In the final article, I receive got shown you lot how to sort a Map inwards Java 8 past times keys too today, I'll learn you lot how to sort a Map past times values using Java 8 features e.g. lambda expression, method reference, streams, too novel methods added into the java.util.Comparator too Map.Entry classes. In gild to sort whatever Map e.g. HashMap, Hashtable, LinkedHashMap, TreemMap, or fifty-fifty ConcurrentHashMap, you lot tin offset acquire laid upward of entries past times using the entrySet() method too hence you lot tin acquire the current past times calling the stream() method. The entrySet() method returns a Set which inherit the stream() method from the java.util.Collection class. Once you lot got the stream, you lot tin simply telephone telephone the sorted() method which tin sort all Map.Entry objects available inwards Stream using a Comparator.
In gild to compare entries of a Map past times values, you lot tin usage the newly added Map.Entry.comparingByValue() method from the java.util.Map.Entry class.
This is the counterpart of comparingByKey() method which nosotros receive got used inwards the last article. Both of these methods are overloaded to piece of occupation amongst both Comparable too Comparator objects.
Once you lot sort the stream, you lot tin create whatever you lot desire to create e.g. if you lot simply desire to impress keys, values, or entries inwards sorted order, simply usage the forEach() method or if you lot desire a Map which is sorted on values hence you lot tin usage the collect() method of current class.
This method accepts a Collector too allows you lot to capture all elements of Stream into whatever collection you lot desire to. For example, if you lot desire a sorted map hence you lot tin usage the toMap() method of java.util.stream.Collectors class.
This method is overloaded too provides a duad of choices, for example, you lot tin collect entries inwards whatever form of map or you lot tin too specify the form of map you lot desire similar for proceed entries inwards sorted order, we'll usage the LinkedHashMap. It too allows you lot to suspension ties inwards illustration of same values e.g. you lot tin adapt them inwards the gild you lot desire to.
Btw, If you lot are curious, you lot tin too encounter the Pluralsight's Map.entrySet() method.
2. Get the current of entries past times calling stream() method.
3. Call the sorted method amongst a Comparator.
5. Collect the lawsuit using the collect() method.
7. Provide LinkedHashMap::new to the final parameter to strength it to render a LinkedHashMap, to proceed the sorted gild preserved.
8. In gild to sort inwards decreasing order, simply opposite the gild of Comparator using Collections.reverseOrder() or Comparator.reverse() method of Java 8.
In gild to compare entries of a Map past times values, you lot tin usage the newly added Map.Entry.comparingByValue() method from the java.util.Map.Entry class.
This is the counterpart of comparingByKey() method which nosotros receive got used inwards the last article. Both of these methods are overloaded to piece of occupation amongst both Comparable too Comparator objects.
Once you lot sort the stream, you lot tin create whatever you lot desire to create e.g. if you lot simply desire to impress keys, values, or entries inwards sorted order, simply usage the forEach() method or if you lot desire a Map which is sorted on values hence you lot tin usage the collect() method of current class.
This method accepts a Collector too allows you lot to capture all elements of Stream into whatever collection you lot desire to. For example, if you lot desire a sorted map hence you lot tin usage the toMap() method of java.util.stream.Collectors class.
This method is overloaded too provides a duad of choices, for example, you lot tin collect entries inwards whatever form of map or you lot tin too specify the form of map you lot desire similar for proceed entries inwards sorted order, we'll usage the LinkedHashMap. It too allows you lot to suspension ties inwards illustration of same values e.g. you lot tin adapt them inwards the gild you lot desire to.
Btw, If you lot are curious, you lot tin too encounter the Pluralsight's Map.entrySet() method.
2. Get the current of entries past times calling stream() method.
3. Call the sorted method amongst a Comparator.
4. Use the Map.Entry.comparingByValue() comparator to sort entries past times values.
5. Collect the lawsuit using the collect() method.
6. Use Collectors.toMap() method to acquire the lawsuit inwards roughly other Map.
7. Provide LinkedHashMap::new to the final parameter to strength it to render a LinkedHashMap, to proceed the sorted gild preserved.
8. In gild to sort inwards decreasing order, simply opposite the gild of Comparator using Collections.reverseOrder() or Comparator.reverse() method of Java 8.
This is the novel method added into Comparator degree inwards Java SE 8. You tin farther see The Complete Java MasterClass for the total listing of novel methods added into fundamental Java classes e.g. Java Collection Framework, String, too Comparator, etc.
sec Once you lot follow this measurement you lot volition acquire a Map which is sorted past times values. Now that you lot know the theory too steps, let's encounter the code illustration inwards the adjacent department to acquire it right.
The Map fundamental is String, which represents detail too value is Integer, which is expenses. Our trace of piece of occupation is to sort the Map past times values to honour out which detail toll us most too impress all items inwards their decreasing gild of values.
You tin encounter that earlier sorting the map has a random gild inwards price of values but first, nosotros receive got sorted them inwards the increasing gild of values too afterward nosotros receive got sorted the same Map inwards the decreasing gild of values, that's why rent comes offset because it toll us highest.
