如何使用流 Java 8 在 ListObjects 两个上迭代 List ObjectOne

Question

我有两个不同的列表，第一个是列表，第二个是列表 List studentList = new ArrayList(); List moduleList = new ArrayList();

如何在 studentList 上迭代 modulList，以便您可以看到哪个学生通过了哪个模块；

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班级学生{

private String studentId;
private String name;
private Type gender;
private String studClass;
private String education;
private HashMap<String, Module> faillOrPass;

public Student()
{
    faillOrPass = new HashMap<String, Module>();
}

public Student (String studentId, String name, Type gender, String studClass, String education)
{
    faillOrPass = new HashMap<String, Module>();
    setStudentId(studentId);
    setName(name);
    setGender(gender);
    setStudClass(studClass);
    setEducation(education);
}

public enum Type { MALE, FAML}

// getters and setters
// equals() and hashCode()
// toString()

}

类模块{

String modulecode;
int grade;
int year;

public Module(String code, int year) {
    setModule(code);
    setYear(year);
    setGrade(-1);
}

// getters and setters
// equals and hashCode
// toString

} 公共类 TestClass {

final static Student st = new Student();
static String ZAYNUL = st.setVolledigeNaam("Zaynul Zaini");
static String PIPO = st.setVolledigeNaam("Pipo");
static String SANNY = st.setVolledigeNaam("Sanny Saniwich");
static String JOHAN = st.setVolledigeNaam("Johan Ginger");
static String DURSAH = st.setVolledigeNaam("Dursah Pikobillo");
static String ROMAN = st.setVolledigeNaam("Roman Romanawich");
static String TOM = st.setVolledigeNaam("Johonson");
static String ANDRE = st.setVolledigeNaam("Andersons");

public static List<Vak> getModuleList() {
    return List.of(

            new Vak(ZAYNUL, "IT", 8, 2020),
            new Vak(SANNY, "IT", 10, 2019),
            new Vak(ROMAN, "IT", 9, 2018),
            new Vak(MALIKA, "IT", 8, 2017),
            new Vak(DURSAH,"IT", 10, 2016),
            new Vak(PIPO,"IT", 10, 2020),

            new Vak(PIPO,"IPC", 5, 2020),
            new Vak(ZAYNUL,"IPC", 6, 2019),
            new Vak(SANNY,"IPC", 4, 2018),
            new Vak(ROMAN,"IPC", 1, 2017),
            new Vak(MALIKA,"IPC", 5, 2016),
            new Vak(DURSAH,"IPC", 4, 2020));
}

public static List<Student> getStudentList() {
    List<Student> listVak = new ArrayList<>();
    listVak.add(new Student("011", ZAYNUL, Student.Type.MALE, "first year", "Architecture"));
    listVak.add(new Student("012", MALIKA, Student.Type.FEMALE, "second year", "economics"));
    listVak.add(new Student("013", SANNY, Student.Type.FEMALE, "third year", "IT"));
    listVak.add(new Student("014", ROMAN, Student.Type.MALE, "fourth year", "Astronomy"));
    listVak.add(new Student("015", TOM, Student.Type.MALE, "second year", "economics"));
    listVak.add(new Student("016", ANDRE, Student.Type.FEMALE, "third year", "IT"));
    listVak.add(new Student("017", JOHAN, Student.Type.MALE, "fourth year", "Astronomy"));
    return listVak;
}

public static void  getPassedAndFaillModule(List<Student> listSt, List<Module> listVak) {

    List<Student> filteredList = listSt.stream()
            .filter(student -> listVak.stream()
                    .filter(md -> md.getCijfer() > 5)
                    .anyMatch(mdo -> mdo.getStudentName() !=null
                            && student.getVolledigeNaam().equals(mdo.getStudentName())))
            .collect(Collectors.toList());
    filteredList.forEach(x -> System.out.println(x));

}

public static void main(String[] args) {
    System.out.println("Print the result: ");
    getPassedAndFaillModule(getStudentList(), getModuleList());
}

}

这是我得到但不好的结果。

打印结果： StudentImpl{studentnummer='011', volledigeNaam='Zaynul Zaini', type='MALE', klaas='first year', studierichting='Architecture', vakkenLijst={}}

StudentImpl{studentnummer='012', volledigeNaam='Malika Ginger', type='FEMALE', klaas='second year', studierichting='economics', vakkenLijst={}}

