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

List 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 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

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