Java Collections

Sorting in collection framework

We can sort the elements of:
  1. String objects
  2. Wrapper class objects
  3. User-defined class objects

Collections class provides static methods for sorting the elements of collection.If collection elements are of Set type, we can use TreeSet. But We cannot sort the elements of List. Collections class provides methods for sorting the elements of List type elements.
Method of Collections class for sorting List elements
public void sort(List list): is used to sort the elements of List. List elements must be of Comparable type.

Note: String class and Wrapper classes implements the Comparable interface. So if you store the objects of string or wrapper classes, it will be Comparable.

Example of Sorting the elements of List that contains string objects-

import java.util.*;
class Simple12{
public static void main(String args[]){

ArrayList al=new ArrayList();
al.add("Dinesh");
al.add("Sweetu");
al.add("Adesh");
al.add("Vinesh");

Collections.sort(al);
Iterator itr=al.iterator();

while(itr.hasNext()){
System.out.println(itr.next());
 }
}

}

Output:
Adesh
Dinesh
Sweetu
Vinesh

Example of Sorting the elements of List that contains Wrapper class objects

import java.util.*;
class Simple12{
public static void main(String args[]){

ArrayList al=new ArrayList();
al.add(Integer.valueOf(201));
al.add(Integer.valueOf(101));
al.add(230);//internally will be converted into objects as Integer.valueOf(230)

Collections.sort(al);

Iterator itr=al.iterator();
while(itr.hasNext()){
System.out.println(itr.next());
 }
}
}

Output:
101
201
230

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Dinesh Rajput

Dinesh Rajput is the chief editor of a website Dineshonjava, a technical blog dedicated to the Spring and Java technologies. It has a series of articles related to Java technologies. Dinesh has been a Spring enthusiast since 2008 and is a Pivotal Certified Spring Professional, an author of a book Spring 5 Design Pattern, and a blogger. He has more than 10 years of experience with different aspects of Spring and Java design and development. His core expertise lies in the latest version of Spring Framework, Spring Boot, Spring Security, creating REST APIs, Microservice Architecture, Reactive Pattern, Spring AOP, Design Patterns, Struts, Hibernate, Web Services, Spring Batch, Cassandra, MongoDB, and Web Application Design and Architecture. He is currently working as a technology manager at a leading product and web development company. He worked as a developer and tech lead at the Bennett, Coleman & Co. Ltd and was the first developer in his previous company, Paytm. Dinesh is passionate about the latest Java technologies and loves to write technical blogs related to it. He is a very active member of the Java and Spring community on different forums. When it comes to the Spring Framework and Java, Dinesh tops the list!

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