TreeMap in Java

In the previous post, we have learnt about LinkedHashMap. In this post, we will learn about TreeMap in java.

It has the following features as given below.

• It implements the NavigableMap interface and extends AbstractMap class.
• It contains only unique values.
• It can not have null key but can have multiple null values.
• It sorts the Map in ascending order.
• TreeMap is unsynchronized collection class which means it is not suitable for thread-safe operations until unless synchronized explicitly.

Let’s understand this with the Example.

import java.util.Iterator;
import java.util.Map;
import java.util.Map.Entry;
import java.util.TreeMap;

public class HashMapEx {

	public static void  main(String[] args){
		
		TreeMap<Integer,String> hm = new TreeMap<Integer,String>();
		hm.put(15, "Mobile");
		hm.put(6, "TV");
		hm.put(10, "Laptop");
		hm.put(2, "Desktop");
		hm.put(1, "Tablet");
		hm.put(23, "Microphone");
		
		Iterator iter = hm.entrySet().iterator();
		while(iter.hasNext()){
			Map.Entry m = (Entry) iter.next();
			//Maintains ascending order
			System.out.println(m.getKey()+"--"+m.getValue()); 
		}
		
	}
}

Output:

1–Tablet
2–Desktop
6–TV
10–Laptop
15–Mobile
23–Microphone