How to sort a linked list with objects in java

Question

I've created a linked list (generic containers) with objects in Java. I need to re-write my insert-method to make the list sorted alphabetically by keys. This is my code so far:

Container:

class Sellbeholder<N extends Comparable<N>, V> implements INF1010samling<N,V> {

private Keeper første;
private int ant = 0;

private class Keeper {
    Keeper neste;
    N n;
    V v;

    Keeper(N n,V v) {
        this.n = n;
        this.v = v;
    }
}

This is my insert method (which I need to rewrite):

public void PutIn(N n, V v) {
    Keeper kep = new Keeper(n,v);
    kep.neste = første;
    første = kep;
    ant++;

This is the Person-object, which I'm putting in the container(linked list):

class Person {

    String name;

    Person(String n) {
        this.name = n;
    }
}

And this is how I create persons and put them in container:

Sellbeholder <String,Person> b1 = new Sellbeholder <String,Person>();
Person a = new Person("William");
b1.PutIn("William",a);

Any help would me much appreciated. I know I need to use the CompareTo-metohod to check where to put the object, but I'm not sure how the structure of the linked list should be set. I've started on this:

for(Keeper nn = første; nn!= null; nn = nn.neste) {

    if(nn.n.compareTo(kep.n) > 0) {
        //Do something here

Any reason why you can't use a TreeSet instead? docs.oracle.com/javase/6/docs/api/java/util/TreeSet.html — anoopelias
– anoopelias, Commented Feb 27, 2013 at 15:22
If you need a linked list you can use java.util.LinkedList and if you need a Map sorted by the key you can use java.util.TreeMap. I think TreeMap does what you are looking for. — Raphaël
– Raphaël, Commented Feb 27, 2013 at 15:29
@anoopelias Probably he has to implement it himself, e.g. like a homework. — gaborsch
– gaborsch, Commented Feb 27, 2013 at 15:31
I would recommend to use the Java conventions, start methods with lower case letters, and refrain from using national language characters. — gaborsch
– gaborsch, Commented Feb 27, 2013 at 15:42

gaborsch · Accepted Answer · 2013-02-27 15:39:48Z

1

Iterate on the list until you get the proper place:

public void PutIn(N n, V v) {
    Keeper kep = new Keeper(n,v);
    // you will insert between previous and current
    Keeper previous = null;
    Keeper current = første;

    // loop until you get the right place        
    while (current != null && ((current.n).compareTo(n) > 0)) {
        previous = current;
        current = current.neste;
    }

    // insert your stuff there (if there were no previous, then this is the first one)
    if (previous == null) {
        første = kep;
    } else {
        previous.neste = kep;
    }

    // Set the next Keeper
    kep.neste = current;

    ant++;
}

This will keep your list ordered.

answered Feb 27, 2013 at 15:39

gaborsch

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nkukhar · Accepted Answer · 2013-02-27 15:31:03Z

0

Try to use Collections.sort(List l) or Collections.sort(List l, Comparator c)

answered Feb 27, 2013 at 15:31

nkukhar

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