链接列表中的Java自编程单链接列表

Question

At least for me, I have a tricky exercise to do for university. The task is to program a singly-linked-list with all kind of methods. So far so easy, but the challenge is to store these singly-linked-lists afterwards in a Linked-List. In the following you see my implementation of my singly-linked-list which actually runs smoothly:

public class Liste {

ListenElement first;
ListenElement last;
ListenElement current;
int count;

public Liste() {
    first = null;
    last = null;
    current = null;
    count = 0;
}

// Methods...

The single-linked list consists of list elements implemented in the following:

public class ListenElement {

String content;
ListenElement next;

public ListenElement(String content, ListenElement next)
{
    this.content = content;
    this.next = next;
}

//Methods...

Here is my problem:

LinkedList<Liste> zeilen = new LinkedList<>();
Liste zeile1 = new Liste();
Liste zeile2 = new Liste();

zeile1.addBehind("Hello");
zeile1.addBehind("World");
zeile2.addBehind("Hello");
zeile2.addBehind("World");

zeilen.add(zeile1);
zeilen.add(zeile2);

System.out.print(zeilen.get(1));
//Printed: Listen.Liste@4aa298b73 instead of Hello World.

Thank you in advance for your help!

Answer 1

 System.out.print(zeilen.get(1)); 

//Printed: Listen.Liste@4aa298b73 instead of Hello World.

That's the output of the default Object#toString . If you want different output from your Liste class, you need to override toString to provide that different output.

For example: If you wanted Liste#toString to return a comma-delimited list of the toString s of its contents:

@Override
public String toString() {
    StringBuffer sb = new StringBuffer(10 * this.count); // Complete guess
    ListenElement el = this.first;
    while (el != null) {
        sb.append(el.content.toString());
        el = el.next;
        if (el != null) {
            sb.append(", ");
        }
    }
    return sb.toString();
}

(I'm making assumptions there about how your list class works, based on the code you showed...)