Question

I’ve created an arraylist like this

ArrayList<String> entries = new ArrayList<String>();
entries.add("0 - name1");
entries.add("1000 - name2");
entries.add("1004 - name4");
entries.add("1002 - name3");
entries.add("10000 - name5");
entries.add("2000 - name5");

The list always starts with a number between 0 and 15,000 so when i sort i would like it to just sort based on the number none of the numbers will ever match and they should be assorted in an ascending order.

How can this be done with java can i use a comparator?

Answer 1

can i use a comparator?

yes, you can 🙂

with syntax : Collections.sort(entries,comparator); – you need to import java.util.Collections and write comparator that makes what you want. You may as well try .sort(entries) using default comparator (but here it will not work 🙂 ).

here’s complete solution:

import java.util.Comparator;

public class MyComparator implements Comparator<String> {

    @Override
    public int compare(String arg0, String arg1) {

        int indexOf = arg0.indexOf("-");
        String substring = arg0.substring(0, indexOf-1);
        int indexOf1 = arg1.indexOf("-");
        String substring1 = arg1.substring(0, indexOf1-1);
        return Integer.valueOf(substring) - Integer.valueOf(substring1);
    }

}


import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.List;

public class Runner {

    /**
     * @param args
     */
    public static void main(String[] args) {
        // TODO Auto-generated method stub
        List<String> entries = new ArrayList<String>();
        entries.add("0 - name1");
        entries.add("1000 - name2");
        entries.add("1004 - name4");
        entries.add("1002 - name3");
        entries.add("10000 - name5");
        entries.add("2000 - name5");

        Comparator<String> comparator = new MyComparator();
        Collections.sort(entries, comparator );

        for (String e : entries){
            System.out.println(e);
        }

    }
}

Also – I strongly suggest to declare lists likes this: List<String> entries = new ArrayList<String>(); Later you may find benefits of using LinkedList in place of ArrayList – then changing implementation of used list would be simplest possible.

Plz google “Program to interface not to implementation”. 🙂