Lambda Expression - Predicate

原创转载请注明出处：http://agilestyle.iteye.com/blog/2424767

 

Predicate

Predicate是一个谓词函数，主要作为一个谓词演算推导真假值存在，返回布尔值。

 

e.g.

package org.fool.java8;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import java.util.function.BiPredicate;
import java.util.function.IntPredicate;
import java.util.function.Predicate;

public class PredicateTest {

    private static List<Person> filter(List<Person> persons, Predicate<Person> predicate) {
        List<Person> result = new ArrayList<>();

        for (Person person : persons) {
            if (predicate.test(person)) {
                result.add(person);
            }
        }

        return result;
    }

    private static List<Person> filterByAge(List<Person> persons, IntPredicate predicate) {
        List<Person> result = new ArrayList<>();

        for (Person person : persons) {
            if (predicate.test(person.getAge())) {
                result.add(person);
            }
        }

        return result;
    }

    private static List<Person> filterByNameAndAge(List<Person> persons, BiPredicate<String, Integer> predicate) {
        List<Person> result = new ArrayList<>();

        for (Person person : persons) {
            if (predicate.test(person.getName(), person.getAge())) {
                result.add(person);
            }
        }

        return result;
    }

    private static class Person {
        private String name;
        private Integer age;

        public Person(String name, Integer age) {
            this.name = name;
            this.age = age;
        }

        public String getName() {
            return name;
        }

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

        public Integer getAge() {
            return age;
        }

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

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

    public static void main(String[] args) {
        List<Person> list = Arrays.asList(
                new Person("zhangsan", 18),
                new Person("lisi", 28));

        filter(list, person -> person.getAge().equals(18)).forEach(System.out::println);

        filterByAge(list, age -> age > 18).forEach(System.out::println);

        filterByNameAndAge(list, (name, age) -> name.equals("zhangsan") && age < 28).forEach(System.out::println);
    }
}

Console Output

Person{name='zhangsan', age=18}
Person{name='lisi', age=28}
Person{name='zhangsan', age=18}