$show=/label

How To Iterate TreeMap in older Java and new Java 8? Or How to iterate over each entry in a Java Map?

SHARE:

A quick guide on how to iterate TreeMap in java in different ways with example programs and explore the different scenarios.

1. Overview

In this tutorial, We will learn how to iterate the map in older java versions and examples in java 8.

And alos let us explore how to iterate the keys of TreeMap sorted that means in the ascending order.

TreeMap can be used where we want the map sorted based on the key by default in the ascending or descending order use cases.

java 8 TreeMap Iterate Examples


2. Example to Iterate the TreeMap before JDK 8


In the below code we have created the TreeMap object and added few key value pairs. Here key is the type String and Value is type of Integer.


package com.javaprogramto.collections.treemap;

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

public class TreeMapIterate {

	public static void main(String[] args) {
		
		// Creating the TreeMap object
		Map<String, Integer> studentsCountMap = new TreeMap<>();
		
		// Adding students class and no of students in the class
		studentsCountMap.put("2nd class", 200);
		studentsCountMap.put("1nd class", 100);
		studentsCountMap.put("4nd class", 400);
		studentsCountMap.put("5nd class", 500);
		studentsCountMap.put("3nd class", 300);
		
		// Getting the Set object using keySet() method
		Set<String> keysSet = studentsCountMap.keySet();
		
		// Getting the iterator object
		Iterator<String > it = keysSet.iterator();
		
		// Iterating the map using regular method of iterator.
		while (it.hasNext()) {
			String key = it.next();
			System.out.println("Key - "+key+", Value - "+studentsCountMap.get(key));
		}

	}

}

Output:

Key - 1nd class, Value - 100
Key - 2nd class, Value - 200
Key - 3nd class, Value - 300
Key - 4nd class, Value - 400
Key - 5nd class, Value - 500

In the above program, we have first got the all the keys of treemap using keySet() method and next used the iterator() method to get the Iterator instance.

Finally, used the traditional iterate method workflow to get the each key from iterator and passed the key to treemap to get the value of the corresponding key.

3. Java 8 Lamdba Foreach TreeMap


Next, Look at the below program to get the keys and values of TreeMap using Java 8 Lambda expressions with forEach() method.

package com.javaprogramto.collections.treemap;

import java.util.Map;
import java.util.TreeMap;

public class TreeMapIterateJava8 {

	public static void main(String[] args) {

		// Creating the TreeMap object
		Map<String, Integer> studentsCountMap = new TreeMap<>();

		// Adding students class and no of students in the class
		studentsCountMap.put("2nd class", 200);
		studentsCountMap.put("1nd class", 100);
		studentsCountMap.put("4nd class", 400);
		studentsCountMap.put("5nd class", 500);
		studentsCountMap.put("3nd class", 300);

		// Java 8 lambda foreach
		studentsCountMap.forEach((key, value) -> {
			System.out.println("Key - " + key + ", Value - " + value);
		});
	}
}

This ways also produces the same output as seen in the above section. This is the simplified version in java 8 and it internally uses the BiConsumer functional interface.


4. Java 8 Stream Foreach TreeMap EntrySet


Finally, explore the java 8 stream construct to get the Entry object from stream and pass it to forEach method.

package com.javaprogramto.collections.treemap;

import java.util.Map;
import java.util.TreeMap;

public class TreeMapIterateJava8 {

	public static void main(String[] args) {

		// Creating the TreeMap object
		Map<String, Integer> studentsCountMap = new TreeMap<>();

		// Adding students class and no of students in the class
		studentsCountMap.put("2nd class", 200);
		studentsCountMap.put("1nd class", 100);
		studentsCountMap.put("4nd class", 400);
		studentsCountMap.put("5nd class", 500);
		studentsCountMap.put("3nd class", 300);

		// java 8 Stream entry forEach
		studentsCountMap.entrySet().stream().forEach(
				entry -> System.out.println("entry key - " + entry.getKey() + ", entry value - " + entry.getValue()));
	}
}


Output:
entry key - 1nd class, entry value - 100
entry key - 2nd class, entry value - 200
entry key - 3nd class, entry value - 300
entry key - 4nd class, entry value - 400
entry key - 5nd class, entry value - 500

5. Conclusion


In this article, We have seen how to iterate the TreeMap in older and new JDK versions with examples.





