TreeMap’s addAll method to sort java Collection framework classes

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If elements are stored in stored in HashSet/ArrayList or any other class that implements Collection  we can use TreeSet’s addAll for sorting.

Let’s see Example >

Collection-

Collection<Integer> collection = new HashSet<Integer>();       collection.add(3);       collection.add(1);       collection.add(2);

TreeSet’s  addAll method -

Set<Integer> treeSet = new TreeSet<Integer>();       treeSet.addAll(collection);

Full program -

import java.util.Collection; import java.util.HashSet; import java.util.Set; import java.util.TreeSet; /** * @author AnkitMittal * Copyright (c), AnkitMittal JavaMadeSoEasy.com * Main class */ public class SortSet {   public static void main(String...a){       Collection<Integer> collection = new HashSet<Integer>();       collection.add(3);       collection.add(1);       collection.add(2);       //TreeSet's addAll       Set<Integer> treeSet = new TreeSet<Integer>();       treeSet.addAll(collection);       System.out.println("treeSet : "+treeSet);         } } /*OUTPUT treeSet : [1, 2, 3] */

Important Note :

1. If any class that implements  Collection contains null  - If any class that implements  Collection contains null  and is converted into TreeSet than NullPointerException (RunTimeException) will be thrown.
2. If any class that implements List is converted into TreeSet -  Than that class’s duplicate elements will be lost, because any of the Set implementation ( TreeSet or may be any other class) does not allow to store duplicate elements.

RELATED LINKS>

Program to sort Employee list on basis of name in ascending order by implementing Comparable interface and overriding its compareTo method

Program to sort Integer array using Arrays.sort (by default Arrays.sort will sort array in ascending order)

Labels: Collection programs Core Java