Add List to ArrayList

Issue

I am trying to add the Lists "studentList" and "handerwerkerList" to the new ArrayList plist. So i want my Objects to be all in one List. The other Lists have more parameters than the person objects. But i want to convert the other lists so they fit in the new list.

    static List <Person> personList = new ArrayList <Person>();
    static List <Student> studentList = new ArrayList <Student>();
    static List <Handwerker> handwerkerList = new ArrayList <Handwerker>();

    public static void main (String[] args) {

        PrintWriter out = new PrintWriter(System.out);

        testDifferentTypes(out);
        testRechnungen(out);
        out.flush();
    }
    public static void testDifferentTypes(PrintWriter out) {

        personList.add(new Person("Anton", "Kripp", 2001));
        studentList.add(new Student("Sarah", "Hirschfelder", 1993, "Wirschaftinformatik", 123456));
        studentList.add(new Student("Patrick", "Huf", 1990, "Informatik", 654321));
        studentList.add(new Student("AJ", "Kurpieweit", 1995, "Psychologie", 250702));
        handwerkerList.add(new Handwerker("Niko", "Budic", 2005, "Rohrleger", 9.82));

        ArrayList<Person> plist = new ArrayList <Person>();

        for(Person person  : personList) {
            plist.add(person);
        }

        for(Person person : studentList) {
            plist.add(person);
        }

        for (Person person : handwerkerList) {
            plist.add(person);
        }
    }

public class Student extends Person{

    protected String studienfach;
    protected int matrikelNr;

    public Student(String Vorname, String Nachname, int geburtsjahr, String studienfach, int matrikelNr) {
        super(Vorname, Nachname, geburtsjahr);
        this.studienfach = studienfach;
        this.matrikelNr = matrikelNr;
    }

    public Student(Person person, String studienfach, int matrikelNr) {
        this(person.Vorname, person.Nachname, person.geburtsjahr,studienfach, matrikelNr);
    }

public class Handwerker extends Person{

    protected String gewerk;
    protected Double stundenlohn;

    public Handwerker(String Vorname, String Nachname, int geburtsjahr, String gewerk, Double stundenlohn) {
        super(Vorname, Nachname, geburtsjahr);
        this.gewerk = gewerk;
        this.stundenlohn = stundenlohn;

    }
    public Handwerker(Person person, String gewerk, Double stundenlohn) {
        this(person.Vorname, person.Nachname, person.geburtsjahr, gewerk, stundenlohn);
    }

Solution

I recommend you spend some time reading about how inheritance works.

The answer to your question, if Student and Handweker already extend Person, then you can add them to any ArrayList<Person> directly.

Answered By - Yara