Predicate

源码：

@FunctionalInterface
public interface Predicate<T> {

    /**
     * Evaluates this predicate on the given argument.
     *
     * @param t the input argument
     * @return {@code true} if the input argument matches the predicate,
     * otherwise {@code false}
     */
    boolean test(T t);

    /**
     * Returns a composed predicate that represents a short-circuiting logical
     * AND of this predicate and another.  When evaluating the composed
     * predicate, if this predicate is {@code false}, then the {@code other}
     * predicate is not evaluated.
     *
     * <p>Any exceptions thrown during evaluation of either predicate are relayed
     * to the caller; if evaluation of this predicate throws an exception, the
     * {@code other} predicate will not be evaluated.
     *
     * @param other a predicate that will be logically-ANDed with this
     *              predicate
     * @return a composed predicate that represents the short-circuiting logical
     * AND of this predicate and the {@code other} predicate
     * @throws NullPointerException if other is null
     */
    default Predicate<T> and(Predicate<? super T> other) {
        Objects.requireNonNull(other);
        return (t) -> test(t) && other.test(t);
    }

    /**
     * Returns a predicate that represents the logical negation of this
     * predicate.
     *
     * @return a predicate that represents the logical negation of this
     * predicate
     */
    default Predicate<T> negate() {
        return (t) -> !test(t);
    }

    /**
     * Returns a composed predicate that represents a short-circuiting logical
     * OR of this predicate and another.  When evaluating the composed
     * predicate, if this predicate is {@code true}, then the {@code other}
     * predicate is not evaluated.
     *
     * <p>Any exceptions thrown during evaluation of either predicate are relayed
     * to the caller; if evaluation of this predicate throws an exception, the
     * {@code other} predicate will not be evaluated.
     *
     * @param other a predicate that will be logically-ORed with this
     *              predicate
     * @return a composed predicate that represents the short-circuiting logical
     * OR of this predicate and the {@code other} predicate
     * @throws NullPointerException if other is null
     */
    default Predicate<T> or(Predicate<? super T> other) {
        Objects.requireNonNull(other);
        return (t) -> test(t) || other.test(t);
    }

    /**
     * Returns a predicate that tests if two arguments are equal according
     * to {@link Objects#equals(Object, Object)}.
     *
     * @param <T> the type of arguments to the predicate
     * @param targetRef the object reference with which to compare for equality,
     *               which may be {@code null}
     * @return a predicate that tests if two arguments are equal according
     * to {@link Objects#equals(Object, Object)}
     */
    static <T> Predicate<T> isEqual(Object targetRef) {
        return (null == targetRef)
                ? Objects::isNull
                : object -> targetRef.equals(object);
    }
}

test(T t)

根据给定的判断方法，判断入参是否满足条件，返回true/false

public class PredicateTest {
    public static void main(String[] args) {
        //即：用e->e.length()>5 实现test(T t)方法
        Predicate<String> predicate=e->e.length()>5;
        System.out.println(predicate.test("shiyaochang")); //true
    }
}
public class PredicateTest {
    public static void main(String[] args) {
        List<Integer> list = Arrays.asList(1, 2, 3, 4, 5, 6, 7, 8, 9,10);
        list=filter(list, e -> e % 2 == 0); //过滤出偶数
        System.out.println(list);//[1, 3, 5, 7, 9]
    }

    private static List<Integer> filter(List<Integer> list, Predicate<Integer> predicate) {
        ArrayList<Integer> L = new ArrayList<>();
        for (Integer integer : list) {
            boolean B = predicate.test(integer);
            if (B) {
                L.add(integer);
            }
        }
        return L;
    }
}

and


//参数是一个Predicate，返回值也是一个Predicate，返回逻辑与，即对于入参T而言，要同时满足参数other的test和本身的test
//即： 用(t) -> test(t) && other.test(t)实现了返回的Predicate的test()方法
default Predicate<T> and(Predicate<? super T> other) {
        Objects.requireNonNull(other);
        return (t) -> test(t) && other.test(t);
    }

栗子：

public class PredicateTest2 {
    public static void main(String[] args) {
        //即：用e->e.length()>5 实现test(T t)方法
        Predicate<String> pre1 = e -> e.length() > 5;
        Predicate<String> pre2= e -> e.length() < 7;
        System.out.println(pre1.and(pre2).test("shiyaochang"));//false
        System.out.println(pre1.and(pre2).test("shiyao"));//true
    }

}

or

  //满足本事的test或者入参other的test其一即可
default Predicate<T> or(Predicate<? super T> other) {
        Objects.requireNonNull(other);
        return (t) -> test(t) || other.test(t);
    }

栗子：

public class PredicateTest2 {
    public static void main(String[] args) {
        //即：用e->e.length()>5 实现test(T t)方法
        Predicate<String> pre1 = e -> e.length() > 5;
        Predicate<String> pre2= e -> e.length() < 7;
        System.out.println(pre1.or(pre2).test("shiyaochang"));//true
        System.out.println(pre1.or(pre2).test("shiyao"));//true
    }

}

negate

返回相反值

栗子：

public class PredicateTest2 {
    public static void main(String[] args) {
        //即：用e->e.length()>5 实现test(T t)方法
        Predicate<String> pre1 = e -> e.length() > 5;
        System.out.println(pre1.negate().test("shiyaochang"));//false
        System.out.println(pre1.negate().test("sh"));//true
    }

}

isEqual

static <T> Predicate<T> isEqual(Object targetRef) {
       return (null == targetRef)
               ? Objects::isNull
               : object -> targetRef.equals(object);
    // 返回值是一个Predicate
    // 即用(null == targetRef)? Objects::isNull: object -> targetRef.equals(object)实现Predicate的test(),调用isEqual时判断targetRef是否为空，不为空则比较是否与test的入参object是否相等
   }

栗子：

public class PredicateTest2 {
    public static void main(String[] args) {
        PredicateTest2 T2=new PredicateTest2();
        System.out.println(T2.isEqualTest("shiyao").test("shiyao"));
        System.out.println(T2.isEqualTest("shiyao").test("shiyaochang"));
        System.out.println(T2.isEqualTest(null).test("shiyaochang"));

    }

    public Predicate<String> isEqualTest(Object str){
        return Predicate.isEqual(str);
        //Predicate.isEqual(str);会返回一个Predicate
        //如果str不为null,则会用表达式object -> targetRef.equals(object)实现该Predicate的test();
    }
}