the {@code other}
87     * predicate is not evaluated.
88     *
89     * <p>Any exceptions thrown during evaluation of either predicate are relayed
90     * to the caller; if evaluation of this predicate throws an exception, the
91     * {@code other} predicate will not be evaluated.
92     *
93     * @param other a predicate that will be logically-ORed with this
94     *              predicate
95     * @return a composed predicate that represents the short-circuiting logical
96     * OR of this predicate and the {@code other} predicate
97     * @throws NullPointerException if other is null
98     */
99    default Predicate<T> or(Predicate<? super T> other) {
100        Objects.requireNonNull(other);
101        return (t) -> test(t) || other.test(t);
102    }
103
104    /**
105     * Returns a predicate that tests if two arguments are equal according
106     * to {@link Objects#equals(Object, Object)}.
107     *
108     * @param <T> the type of arguments to the predicate
109     * @param targetRef the object reference with which to compare for equality,
110     *               which may be {@code null}
111     * @return a predicate that tests if two arguments are equal according
112     * to {@link Objects#equals(Object, Object)}
113     */
114    static <T> Predicate<T> isEqual(Object targetRef) {
115        return (null == targetRef)
116                ? Objects::isNull
117                : object -> targetRef.equals(object);
118    }
119}
120