Java 8 Stream filter流式过滤器详解

// 定义 Student 类
public class Student {
    // 私有成员变量
    private int id;
    private String name;
    private String gender;
    private int age;
    // 构造函数，用于初始化 Student 对象
    public Student(int id, String name, String gender, int age) {
        super();
        this.id = id;
        this.name = name;
        this.gender = gender;
        this.age = age;
    }
    // 获取 id
    public int getId() {
        return id;
    }
    // 设置 id
    public void setId(int id) {
        this.id = id;
    }
    // 获取 name
    public String getName() {
        return name;
    }
    // 设置 name
    public void setName(String name) {
        this.name = name;
    }
    // 获取 gender
    public String getGender() {
        return gender;
    }
    // 设置 gender
    public void setGender(String gender) {
        this.gender = gender;
    }
    // 获取 age
    public int getAge() {
        return age;
    }
    // 设置 age
    public void setAge(int age) {
        this.age = age;
    }
    // 重写 toString 方法，用于打印对象信息
    @Override
    public String toString() {
        return "Student [id=" + id + ", name=" + name + ", gender=" + gender + ", age=" + age + "]";
    }
}

// 过滤所有男性学生
List maleStudents = studentList.stream()
    // 使用 filter 方法筛选性别为 "M" 的学生
    .filter(s -> s.getGender().equalsIgnoreCase("M"))
    // 使用 collect 将结果收集到新的列表中
    .collect(Collectors.toList());
System.out.println("Male students are :" + maleStudents);

// 根据名字进行过滤
Student student = studentList.stream()
    // 使用 filter 方法筛选名字为 "John" 的学生
    .filter(s -> s.getName().equalsIgnoreCase("John"))
    // 使用 findAny 找到任意一个匹配的学生
    .findAny()
    // 如果未找到匹配的学生，则返回 null
    .orElse(null);
System.out.println("Student with Name john :" + student);

import java.util.ArrayList;
import java.util.List;
import java.util.stream.Collectors;
public class Java8StreamFilterExamples {
    public static void main(String[] args) {
        // 创建学生列表
        List studentList = createStudentList();
        // 过滤所有男性学生
        List maleStudents = studentList.stream()
            .filter(s -> s.getGender().equalsIgnoreCase("M"))
            .collect(Collectors.toList());
        System.out.println("Male students are :" + maleStudents);
        // 根据名字进行过滤
        Student student = studentList.stream()
            .filter(s -> s.getName().equalsIgnoreCase("John"))
            .findAny()
            .orElse(null);
        System.out.println("Student with Name john :" + student);
    }
    // 创建并返回学生列表
    public static List createStudentList() {
        List studentList = new ArrayList();
        Student s1 = new Student(1, "Arpit", "M", 19);
        Student s2 = new Student(2, "John", "M", 17);
        Student s3 = new Student(3, "Mary", "F", 14);
        Student s4 = new Student(4, "Martin", "M", 21);
        Student s5 = new Student(5, "Monica", "F", 16);
        Student s6 = new Student(6, "Ally", "F", 20);
        // 将学生对象添加到列表中
        studentList.add(s1);
        studentList.add(s2);
        studentList.add(s3);
        studentList.add(s4);
        studentList.add(s5);
        studentList.add(s6);
        return studentList;
    }
}