Discussion on java sorting and TreeSet sorting

TreeMap:

package com;

import java.util.Comparator;
import java.util.TreeMap;

public class Test5 {

	/**
	 * @param args
	 */
	public static void main(String[] args) {
		// TODO Auto-generated method stub
		TreeMap<String, String> tree = new TreeMap<String, String>(
				new Comparator<Object>() {
					@Override
					public int compare(Object o1, Object o2) {
						// TODO Auto-generated method stub
						if(o1 == null || o2 == null){
							return 0;
						}
						
						return o1.toString().compareTo(o2.toString());
					}
				}
		);
				
		
		tree.put("k", "1");
		tree.put("ba", "2");
		tree.put("z", "3");
		tree.put("d", "4");
		tree.put("e", "5");
		tree.put("an", "6");
		tree.put("c", "7");
		
		for(String str : tree.keySet()){
			System.out.println(str);
		}
	}
}

The default is KEY by default.

You can, however, write object comparators for custom sorting.

TreeSet: custom reverse sort, default sort in positive order, 1,2,3,4,5,6

package com;

import java.util.Comparator;
import java.util.TreeSet;

public class Test6 {

	/**
	 * @param args
	 */
	public static void main(String[] args) {
		// TODO Auto-generated method stub
		TreeSet<Object> tree = new TreeSet<Object>(new Comparator<Object>() {

			@Override
			public int compare(Object o1, Object o2) {
				// TODO Auto-generated method stub
				if(o1 == null || o2 == null){
					return 0;
				}
				
				if(Integer.parseInt(o1.toString()) > Integer.parseInt(o2.toString())){
					return -1;
				}else if(Integer.parseInt(o1.toString()) < Integer.parseInt(o2.toString())){
					return 1;
				}else{
					return 0;
				}
			}
		});
		
		tree.add(4);
		tree.add(5);
		tree.add(6);
		tree.add(1);
		tree.add(2);
		tree.add(3);

		for(Object o : tree){
			System.out.println(o);
		}
	}

}