StudentImpl{studentnummer='013', volledigeNaam='Sanny Saniwich', type='FEMALE', klaas='third year', studierichting='IT', vakkenLijst={}}

StudentImpl{studentnummer='014', volledigeNaam='Roman Romanawich', type='MALE', klaas='第四年', studierichting='Astronomy', vakkenLijst={}}

Answer 1

这里的主要问题是代码的不完整部分无法表示minimal reproducible example，相关的类和部分丢失（例如，StudentImpl 和vakkenLijst、Vak）。

可能需要进行以下重构：

• 在Student 类中提供模块列表（可能代替冗余的failOrPass 映射）并将其包含在toString() 方法中：

class Student {
    private List<Module> modules;

    public List<Module> getModules() {
        return this.modules;
    }
    public void setModules(List<Module> list) {
        this.modules = list;
    }

    @Override
    public String toString() {
        return name + ": " + modules;
    }
}

• 从Vak 类的实例在Module 中实现类复制构造函数：

class Module {

    String module;
    int grade;
    int year;

    public Module(Vak vak) {
        this(vak.getModule(), vak.getGrade(), vak.getYear());
    }

    public Module(String code, int grade, int year) {
        setModule(code);
        setGrade(grade);
        setYear(year);
    }
// getters/setters/etc.

    @Override
    public String toString() {
        return String.format("Module: %s, grade=%d, year=%d", module, grade, year);
    }
}

• 重命名方法getPassedAndFaillModule - getter 不应该有void 返回类型：

public static void fillVakDataForStudents(List<Student> students, List<Vak> vaks) {
    students.forEach(s ->
        s.setModules(
            vaks.stream()
                //.filter(v.getGrade() > 5) // optionally filter by grade
                .filter(v -> v.getStudentName().equals(s.getName()))
                .map(Module::new) // using copy-like constructor
                .collect(Collectors.toList())
        )
    );
    students.forEach(System.out::println);
}

那么对于缩短的测试数据（没有Student的不必要细节）结果如下：

static String ZAYNUL = "Zaynul Zaini";
static String PIPO = "Pipo";
static String SANNY = "Sanny Saniwich";
static String JOHAN = "Johan Ginger";
static String DURSAH = "Dursah Pikobillo";
static String ROMAN = "Roman Romanawich";
static String TOM = "Johonson";
static String ANDRE = "Andersons";

public static List<Vak> getVakList() {
    return List.of(
        new Vak(ZAYNUL, "IT", 8, 2020),
        new Vak(SANNY, "IT", 10, 2019),
        new Vak(ROMAN, "IT", 9, 2018),
        new Vak(JOHAN, "IT", 8, 2017),
        new Vak(DURSAH,"IT", 10, 2016),
        new Vak(PIPO,"IT", 10, 2020),

        new Vak(PIPO,"IPC", 5, 2020),
        new Vak(ZAYNUL,"IPC", 6, 2019),
        new Vak(SANNY,"IPC", 4, 2018),
        new Vak(ROMAN,"IPC", 1, 2017),
        new Vak(JOHAN,"IPC", 5, 2016),
        new Vak(DURSAH,"IPC", 4, 2020)
    );
}

public static List<Student> getStudentList() {
    return List.of(
        new Student("011", ZAYNUL),
        new Student("012", PIPO),
        new Student("013", SANNY),
        new Student("014", ROMAN),
        new Student("015", TOM),
        new Student("016", ANDRE),
        new Student("017", JOHAN),
        new Student("018", DURSAH)
    );
}

// calling test method
fillVakDataForStudents(getStudentList(), getVakList());

输出：

Zaynul Zaini: [Module: IT, grade=8, year=2020, Module: IPC, grade=6, year=2019]
Pipo: [Module: IT, grade=10, year=2020, Module: IPC, grade=5, year=2020]
Sanny Saniwich: [Module: IT, grade=10, year=2019, Module: IPC, grade=4, year=2018]
Roman Romanawich: [Module: IT, grade=9, year=2018, Module: IPC, grade=1, year=2017]
Johonson: []
Andersons: []
Johan Ginger: [Module: IT, grade=8, year=2017, Module: IPC, grade=5, year=2016]
Dursah Pikobillo: [Module: IT, grade=10, year=2016, Module: IPC, grade=4, year=2020]