java8特性快速对list集合的筛选过滤和计算

java8特性快速对list集合的筛选过滤和计算

一、准备工作
1.创建一个Student对象

package com.shiro.test.java8特性;

import java.io.Serializable;

/**
 * 学生的实体类
 */
public class Student implements Serializable {

    private String id;
    private String username;
    private Integer age;
    private String sex;
    private String status;

	//要加这个构造函数 为了给对象赋值
    public Student(String id, String username, int age, String sex,String status) {
        this.id = id;
        this.username = username;
        this.age = age;
        this.sex = sex;
        this.status = status;
    }
    public String getStatus() {
        return status;
    }
    public void setStatus(String status) {
        this.status = status;
    }
    public String getId() {
        return id;
    }
    public void setId(String id) {
        this.id = id;
    }
    public String getUsername() {
        return username;
    }
    public void setUsername(String username) {
        this.username = username;
    }

    public String getSex() {
        return sex;
    }
    public void setSex(String sex) {
        this.sex = sex;
    }
    public Integer getAge() {
        return age;
    }
    public void setAge(Integer age) {
        this.age = age;
    }
}

2.创建一个测试类，创建list集合，向list中添加数据

@Test
    public void test2(){
        List<Student> studentList = new ArrayList<>();
        Student s1 = new Student("1","小张",20,"男","0");
        Student s2 = new Student("2","小李",22,"男","1");
        Student s3 = new Student("3","小花",21,"女","1");
        Student s4 = new Student("4","小华",18,"女","2");
        Student s5 = new Student("5","小流",28,"男","2");
        Student s6 = new Student("6","小吴",25,"男","0");
        Student s7 = new Student("7","小吴",25,"男","0");
        Student s8 = new Student("8","小吴",25,"男","0");
        studentList.add(s1);
        studentList.add(s2);
        studentList.add(s3);
        studentList.add(s4);
        studentList.add(s5);
        studentList.add(s6);
        studentList.add(s7);
        studentList.add(s8);

二、利用java8特性Stream流对list集合进行操作
1.利用stream流进行foreach遍历

studentList.stream.forEach(student ->{
	//处理逻辑 打印出所有学生的名单和年龄
	 System.out.println(student.getUsername()+student.getAge());
	 
});

2.对studentList利用filter函数进行筛选 获取符合条件的

List<student> list = studentList.stream.filter(student ->Obgects.equals(studengt.getSex(),"女")).collect(Collectors.toList());
//list中存放的是性别是女的所有学生
//使用stream流进行foreach遍历
list.stream().forEach(student ->{
            System.out.println(student.getUsername()+student.getSex());
        });

3.对List集合进行去重

//将username相同的 进行去重
List<Student> unique = studentList.stream().collect(Collectors.collectingAndThen(
 Collectors.toCollection(() -> new TreeSet<>(Comparator.comparing(Student::getUsername))),ArrayList :: new));
unique.stream().forEach(student -> {
            System.out.println("-------------------"+student.getUsername());
        });

4.取出list集合对象中的某一个属性(取出list中的每一个对象的名字组成一个新的集合)

List<String> username=studentList.stream().map(Student::getUsername).collect(Collectors.toList());//不取重的

List<String> username = studentList.stream(),map(Student::getUsername).distinct().collect(Collectors.toList());//这个是将名字取重之后的

5.过滤属性为空的字段（添加一条数据 名字为空的数据） //获取名字不为空的

  Student s9 = new Student("9","",25,"男","0");
        studentList.add(s9);
        List<String> IsEmptyUsernameList= studentList.stream().map(s-> s.getUsername()).filter(s-> !s.isEmpty()).collect(Collectors.toList());
        System.out.println(IsEmptyUsernameList);

6.根据其中的某一属性值进行计算
//(获取年龄的最大值、最小值、平均值、综合、个数)

IntSummaryStatistics resultNum =  studentList.stream().mapToInt((s) -> s.getAge()).summaryStatistics();
        //个数
        System.out.println(resultNum.getCount());
        //总大小
        System.out.println(resultNum.getSum());
        //最大值
        System.out.println(resultNum.getMax());
        //最小值
        System.out.println(resultNum.getMin());
        //平均值
        System.out.println(resultNum.getAverage());

本文地址：https://blog.csdn.net/weixin_45170450/article/details/112859227