In Java 8 – How to sort a Map?
On Crunchify we have written almost ~400 java tutorials and this one is an addition to Java8 category.
I love Java collection and have multiple tutorials on How to iterate through Map and List, LinkedList, JSONArray and lot more.
In this tutorial we will go over Best way to sort HashMap by Key and Value in Java8.
Let’s get started:
- We will create class CrunchifySortMapByKeyValueJava8.java
- Create HashMap<String, Integer> crunchifyMap and that’s what we will use for sort by Key and Value.
For KEY: we are going to add random company from list- Patter: Random Number between 1 to 10 + (-) + 1 company from list
- companies list: crunchify.com, google.com, twitter.com
For VALUE: we are going to add one random number between 1 to 50- We will print original Map, Sorted by Key Map and Sorted by Value Map
Map.Entry.
comparingByKey()returns a comparator that compares Map.Entry in natural order on key.Map.Entry.
comparingByValue()returns a comparator that compares Map.Entry in natural order on value.
Here is a complete Java code:
Please take a look at two questions mentioned in below code carefully 
These are simple utilities just incase if you want to use it in your project.
CrunchifySortMapByKeyValueJava8.java
package crunchify.com.tutorial;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.LinkedHashMap;
import java.util.Map;
import java.util.Random;
import java.util.stream.Stream;
/**
* @author Crunchify.com
*
* Best way to sort HashMap by Key and Value in Java8 - Tutorial by App Shah
*
*/
public class CrunchifySortMapByKeyValueJava8 {
private static final Random crunchifyRandom = new Random();
public static void main(String[] argv) {
Map<String, Integer> crunchifyMap = new HashMap<>();
// Let's first create companies ArrayList
ArrayList<String> companies = new ArrayList<>();
companies.add("Crunchify.com");
companies.add("Google.com");
companies.add("Twitter.com");
// Let's add 10 entries to HashMap crunchifyMap
for (int i = 1; i <= 10; ++i) {
// How to get Random value from ArrayList?
String company = companies.get(crunchifyRandom.nextInt(companies.size()));
// Basically we are creating
// Key with pattern: 1-Crunchify, 5-Google, and so on...
// Random Value: Number between 1 to 50
crunchifyMap.put(crunchifyRandom.nextInt(10) + "-" + company, crunchifyRandom.nextInt(50));
}
crunchifyLog("~~~~~~~~~~~~~~Original HashMap (crunchifyMap value)~~~~~~~~~~~~~~");
crunchifyLog(crunchifyMap);
crunchifyLog("\n~~~~~~~~~~~~~~Updated HashMap after Sorting by Key~~~~~~~~~~~~~~");
// Map: An object that maps keys to values. A map cannot contain duplicate keys; each key can map to at most one value.
Map<String, Integer> key = crunchifySortByKey(crunchifyMap);
iterateThroughHashMapJava8(key);
crunchifyLog("\n~~~~~~~~~~~~~~Updated HashMap after Sorting by Value~~~~~~~~~~~~~~");
Map<String, Integer> value = crunchifySortByValue(crunchifyMap);
iterateThroughHashMapJava8(value);
}
// Simple Log Statement
private static void crunchifyLog(Object string) {
System.out.println(string);
}
// How to Iterate through HashMap in Java 8?
private static void iterateThroughHashMapJava8(Map<String, Integer> crunchifyMap) {
crunchifyMap.forEach((k, v) -> {
System.out.println("Key: " + k + "\t\t\t Value: " + v);
});
}
// Let's sort HashMap by Key
// Comparable: This interface imposes a total ordering on the objects of each class that implements it.
// This ordering is referred to as the class's natural ordering, and the class's compareTo method is referred to as its natural comparison method.
public static <K extends Comparable<? super K>, V> Map<K, V> crunchifySortByKey(Map<K, V> crunchifyMap) {
Map<K, V> crunchifyResult = new LinkedHashMap<>();
Stream<Map.Entry<K, V>> sequentialStream = crunchifyMap.entrySet().stream();
// comparingByKey() returns a comparator that compares Map.Entry in natural order on key.
sequentialStream.sorted(Map.Entry.comparingByKey()).forEachOrdered(c -> crunchifyResult.put(c.getKey(), c.getValue()));
return crunchifyResult;
}
// Let's sort HashMap by Value
public static <K, V extends Comparable<? super V>> Map<K, V> crunchifySortByValue(Map<K, V> crunchifyMap) {
Map<K, V> crunchifyResult = new LinkedHashMap<>();
// Stream: A sequence of elements supporting sequential and parallel aggregate operations.
// The following example illustrates an aggregate operation using Stream and IntStream.
Stream<Map.Entry<K, V>> sequentialStream = crunchifyMap.entrySet().stream();
// comparingByValue() returns a comparator that compares Map.Entry in natural order on value.
// sorted(): Returns a stream consisting of the elements of this stream, sorted according to the provided Comparator.
sequentialStream.sorted(Map.Entry.comparingByValue()).forEachOrdered(c -> crunchifyResult.put(c.getKey(), c.getValue()));
// getValue(): Returns the value corresponding to this entry. If the mapping has been removed from the backing map (by the iterator's remove operation), the results of this call are undefined.
// getKey(): Returns the key corresponding to this entry.
return crunchifyResult;
}
}
Eclipse Console Output:
Just run above program as a Java Application and you should see result like below.
~~~~~~~~~~~~~~Original HashMap (crunchifyMap value)~~~~~~~~~~~~~~
{9-Google.com=36, 6-Twitter.com=17, 3-Google.com=39, 2-Twitter.com=43, 5-Crunchify.com=2, 8-Google.com=5, 8-Crunchify.com=47, 5-Google.com=10, 7-Google.com=3}
~~~~~~~~~~~~~~Updated HashMap after Sorting by Key~~~~~~~~~~~~~~
Key: 2-Twitter.com Value: 43
Key: 3-Google.com Value: 39
Key: 5-Crunchify.com Value: 2
Key: 5-Google.com Value: 10
Key: 6-Twitter.com Value: 17
Key: 7-Google.com Value: 3
Key: 8-Crunchify.com Value: 47
Key: 8-Google.com Value: 5
Key: 9-Google.com Value: 36
~~~~~~~~~~~~~~Updated HashMap after Sorting by Value~~~~~~~~~~~~~~
Key: 5-Crunchify.com Value: 2
Key: 7-Google.com Value: 3
Key: 8-Google.com Value: 5
Key: 5-Google.com Value: 10
Key: 6-Twitter.com Value: 17
Key: 9-Google.com Value: 36
Key: 3-Google.com Value: 39
Key: 2-Twitter.com Value: 43
Key: 8-Crunchify.com Value: 47
Let us know if you face any issue running above program.
The post How to Sort a HashMap by Key and Value in Java 8 – Complete Tutorial appeared first on Crunchify.
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