我有一个超类“telefoon”（英语：telephone）。这个超类有一个子类“contactgevens”（egnlish contact data/user information）。这个子类'contactgevnes'也是子类/子类的一个超类，但与我的问题无关。
在超级班“telefoon”（电话）。

public class Telefoon {

//Properties.
private String soort; //Enlgish = Type (Mobile or landline)
private String nummer; //English = Number (Just the number).

//Getters and Setters.
//Just normal getters and setters of all properties. not relevant to show here.    

//Constructors.
public Telefoon(String soort, String nummer) {
    this.nummer = nummer;
    this.soort = soort;
}

/**This constructor does nothing but when I don't have this one it gives and error in the child 
class??? */
public Telefoon() {
    this.nummer = "000000000";
    this.soort = "vast";
}

//Methods.
//Not relevant for question.

子类/子类“contactgevens”。

public class ContactGegevens extends Telefoon {

//Properties.
private String eMail;         //Email.
private Telefoon telefoon;    //Landline number.
private Telefoon gsm;         //Mobile phone number.

//Getters and Setters.
//Getters and Setters of all 3 properties. irrelevant to show here

//Constructors.
public ContactGegevens(String vast, String mobiel, String eMail) {
    /**
    *This works but in this case the 'extends Telefoon' is useless???!!
    As you can see I create 2 objects of superClass Telefoon. But then the 'extends Telefoon'
    is unnecessary, is there a Way i can do something like 

    telefoon = Super();
    gsm = Super(); 

    */
    telefoon = new Telefoon(vast,"vast");
    gsm = new Telefoon(mobiel, "mobiel");
    this.eMail = eMail;
}

//Methods.
public String toString() {
    return String.format("E-mail: %-15s %nTel: %-12s %nGSM: %-12s",eMail,telefoon.getNummer(), gsm.getNummer());
}

我的问题是类'contactgegevens'扩展了telefoon，但是在contactgegevens的构造函数中，我仍然需要创建两个类telefoon的对象，呈现'extends telefoon'无用。我能做一些像telefoon telefoon=super（//param here）；？
还有，为什么我需要在telefoon中使用一个默认构造函数，否则在“contactgevens”的构造函数中示例化对象“telefoon”时会出错。