java list 并集

使用apache的CollectionUtils工具类


String[] arrayA = new String[] { "1", "2", "3", "4"};
String[] arrayB = new String[] { "3", "4", "5", "6" };
List<String> listA = Arrays.asList(arrayA);
List<String> listB = Arrays.asList(arrayB);

//1、并集 union
System.out.println(CollectionUtils.union(listA, listB));
//输出: [1, 2, 3, 4, 5, 6]

对象集合交、并、差处理

import org.apache.commons.collections4.CollectionUtils;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
public class Person {
    private String name;
    private Integer age;
    public Person(String name, Integer age) {
        this.name = name;
        this.age = age;
    }
    /**
     * 为什么重写equals方法一定要重写hashCode方法下面也会讲
     */
    @Override
    public int hashCode() {
        String result = name + age;
        return result.hashCode();
    }
    /**
     * 重写 equals 方法 根据name和age都相同那么对象就默认相同
     */
    @Override
    public boolean equals(Object obj) {
        Person u = (Person) obj;
        return this.name.equals(u.name) && (this.age.equals(u.age));
    }
    /**
     * 重写 toString 方法
     */
    @Override
    public String toString() {
        return "Person{" +
                "name='" + name + '\'' +
                ", age=" + age +
                '}';
    }

    public static void main(String[] args) {
        List<Person> personList = new ArrayList<Person>();
        Person person1 = new Person("小小",3);
        Person person2 = new Person("中中",4);
        personList.add(person1);
        personList.add(person2);

        List<Person> person1List = new ArrayList<Person>();
        Person person3 = new Person("中中",4);
        Person person4 = new Person("大大",5);
        person1List.add(person3);
        person1List.add(person4);
        /**
         * 1、差集
         */
        System.out.println(CollectionUtils.subtract(personList, person1List));
        //输出:[Person{name='小小', age=3}]

        /**
         * 2、并集
         */
        System.out.println(CollectionUtils.union(personList, person1List));
        //输出:[Person{name='小小', age=3}, Person{name='中中', age=4}, Person{name='大大', age=5}]

        /**
         * 3、交集
         */
        System.out.println(CollectionUtils.intersection(personList, person1List));
        //输出:[Person{name='中中', age=4}]

        /**
         * 4、交集的补集（析取）
         */
        System.out.println(CollectionUtils.disjunction(personList, person1List));
        //输出:[Person{name='小小', age=3}, Person{name='大大', age=5}]
    }
}