Java Predicate

Predicate 接口说明

 /*
  * Copyright (c) 2010, 2013, Oracle and/or its affiliates. All rights reserved.
  * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
  */
 package java.util.function;

 import java.util.Objects;

 /**
  * Represents a predicate (boolean-valued function) of one argument.
  *
  * <p>This is a <a href="package-summary.html">functional interface</a>
  * whose functional method is {@link #test(Object)}.
  *
  * @param <T> the type of the input to the predicate
  *
  * @since 1.8
  */
 @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);
     }
 }

根据接口说明，Predicate 提供的为逻辑判断操作，即断言。

静态方法isEqual：判断是否相等，并返回一个Predicate对象

调用：Predicate.isEqual(Object1).test(Object2)

含义：使用Object1的equals方法判断Object2是否与其相等。

默认方法and，or，negate：分别代表逻辑判断与、或、非并都返回一个Predicate对象

调用：Predicate1.and(Predicate2).test(Object)

含义：判断Object对象是否满足Predicate1 && Predicate2

方法test：按照给定的Predicate条件进行逻辑判断。

 package org.htsg;

 import java.util.ArrayList;
 import java.util.List;
 import java.util.Objects;
 import java.util.function.Predicate;

 /**
  * @author HTSG
  */
 public class PredicateTest {
     public static void main(String[] args) {
         // 添加十个学生
         List<Student> studentList = new ArrayList<>(10);
         for (int i = 0; i < 10; i++) {
             studentList.add(new Student("student" + i, 10 + i));
         }
         // 获取年龄大于15的学生
         // [Student{name='student6', age=16}, Student{name='student7', age=17}, Student{name='student8', age=18}, Student{name='student9', age=19}]
         List<Student> filteredStudents = test(studentList, PredicateTest::filterAge1);
         System.out.println(filteredStudents);
         // 获取年龄大于15并且名字叫 "student7" 的学生
         // [Student{name='student7', age=17}]
         filteredStudents = and(studentList, PredicateTest::filterAge1, PredicateTest::filterName);
         System.out.println(filteredStudents);
         // 获取年龄不大于15的学生
         // [Student{name='student0', age=10}, Student{name='student1', age=11}, Student{name='student2', age=12}, Student{name='student3', age=13}, Student{name='student4', age=14}, Student{name='student5', age=15}]
         filteredStudents = negate(studentList, PredicateTest::filterAge1);
         System.out.println(filteredStudents);
         // 获取年龄不大于15或名字叫 "student7" 的学生
         // [Student{name='student0', age=10}, Student{name='student1', age=11}, Student{name='student2', age=12}, Student{name='student3', age=13}, Student{name='student4', age=14}, Student{name='student5', age=15}, Student{name='student7', age=17}]
         filteredStudents = or(studentList, PredicateTest::filterAge2, PredicateTest::filterName);
         System.out.println(filteredStudents);
         // 获取和目标学生属性值相同的学生列表
         // [Student{name='student1', age=11}]
         filteredStudents = isEqual(studentList, new Student("student1", 11));
         System.out.println(filteredStudents);

     }

     public static boolean filterAge1(Student student) {
         return student.getAge() > 15;
     }

     public static boolean filterAge2(Student student) {
         return student.getAge() <= 15;
     }

     public static boolean filterName(Student student) {
         return "student7".equals(student.getName());
     }

     public static List<Student> test(List<Student> students, Predicate<Student> pre) {
         List<Student> result = new ArrayList<>(10);
         for (Student student : students) {
             if (pre.test(student)) {
                 result.add(student);
             }
         }
         return result;
     }

     public static List<Student> and(List<Student> students, Predicate<Student> pre1, Predicate<Student> pre2) {
         List<Student> result = new ArrayList<>(10);
         for (Student student : students) {
             if (pre1.and(pre2).test(student)) {
                 result.add(student);
             }
         }
         return result;
     }

     public static List<Student> negate(List<Student> students, Predicate<Student> pre) {
         List<Student> result = new ArrayList<>(10);
         for (Student student : students) {
             if (pre.negate().test(student)) {
                 result.add(student);
             }
         }
         return result;
     }

     public static List<Student> or(List<Student> students, Predicate<Student> pre1, Predicate<Student> pre2) {
         List<Student> result = new ArrayList<>(10);
         for (Student student : students) {
             if (pre1.or(pre2).test(student)) {
                 result.add(student);
             }
         }
         return result;
     }

     public static List<Student> isEqual(List<Student> students, Student student) {
         List<Student> result = new ArrayList<>(10);
         for (Student studentTemp : students) {
             if (Predicate.isEqual(student).test(studentTemp)) {
                 result.add(studentTemp);
             }
         }
         return result;
     }

     // 创建静态内部类
     public static class Student {
         private String name;
         private int age;

         public Student() {
         }

         public Student(String name, int age) {
             this.name = name;
             this.age = age;
         }

         public String getName() {
             return name;
         }

         public void setName(String name) {
             this.name = name;
         }

         public int getAge() {
             return age;
         }

         public void setAge(int age) {
             this.age = age;
         }

         @Override
         public String toString() {
             return "Student{" +
                     "name='" + name + '\'' +
                     ", age=" + age +
                     '}';
         }

         @Override
         public boolean equals(Object o) {
             if (this == o) {
                 return true;
             }
             if (o == null || getClass() != o.getClass()) {
                 return false;
             }
             Student student = (Student) o;
             return age == student.age &&
                     Objects.equals(name, student.name);
         }
     }
 }