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Java provides a convenient Collections.sort() method to sort a List of Object’s. The Objects in the list are required to implement the Comparable interface and the compareTo() method is used to compare Objects.

When an alternate sort order is needed you can do that using a Comparator which is passed to the sort() call.

The following example shows how you could sort a list of strings where the string contained a number (that should be sorted numerically) and a string (to be sorted alphabetically).

List<String> list = Arrays.asList(
   new String[] { "34 abc", "123 dfd", "34 xyz", "12 xxx" });

Collections.sort(list, new Comparator<String>() {

	@Override
	public int compare(String s1, String s2) {
		
		// separate the number and string
		
		String[] tokens1 = s1.split(" ");
		String[] tokens2 = s2.split(" ");
		
		// compare the number from each item
		
		int compare = Integer.parseInt(tokens1[0]) - Integer.parseInt(tokens2[0]);
		
		// If number same compare the string
		
		return compare==0 ? tokens1[1].compareTo(tokens2[1]) : compare;
	}
});

written by objects \\ tags: comparable, comparator, list, sort