In this article, we will discuss how to convert ordered LinkedHashMap into Sorted TreeMap by its Keys
Sorting LinkedHashMap in both Ascending/descending order by its Keys:
- Ascending order: pass LinkedHashMap entries as arguments to TreeMap class’ inter-conversion constructor
- Descending order: Implement Comparator interface by providing reverse sorting logic and finally putting all entries of HashMap into TreeMap classs using putAll(); method
Example 1: Sorting in ascending order of keys:
- LinkedHashMap maintains insertion-order
- In below demo example, we will sort/convert LinkedHashMap into natural-ordering of keys i.e.; ascending-order of keys
Syntax:
// convert to TreeMap Map<String, String> ts = new TreeMap<String, String>(linkMap);
SortingLinkedHashMapInAscOrder.java
package in.bench.resources.collection;
import java.util.LinkedHashMap;
import java.util.Iterator;
import java.util.Map;
import java.util.Set;
import java.util.TreeMap;
public class SortingLinkedHashMapInAscOrder {
public static void main(String[] args) {
// creating LinkedHashMap object of type <String, String>
LinkedHashMap<String, String> linkMap =
new LinkedHashMap<String, String>();
// adding key-value pairs to LinkedHashMap object
linkMap.put("Microsoft", "Bill Gates");
linkMap.put("Apple", "Steve Jobs");
linkMap.put("Google", "Sundar Pichai");
linkMap.put("LinkedIn", "Reid Hoffman");
linkMap.put("Facebook", "Mark Zuckerberg");
// Insertion-Order iterating
System.out.println("Before Sorting : Insertion-Order \n");
// getting keySet() into Set
Set<String> set = linkMap.keySet();
// get Iterator from key set
Iterator<String> itr = set.iterator();
// iterating in Insertion-order
while(itr.hasNext()) {
String key = itr.next();
System.out.println("Key : " + key
+ "\t\t" + "Value : " + linkMap.get(key));
}
// After Sorting : Ascending order
System.out.println("\n\n\nAfter Sorting : Ascending-Order\n");
// convert to TreeMap
Map<String, String> ts = new TreeMap<String, String>(linkMap);
// iterate acc to ascending order of keys
for(String strKey : ts.keySet()){
System.out.println("Key : " + strKey
+ "\t\t" + "Value : " + linkMap.get(strKey));
}
}
}
Output:
Before Sorting : Insertion-Order Key : Microsoft Value : Bill Gates Key : Apple Value : Steve Jobs Key : Google Value : Sundar Pichai Key : LinkedIn Value : Reid Hoffman Key : Facebook Value : Mark Zuckerberg After Sorting : Ascending-Order Key : Apple Value : Steve Jobs Key : Facebook Value : Mark Zuckerberg Key : Google Value : Sundar Pichai Key : LinkedIn Value : Reid Hoffman Key : Microsoft Value : Bill Gates
Example 2: Sorting in descending order of keys:
- LinkedHashMap maintains insertion-order
- In below demo example, we will sort/convert LinkedHashMap into reverse-ordering of keys i.e.; descending-order of keys
Syntax:
// convert to TreeMap
// descending or reverse-order sorting logic
Map<String, String> tMap = new TreeMap<String, String>(
new Comparator<String>() {
@Override
public int compare(String str1, String str2) {
return str2.compareTo(str1);
}
});
// put all key-value into TreeMap
tMap.putAll(linkMap);
SortingLinkedHashMapInDesOrder.java
package in.bench.resources.collection;
import java.util.Comparator;
import java.util.Iterator;
import java.util.LinkedHashMap;
import java.util.Map;
import java.util.Set;
import java.util.TreeMap;
public class SortingLinkedHashMapInDesOrder {
public static void main(String[] args) {
// creating LinkedHashMap object of type <String, String>
LinkedHashMap<String, String> linkMap =
new LinkedHashMap<String, String>();
// adding key-value pairs to LinkedHashMap object
linkMap.put("Microsoft", "Bill Gates");
linkMap.put("Apple", "Steve Jobs");
linkMap.put("Google", "Sundar Pichai");
linkMap.put("LinkedIn", "Reid Hoffman");
linkMap.put("Facebook", "Mark Zuckerberg");
// Insertion-Order iterating
System.out.println("Before Sorting : Insertion-Order \n");
// getting keySet() into Set
Set<String> set = linkMap.keySet();
// get Iterator from key set
Iterator<String> itr = set.iterator();
// iterating in insertion-order
while(itr.hasNext()) {
String key = itr.next();
System.out.println("Key : " + key
+ "\t\t" + "Value : " + linkMap.get(key));
}
// After Sorting : Descending order
System.out.println("\n\n\nAfter Sorting : Descending-Order\n");
// convert to TreeMap
// descending or reverse-order sorting logic
Map<String, String> tMap = new TreeMap<String, String>(
new Comparator<String>() {
@Override
public int compare(String str1, String str2) {
return str2.compareTo(str1);
}
});
// put all key-value into TreeMap
tMap.putAll(linkMap);
// iterate acc to descending order of keys
for(String strKey : tMap.keySet()){
System.out.println("Key : " + strKey
+ "\t\t" + "Value : " + linkMap.get(strKey));
}
}
}
Output:
Before Sorting : Insertion-Order Key : Microsoft Value : Bill Gates Key : Apple Value : Steve Jobs Key : Google Value : Sundar Pichai Key : LinkedIn Value : Reid Hoffman Key : Facebook Value : Mark Zuckerberg After Sorting : Descending-Order Key : Microsoft Value : Bill Gates Key : LinkedIn Value : Reid Hoffman Key : Google Value : Sundar Pichai Key : Facebook Value : Mark Zuckerberg Key : Apple Value : Steve Jobs
Important points:
- HashMap stores entries (key-value pairs) in random-order
- LinkedHashMap stores entries (key-value pairs) as per insertion-order
- TreeMap stores entries (key-value pairs) in some sorting-order
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/7/docs/api/java/util/ArrayList.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/class-use/HashSet.html
- https://docs.oracle.com/javase/7/docs/api/java/util/HashSet.html
- http://docs.oracle.com/javase/6/docs/api/java/util/TreeSet.html
- https://docs.oracle.com/javase/7/docs/api/java/util/TreeSet.html
Happy Coding !!
Happy Learning !!