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how to reverse sort keys in a treemap?


TreeMap

TreeMap extends AbstractMap class and implements the NavigableMap interface. It contains the elements in key-value pair form. It maintains ascending order for its elements. It not allowed duplicate key.

Note: A TreeMap can have only one null key but can have multiple null values.

We can use descendingMap() method to reverse the map object in java.

Example

package com.codesjava;
 
import java.util.Map;
import java.util.TreeMap;
 
public class Test {
	public static void main(String args[]){
		//Create TreeMap object.
		TreeMap<Integer, String> treeMap = new TreeMap<Integer, String>();
 
		//Add objects to the TreeMap.
		treeMap.put(4, "Roxy");
		treeMap.put(2, "Sunil");
		treeMap.put(5, "Sandy");
		treeMap.put(1, "Munish");
		treeMap.put(3, "Pardeep");
 
		//Print the TreeMap object.
		System.out.println("TreeMap elements:");
		System.out.println(treeMap);
		//Reverse treemap elements
		Map<Integer, String> reverseTreeMap = treeMap.descendingMap();
		System.out.println("Reverse Map Content: ");
		System.out.println(reverseTreeMap);
	}
}

Output

TreeMap elements:
{1=Munish, 2=Sunil, 3=Pardeep, 4=Roxy, 5=Sandy}
Reverse Map Content: 
{5=Sandy, 4=Roxy, 3=Pardeep, 2=Sunil, 1=Munish}
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