Java8 使用 stream().filter()過濾List對象（查找符合條件的對象集合）

內容簡介

本文主要說明在Java8及以上版本中，使用stream().filter()來過濾一個List對象，查找符合條件的對象集合。

List對象類（StudentInfo）

public class StudentInfo implements Comparable<StudentInfo> {

    //名稱
    private String name;

    //性別 true男 false女
    private Boolean gender;

    //年齡
    private Integer age;

    //身高
    private Double height;

    //出生日期
    private LocalDate birthday;

    public StudentInfo(String name, Boolean gender, Integer age, Double height, LocalDate birthday){
        this.name = name;
        this.gender = gender;
        this.age = age;
        this.height = height;
        this.birthday = birthday;
    }

    public String toString(){
        String info = String.format("%s\t\t%s\t\t%s\t\t\t%s\t\t%s",this.name,this.gender.toString(),this.age.toString(),this.height.toString(),birthday.toString());
        return info;
    }

    public static void printStudents(List<StudentInfo> studentInfos){
        System.out.println("[姓名]\t\t[性別]\t\t[年齡]\t\t[身高]\t\t[生日]");
        System.out.println("----------------------------------------------------------");
        studentInfos.forEach(s->System.out.println(s.toString()));
        System.out.println(" ");
    }

    @Override
    public int compareTo(StudentInfo ob) {
        return this.age.compareTo(ob.getAge());
        //return 1;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public Boolean getGender() {
        return gender;
    }

    public void setGender(Boolean gender) {
        this.gender = gender;
    }

    public Integer getAge() {
        return age;
    }

    public void setAge(Integer age) {
        this.age = age;
    }

    public Double getHeight() {
        return height;
    }

    public void setHeight(Double height) {
        this.height = height;
    }

    public LocalDate getBirthday() {
        return birthday;
    }

    public void setBirthday(LocalDate birthday) {
        this.birthday = birthday;
    }
}

StudentInfo對象類

測試數據

//測試數據，請不要糾結數據的嚴謹性
List<StudentInfo> studentList = new ArrayList<>();
studentList.add(new StudentInfo("李小明",true,18,1.76,LocalDate.of(2001,3,23)));
studentList.add(new StudentInfo("張小麗",false,18,1.61,LocalDate.of(2001,6,3)));
studentList.add(new StudentInfo("王大朋",true,19,1.82,LocalDate.of(2000,3,11)));
studentList.add(new StudentInfo("陳小跑",false,17,1.67,LocalDate.of(2002,10,18)));

輸出Students列表

 //輸出List
StudentInfo.printStudents(studentList);

輸出結果以下圖：

 使用filter()過濾List

//查找身高在1.8米及以上的男生
List<StudentInfo> boys = studentList.stream().filter(s->s.getGender() && s.getHeight() >= 1.8).collect(Collectors.toList());
//輸出查找結果
StudentInfo.printStudents(boys);

結果以下圖：