2) Use method reference inwards house of lambda human face wherever you lot can. See this article to acquire to a greater extent than most how to convert lambda human face to method reference inwards Java 8, if you lot are non familiar amongst that.
That's all most how to sort a Map past times values inwards Java 8. You tin encounter that it's hence slow to sort the Map using novel methods added to existing classes. All that is possible because of the default method characteristic of JDK 8, which allows you lot to add together novel methods to existing classes.
Before this enhancement, it wasn't possible inwards Java without breaking the existing customer of interfaces because equally shortly equally you lot add together a novel method to an interface, all its clients had to implement it.
This is non required anymore if the method is default or static because they are non abstract but concrete methods.
Further Learning
The Complete Java MasterClass
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Thanks for reading this article hence far. If you lot similar this article hence delight part amongst your friends too colleagues. If you lot receive got whatever questions or suggestions hence delight drib a comment.
P.S.: If you lot simply desire to acquire to a greater extent than most novel features inwards Java 8 hence delight encounter the What's New inwards Java 8 online course of report on Pluralsight. It explains all the of import features of Java 8 similar lambda expressions, streams, functional interfaces, Optional, novel Date Time API too other miscellaneous changes.Java Program to sort a HashMap past times Values
Here is our consummate Java plan to sort a Map past times values using Java 8 features e.g. novel methods on existing classes inwards Java 8 past times evolving them using default methods too static methods on interfaces. In this example, I receive got got a Map of the map of items too their expenses similar rent, utility, transportation, etc.The Map fundamental is String, which represents detail too value is Integer, which is expenses. Our trace of piece of occupation is to sort the Map past times values to honour out which detail toll us most too impress all items inwards their decreasing gild of values.
import java.util.Collections; import java.util.Comparator; import java.util.HashMap; import java.util.LinkedHashMap; import java.util.Map; import static java.util.stream.Collectors.*; import static java.util.Map.Entry.*; /* * Java Program to sort a Map past times values inwards Java 8 * */ public class Main { public static void main(String[] args) throws Exception { // a Map amongst string keys too integer values Map<String, Integer> budget = new HashMap<>(); budget.put("clothes", 120); budget.put("grocery", 150); budget.put("transportation", 100); budget.put("utility", 130); budget.put("rent", 1150); budget.put("miscellneous", 90); System.out.println("map earlier sorting: " + budget); // let's sort this map past times values first Map<String, Integer> sorted = budget .entrySet() .stream() .sorted(comparingByValue()) .collect( toMap(e -> e.getKey(), e -> e.getValue(), (e1, e2) -> e2, LinkedHashMap::new)); System.out.println("map after sorting past times values: " + sorted); // inwards a higher house code tin live cleaned a fleck past times using method reference sorted = budget .entrySet() .stream() .sorted(comparingByValue()) .collect( toMap(Map.Entry::getKey, Map.Entry::getValue, (e1, e2) -> e2, LinkedHashMap::new)); // forthwith let's sort the map inwards decreasing gild of value sorted = budget .entrySet() .stream() .sorted(Collections.reverseOrder(Map.Entry.comparingByValue())) .collect( toMap(Map.Entry::getKey, Map.Entry::getValue, (e1, e2) -> e2, LinkedHashMap::new)); System.out.println("map after sorting past times values inwards descending order: " + sorted); } } Output map earlier sorting: {grocery=150, utility=130, miscellneous=90, rent=1150, clothes=120, transportation=100} map after sorting past times values: {miscellneous=90, transportation=100, clothes=120, utility=130, grocery=150, rent=1150} map after sorting past times values in descending order: {rent=1150, grocery=150, utility=130, clothes=120, transportation=100, miscellneous=90}
You tin encounter that earlier sorting the map has a random gild inwards price of values but first, nosotros receive got sorted them inwards the increasing gild of values too afterward nosotros receive got sorted the same Map inwards the decreasing gild of values, that's why rent comes offset because it toll us highest.
Some tips
1) Use static import to shorten the code, when you lot usage the static import characteristic to import both Map.Entry too java.util.stream.Collectors classes you lot tin refer their methods without including degree advert similar instead of Collectors.toMap() you lot tin simply usage toMap().2) Use method reference inwards house of lambda human face wherever you lot can. See this article to acquire to a greater extent than most how to convert lambda human face to method reference inwards Java 8, if you lot are non familiar amongst that.
That's all most how to sort a Map past times values inwards Java 8. You tin encounter that it's hence slow to sort the Map using novel methods added to existing classes. All that is possible because of the default method characteristic of JDK 8, which allows you lot to add together novel methods to existing classes.
Before this enhancement, it wasn't possible inwards Java without breaking the existing customer of interfaces because equally shortly equally you lot add together a novel method to an interface, all its clients had to implement it.
This is non required anymore if the method is default or static because they are non abstract but concrete methods.
Further Learning
The Complete Java MasterClass
books)
Thanks for reading this article hence far. If you lot similar this article hence delight part amongst your friends too colleagues. If you lot receive got whatever questions or suggestions hence delight drib a comment.