java8 stream 处理list交集 差集 并集

package com.ccbckj.task;

import java.util.*;

import static java.util.stream.Collectors.toList;
public class Test {
    /**
     * 用于测试的对象类
     */
    static class Student {
        /**
         * 姓名
         */
        private String name;

        /**
         * 学号 唯一值
         */
        private String code;

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

        @Override
        public boolean equals(Object o) {
            if (this == o) {
                return true;
            }
            if (!(o instanceof Student)) {
                return false;
            }
            Student student = (Student) o;
            return code.equals(student.getCode());
        }

        @Override
        public int hashCode() {
            return Objects.hash(code);
        }

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

        public String getName() {
            return name;
        }

        public String getCode() {
            return code;
        }
    }

    /**
     * 对象类型的处理
     */
    public static void showObjectDeal() {
        List<Student> list1 = new ArrayList<>();
        list1.add(new Student("name1","1001"));
        list1.add(new Student("name2","1002"));
        list1.add(new Student("name3","1003"));

        List<Student> list2 = new ArrayList<>();
        list2.add(new Student("name3","1003"));
        list2.add(new Student("name4","1004"));

        Set<Student> list1Set = new HashSet<>(list1);

        Set<Student> list2Set = new HashSet<>(list2);

        // 交集
        List<Student> intersection = list1.stream().filter(list2Set::contains).collect(toList());
        System.out.println("---得到交集 intersection---");
        intersection.parallelStream().forEach(System.out::println);

        // 差集 (list1 - list2)
        List<Student> reduce1 = list1.stream().filter(item -> !list2Set.contains(item)).collect(toList());
        System.out.println("---得到差集 reduce1 (list1 - list2)---");
        reduce1.parallelStream().forEach(System.out::println);

        // 差集 (list2 - list1)
        List<Student> reduce2 = list2.stream().filter(item -> !list1Set.contains(item)).collect(toList());
        System.out.println("---得到差集 reduce2 (list2 - list1)---");
        reduce2.parallelStream().forEach(System.out::println);

        // 并集
        List<Student> listAll = list1.parallelStream().collect(toList());
        List<Student> listAll2 = list2.parallelStream().collect(toList());
        listAll.addAll(listAll2);
        System.out.println("---得到并集 listAll---");
        listAll.parallelStream().forEach(System.out::println);

        // 去重并集
        list1Set.addAll(list2Set);
        List<Student> listDistinctAll = new ArrayList<>(list1Set);
        System.out.println("---得到去重并集 listDistinctAll---");
        listDistinctAll.parallelStream().forEach(System.out::println);

        System.out.println("---原来的List1---");
        list1.parallelStream().forEach(System.out::println);
        System.out.println("---原来的List2---");
        list2.parallelStream().forEach(System.out::println);
    }

    /**
     * 简单类型的处理
     */
    public static void showSimpleDeal() {
        List<String> list1 = new ArrayList<>();
        list1.add("1111");
        list1.add("2222");
        list1.add("3333");

        List<String> list2 = new ArrayList<>();
        list2.add("3333");
        list2.add("4444");

        Set<String> list1Set = new HashSet<>(list1);

        Set<String> list2Set = new HashSet<>(list2);

        // 交集
        List<String> intersection = list1.stream().filter(list2Set::contains).collect(toList());
        System.out.println("---得到交集 intersection---");
        intersection.parallelStream().forEach(System.out::println);

        // 差集 (list1 - list2)
        List<String> reduce1 = list1.stream().filter(item -> !list2Set.contains(item)).collect(toList());
        System.out.println("---得到差集 reduce1 (list1 - list2)---");
        reduce1.parallelStream().forEach(System.out::println);

        // 差集 (list2 - list1)
        List<String> reduce2 = list2.stream().filter(item -> !list1Set.contains(item)).collect(toList());
        System.out.println("---得到差集 reduce2 (list2 - list1)---");
        reduce2.parallelStream().forEach(System.out::println);

        // 并集
        List<String> listAll = list1.parallelStream().collect(toList());
        List<String> listAll2 = list2.parallelStream().collect(toList());
        listAll.addAll(listAll2);
        System.out.println("---得到并集 listAll---");
        listAll.parallelStream().forEach(System.out::println);

        // 去重并集
        list1Set.addAll(list2Set);
        List<String> listDistinctAll = new ArrayList<>(list1Set);
        System.out.println("---得到去重并集 listDistinctAll---");
        listDistinctAll.parallelStream().forEach(System.out::println);

        System.out.println("---原来的List1---");
        list1.parallelStream().forEach(System.out::println);
        System.out.println("---原来的List2---");
        list2.parallelStream().forEach(System.out::println);
    }


    public static void main(String[] args) {
        // 基本类型测试
        showSimpleDeal();
        // 对象测试
        //showObjectDeal();

        // 一般有filter 操作时，不用并行流parallelStream ,如果用的话可能会导致线程安全问题 ！
        // parallelStream 由于是并行执行， 输出可能和list本身的顺序不一样 ！
    }
}