java8特性,java8新特性面试题

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","wxdqd",22,"男","1"); Student s3 = new Student("3","冷酷的大米",21,"女","1"); Student s4 = new Student("4","lldmt",18,"女","2"); Student s5 = new Student("5","小流",28,"男","2"); Student s6 = new Student("6","axdjm",25,"男","0"); Student s7 = new Student("7","axdjm",25,"男","0"); Student s8 = new Student("8","axdjm",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());