In this article, we will discuss how to convert ordered LinkedHashMap into Sorted TreeMap by its Values
With the introduction of Java 8 APIs, sorting LinkedHashMap become easy and more elegant, read below articles
- Java 8 – How to sort LinkedHashMap entries by its Key ?
- Java 8 – How to sort LinkedHashMap entries by its Value ?
1. Sorting LinkedHashMap in ascending order of values :
1.1 Ascending-order sorting steps :-
- get entrySet() from Map
- create/convert entry set into List of entries
- sort converted List using Collections class’ sort(); method by implementing Comparator for natural-ordering by its Values
- clear original LinkedHashMap using clear(); method
- Iterate List and add entries to original LinkedHashMap, after clearing
- finally print Map.Entry in console
1.2 Sorting LinkedHashMap by its values in ascending-order :
- LinkedHashMap maintains insertion-order of keys
- In below illustration, we will sort/convert LinkedHashMap into natural-ordering of values i.e.; ascending-order of values
SortingLinkedHashMapInAscOrderByValues.java
package in.bench.resources.collection;
import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.LinkedHashMap;
import java.util.List;
import java.util.Map;
import java.util.Map.Entry;
import java.util.Set;
public class SortingLinkedHashMapInAscOrderByValues {
public static void main(String[] args) {
// create LinkedHashMap object of type <String, String>
Map<String, String> linkMap =
new LinkedHashMap<String, String>();
// adding key-value pairs to LinkedHashMap object
linkMap.put("Google", "Sundar Pichai");
linkMap.put("Facebook", "Mark Zuckerberg");
linkMap.put("LinkedIn", "Reid Hoffman");
linkMap.put("Apple Inc", "Tim Cook");
linkMap.put("Microsoft", "Bill Gates");
linkMap.put("Amazon", "Jeff Bezos");
linkMap.put("Oracle", "Larry Ellison");
System.out.println("Before Sorting by Values -"
+ " as per insertion-order : \n");
// iterate original LinkedHashMap
for(Map.Entry<String, String> lhmap :
linkMap.entrySet()){
System.out.println("Key : " + lhmap.getKey()
+ "\t\t" + "Value : " + lhmap.getValue());
}
// 1. get entrySet from LinkedHashMap object
Set<Map.Entry<String, String>> companyFounderSet =
linkMap.entrySet();
// 2. convert LinkedHashMap to List of Map.Entry
List<Map.Entry<String, String>> companyFounderListEntry =
new ArrayList<Map.Entry<String, String>>(
companyFounderSet);
// 3. sort list of entries using Collections class'
// utility method sort(ls, cmptr)
Collections.sort(companyFounderListEntry,
new Comparator<Map.Entry<String, String>>() {
@Override
public int compare(Entry<String, String> es1,
Entry<String, String> es2) {
return es1.getValue().compareTo(es2.getValue());
}
});
// 4. clear original LinkedHashMap
linkMap.clear();
// 5. iterating list and storing in LinkedHahsMap
for(Map.Entry<String, String> map : companyFounderListEntry){
linkMap.put(map.getKey(), map.getValue());
}
System.out.println("\n\nSorted LinkedHashMap by its Values"
+ " in ascending-order\n");
// 6. iterate LinkedHashMap to retrieved stored values
for(Map.Entry<String, String> lhmap :
linkMap.entrySet()){
System.out.println("Key : " + lhmap.getKey()
+ "\t\t" + "Value : " + lhmap.getValue());
}
}
}
Output:
Before Sorting by Values - as per insertion-order :
Key : Google Value : Sundar Pichai
Key : Facebook Value : Mark Zuckerberg
Key : LinkedIn Value : Reid Hoffman
Key : Apple Inc Value : Tim Cook
Key : Microsoft Value : Bill Gates
Key : Amazon Value : Jeff Bezos
Key : Oracle Value : Larry Ellison
Sorted LinkedHashMap by its Values in ascending-order
Key : Microsoft Value : Bill Gates
Key : Amazon Value : Jeff Bezos
Key : Oracle Value : Larry Ellison
Key : Facebook Value : Mark Zuckerberg
Key : LinkedIn Value : Reid Hoffman
Key : Google Value : Sundar Pichai
Key : Apple Inc Value : Tim Cook
2. Sorting LinkedHashMap in descending order of Values :
2.1 Descending-order sorting steps :-
- get entrySet() from Map
- create/convert entry set into List of entries
- sort converted List using Collections class’ sort(); method by implementing Comparator for reverse sorting logic by its Values
- clear original LinkedHashMap using clear(); method
