操作对象

package com.example.entity;import lombok.Data;@Data
public class Student {public Student(Integer id, String name, Integer age, String sex) {this.id = id;this.name = name;this.age = age;this.sex = sex;}// 学生idprivate Integer id;// 学生姓名private String name;// 学生年龄private Integer age;// 学生性别 0-女，1-男private String sex;}

模拟数据

public static void main(String[] args) {// 模拟数据Student s1 = new Student(100, "张三", 19, "1");Student s2 = new Student(101, "李四", 17, "1");Student s3 = new Student(102, "Lisa", 18, "0");Student s4 = new Student(103, "Jack", 19, "1");// 将模拟数据存入集合中List<Student> list = Arrays.asList(s1, s2, s3, s4);}

操作

1.过滤数据中年龄大于等于十八的学生

public static void main(String[] args) {// 模拟数据Student s1 = new Student(100, "张三", 19, "1");Student s2 = new Student(101, "李四", 17, "1");Student s3 = new Student(102, "Lisa", 18, "0");Student s4 = new Student(103, "Jack", 19, "1");// 将模拟数据存入集合中List<Student> list = Arrays.asList(s1, s2, s3, s4);// 筛选学生中年龄大于等于18的学生List<Student> collect = list.stream().filter(student -> student.getAge() >= 18).collect(Collectors.toList());// 打印新集合中的数据if (collect.size() > 0) {collect.forEach(System.out::println);}}

打印结果

2.获取对象中其中的一个字段并添加到集合(以学生姓名（name）为例)

public static void main(String[] args) {// 模拟数据Student s1 = new Student(100, "张三", 19, "1");Student s2 = new Student(101, "李四", 17, "1");Student s3 = new Student(102, "Lisa", 18, "0");Student s4 = new Student(103, "Jack", 19, "1");// 将模拟数据存入集合中List<Student> list = Arrays.asList(s1, s2, s3, s4);// 获取对象中其中的一个字段并添加到集合(以学生姓名（name）为例)List<String> collect = list.stream().map(Student::getName).collect(Collectors.toList());// 打印结果collect.forEach(System.out::println);}

打印结果

3.获取对象中其中的一个字段并转为其他数据类型最后添加到集合(以学生性别（sex）为例，将String转为Integer类型)

注意：异常自己捕捉，就比如这里String转Intger就可能出现NumberFormatException异常

public static void main(String[] args) {// 模拟数据Student s1 = new Student(100, "张三", 19, "1");Student s2 = new Student(101, "李四", 17, "1");Student s3 = new Student(102, "Lisa", 18, "0");Student s4 = new Student(103, "Jack", 19, "1");// 将模拟数据存入集合中List<Student> list = Arrays.asList(s1, s2, s3, s4);// 获取对象中其中的一个字段并转为其他数据类型最后添加到集合(以学生性别（sex）为例，将String转为Integer类型)List<Integer> collect = list.stream().map(Student::getSex).map(Integer::parseInt).collect(Collectors.toList());// 打印结果collect.forEach(System.out::println);}

打印结果

4.将对象中某个字段作为key，某个字段作为value（以id作为key，name作为value为例）

public static void main(String[] args) {// 模拟数据Student s1 = new Student(100, "张三", 19, "1");Student s2 = new Student(101, "李四", 17, "1");Student s3 = new Student(102, "Lisa", 18, "0");Student s4 = new Student(103, "Jack", 19, "1");// 将模拟数据存入集合中List<Student> list = Arrays.asList(s1, s2, s3, s4);// 取对象id为key，其他选一个字段为value（以学生姓名为例）Map<Integer, String> map = list.stream().collect(Collectors.toMap(Student::getId, Student::getName));System.out.println(map);}

打印结果

断点查看

5.将对象中某个字段作为key，某个字段作为value（以id作为key，学生对象作为value为例）

public static void main(String[] args) {// 模拟数据Student s1 = new Student(100, "张三", 19, "1");Student s2 = new Student(101, "李四", 17, "1");Student s3 = new Student(102, "Lisa", 18, "0");Student s4 = new Student(103, "Jack", 19, "1");// 将模拟数据存入集合中List<Student> list = Arrays.asList(s1, s2, s3, s4);// 取对象id为key，对象为value（以学生id为key，学生对象为value为例）Map<Integer, Student> map = list.stream().collect(Collectors.toMap(Student::getId, Function.identity()));System.out.println(map);}

打印结果

断点查看

持续更新中…