Thread: how to sort arraylist of strings?

hi I have an Array List of <strings> holding phone numbers and index numbers separated by tab
example:

45 0876565645
14 0876476453
09 0876575657
111 0876575657
8211 0876575657

my question is how would I sort this list in order of first group of numbers while ignoring the phone numbers?
example:
09...
14...
45...
111...
8211...

any ideas would be great as all I can think of is a load of if statements but this list is 100+ long so that probably wont work

Implement a Comparator.

Originally Posted by PhHein

Implement a Comparator.

sorry i am a noob but i did look at the comparator class but how would it work without taking into account the phone numbers ?
i only want to sort them based on the index numbber

Split away the telephone number in the Comparator and just compare the indexes.

Originally Posted by PhHein

Split away the telephone number in the Comparator and just compare the indexes.

how ?? didint think that could be done without splitting the list into 2 lists and then joining them together which would just be a big mess is there an inbuilth function for this by the way this is code i am testing on

 ArrayList<String>a=new ArrayList<String>();
        a.add("123    2345462335:454");
        a.add("23    133445645335:454");
        a.add("1783    23456435:454");
        Collections.sort(a);
        for(String h:a){
            System.out.println(h);
        }

which ouptus

123    2345462335:454
1783    23456435:454
23    133445645335:454

thanks for help

No, you've got the string with the full number, and strings are immutable. So you extract the index into a new String and compare that to another extracted index.

so i am going to have create a bunch of lists and then join em back together DAMB!

NOOOO! You leave the list as is. Just extract the index in your compare method.

public int compare(String no1, String no2) {
		String index1 = getindex(no1);
		String index2 = getindex(no2);
		return index1.compareTo(index2);
	}
 
	private String getindex(String no1) {
		// TODO Auto-generated method stub
		return null;
	}