- Iterate List and add entries to original LinkedHashMap, after clearing
- finally print Map.Entry in console
2.2 Sorting LinkedHashMap by its values in descending-order :
- LinkedHashMap maintains insertion-order of keys
- In below illustration, we will sort/convert LinkedHashMap into reverse-ordering of Values i.e.; descending-order of values
SortingLinkedHashMapInDesOrderByValues.java
package in.bench.resources.collection;
import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.LinkedHashMap;
import java.util.List;
import java.util.Map;
import java.util.Set;
import java.util.Map.Entry;
public class SortingLinkedHashMapInDesOrderByValues {
public static void main(String[] args) {
// creating LinkedHashMap object of type <String, String>
Map<String, String> linkMap =
new LinkedHashMap<String, String>();
// adding key-value pairs to LinkedHashMap object
linkMap.put("Google", "Sundar Pichai");
linkMap.put("Facebook", "Mark Zuckerberg");
linkMap.put("LinkedIn", "Reid Hoffman");
linkMap.put("Apple Inc", "Tim Cook");
linkMap.put("Microsoft", "Bill Gates");
linkMap.put("Amazon", "Jeff Bezos");
linkMap.put("Oracle", "Larry Ellison");
System.out.println("Before Sorting by Values -"
+ " as per insertion-order : \n");
// iterate original LinkedHashMap
for(Map.Entry<String, String> lhmap :
linkMap.entrySet()){
System.out.println("Key : " + lhmap.getKey()
+ "\t\t" + "Value : " + lhmap.getValue());
}
// 1. get entrySet from LinkedHashMap object
Set<Map.Entry<String, String>> companyFounderSet =
linkMap.entrySet();
// 2. convert LinkedHashMap to List of Map.Entry
List<Map.Entry<String, String>> companyFounderListEntry =
new ArrayList<Map.Entry<String, String>>(
companyFounderSet);
// 3. sort list of entries using Collections class'
// utility method sort(ls, cmptr)
Collections.sort(companyFounderListEntry,
new Comparator<Map.Entry<String, String>>() {
@Override
public int compare(Entry<String, String> es1,
Entry<String, String> es2) {
return es2.getValue().compareTo(es1.getValue());
}
});
// 4. clear original LinkedHashMap
linkMap.clear();
// 5. iterating list and storing in LinkedHahsMap
for(Map.Entry<String, String> map : companyFounderListEntry){
linkMap.put(map.getKey(), map.getValue());
}
System.out.println("\n\nSorted LinkedHashMap by its Values"
+ " in descending-order\n");
// 6. iterate LinkedHashMap to retrieved stored values
for(Map.Entry<String, String> lhmap :
linkMap.entrySet()){
System.out.println("Key : " + lhmap.getKey()
+ "\t\t" + "Value : " + lhmap.getValue());
}
}
}
Output:
Before Sorting by Values - as per insertion-order :
Key : Google Value : Sundar Pichai
Key : Facebook Value : Mark Zuckerberg
Key : LinkedIn Value : Reid Hoffman
Key : Apple Inc Value : Tim Cook
Key : Microsoft Value : Bill Gates
Key : Amazon Value : Jeff Bezos
Key : Oracle Value : Larry Ellison
Sorted LinkedHashMap by its Values in descending-order
Key : Apple Inc Value : Tim Cook
Key : Google Value : Sundar Pichai
Key : LinkedIn Value : Reid Hoffman
Key : Facebook Value : Mark Zuckerberg
Key : Oracle Value : Larry Ellison
Key : Amazon Value : Jeff Bezos
Key : Microsoft Value : Bill Gates
Important points to remember about Map :
- HashMap stores entries (Key-Value pairs) in random-order of Keys
- LinkedHashMap stores entries (Key-Value pairs) as per insertion-order of Keys
- TreeMap stores entries (Key-Value pairs) in sorted-order of Keys
References:
- https://docs.oracle.com/javase/tutorial/collections/intro/
- https://docs.oracle.com/javase/tutorial/collections/interfaces/collection.html
- https://docs.oracle.com/javase/7/docs/api/java/util/Collection.html
- https://docs.oracle.com/javase/tutorial/collections/interfaces/list.html
- https://docs.oracle.com/javase/tutorial/collections/implementations/list.html
- https://docs.oracle.com/javase/8/docs/api/java/util/ArrayList.html
- https://docs.oracle.com/javase/tutorial/collections/interfaces/set.html
- https://docs.oracle.com/javase/7/docs/api/java/util/Set.html
- https://docs.oracle.com/javase/7/docs/api/java/util/HashSet.html
- https://docs.oracle.com/javase/7/docs/api/java/util/TreeSet.html
Happy Coding !!
Happy Learning !!