COMMENTS

BLOGGER

About Us

Author: Venkatesh - I love to learn and share the technical stuff.
Name

accumulo,1,ActiveMQ,2,Adsense,1,API,37,ArrayList,18,Arrays,24,Bean Creation,3,Bean Scopes,1,BiConsumer,1,Blogger Tips,1,Books,1,C Programming,1,Collection,8,Collections,37,Collector,1,Command Line,1,Comparator,1,Compile Errors,1,Configurations,7,Constants,1,Control Statements,8,Conversions,6,Core Java,149,Corona India,1,Create,2,CSS,1,Date,3,Date Time API,38,Dictionary,1,Difference,2,Download,1,Eclipse,3,Efficiently,1,Error,1,Errors,1,Exceptions,8,Fast,1,Files,17,Float,1,Font,1,Form,1,Freshers,1,Function,3,Functional Interface,2,Garbage Collector,1,Generics,4,Git,9,Grant,1,Grep,1,HashMap,2,HomeBrew,2,HTML,2,HttpClient,2,Immutable,1,Installation,1,Interview Questions,6,Iterate,2,Jackson API,3,Java,32,Java 10,1,Java 11,6,Java 12,5,Java 13,2,Java 14,2,Java 8,128,Java 8 Difference,2,Java 8 Stream Conversions,4,java 8 Stream Examples,12,Java 9,1,Java Conversions,14,Java Design Patterns,1,Java Files,1,Java Program,3,Java Programs,114,Java Spark,1,java.lang,4,java.util. function,1,JavaScript,1,jQuery,1,Kotlin,11,Kotlin Conversions,6,Kotlin Programs,10,Lambda,2,lang,29,Leap Year,1,live updates,1,LocalDate,1,Logging,1,Mac OS,3,Math,1,Matrix,6,Maven,1,Method References,1,Mockito,1,MongoDB,3,New Features,1,Operations,1,Optional,6,Oracle,5,Oracle 18C,1,Partition,1,Patterns,1,Programs,1,Property,1,Python,2,Quarkus,1,Read,1,Real Time,1,Recursion,2,Remove,2,Rest API,1,Schedules,1,Serialization,1,Servlet,2,Sort,1,Sorting Techniques,8,Spring,2,Spring Boot,23,Spring Email,1,Spring MVC,1,Streams,31,String,61,String Programs,28,String Revese,1,StringBuilder,1,Swing,1,System,1,Tags,1,Threads,11,Tomcat,1,Tomcat 8,1,Troubleshoot,26,Unix,3,Updates,3,util,5,While Loop,1,
ltr
item
JavaProgramTo.com: How To Iterate TreeMap in older Java and new Java 8? Or How to iterate over each entry in a Java Map?
How To Iterate TreeMap in older Java and new Java 8? Or How to iterate over each entry in a Java Map?
A quick guide on how to iterate TreeMap in java in different ways with example programs and explore the different scenarios.
https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEivgEVvUpF2Zi3l073etdPEpTZx76K6Xro2M4r736vrVVlnQpIz7Up7woeqFXIMrlNMJ64-Gt5XyPnOiErAwlzQJhbyhFKgVGULJTEJDHAf6r5xcMo2YObOGuTyl2_E641iWzeRLeS97Qw/w400-h289/java+8+TreeMap+Iterate+Examples.png
https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEivgEVvUpF2Zi3l073etdPEpTZx76K6Xro2M4r736vrVVlnQpIz7Up7woeqFXIMrlNMJ64-Gt5XyPnOiErAwlzQJhbyhFKgVGULJTEJDHAf6r5xcMo2YObOGuTyl2_E641iWzeRLeS97Qw/s72-w400-c-h289/java+8+TreeMap+Iterate+Examples.png
JavaProgramTo.com
https://www.javaprogramto.com/2021/01/java-iterate-treemap.html
https://www.javaprogramto.com/
https://www.javaprogramto.com/
https://www.javaprogramto.com/2021/01/java-iterate-treemap.html
true
3124782013468838591
UTF-8
Loaded All Posts Not found any posts VIEW ALL Readmore Reply Cancel reply Delete By Home PAGES POSTS View All RECOMMENDED FOR YOU LABEL ARCHIVE SEARCH ALL POSTS Not found any post match with your request Back Home Sunday Monday Tuesday Wednesday Thursday Friday Saturday Sun Mon Tue Wed Thu Fri Sat January February March April May June July August September October November December Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec just now 1 minute ago $$1$$ minutes ago 1 hour ago $$1$$ hours ago Yesterday $$1$$ days ago $$1$$ weeks ago more than 5 weeks ago Followers Follow THIS PREMIUM CONTENT IS LOCKED STEP 1: Share to a social network STEP 2: Click the link on your social network Copy All Code Select All Code All codes were copied to your clipboard Can not copy the codes / texts, please press [CTRL]+[C] (or CMD+C with Mac) to copy Table of Content