Java program to compare elements in a collection

In Java, the Collection framework provides an architecture to store and manipulate a group of objects. Collections support operations such as searching, sorting, insertion, manipulation, and deletion.

In this article, we will learn how to compare elements in a collection in Java using different approaches. Before learning about the methods, let us understand the problem with the help of the following input-output scenarios:

Scenario 1

Input: ["Java", "Python", "JavaScript", "C++"] Element to Compare: "Java" Output: Java is equal to Java Python is not equal to Java JavaScript is not equal to Java C++ is not equal to Java 

Scenario 2

Input: ["Apple", "Banana", "Mango", "Orange"] Element to Compare: "Mango" Output: Apple is not equal to Mango Banana is not equal to Mango Mango is equal to Mango Orange is not equal to Mango 

The following are the approaches to compare elements in a collection in Java:

• Using equals() Method
• Using Comparator

Comparing Elements in a Collection Using equals() Method

The equals() method is used to compare two objects for equality. It returns true if the objects are equal, otherwise false. We can use this method to compare elements in a collection.

Example

In the following example, we compare each element of a collection of strings with a given string using the equals() method:

import java.util.ArrayList; import java.util.List; public class CompareElements { public static void main(String[] args) { List<String> list = new ArrayList<>(); list.add("Java"); list.add("Python"); list.add("JavaScript"); list.add("C++"); String elementToCompare = "Java"; for (String element : list) { if (element.equals(elementToCompare)) { System.out.println(element + " is equal to " + elementToCompare); } else { System.out.println(element + " is not equal to " + elementToCompare); } } } } 

Output

Java is equal to Java Python is not equal to Java JavaScript is not equal to Java C++ is not equal to Java 

Comparing Elements in a Collection Using Comparator

The Comparator interface in Java is used to compare two objects. It provides the compare() method, which compares two objects and returns an integer value. We can use this interface to compare elements in a collection.

Syntax:

int compare(T o1, T o2); 

Example

In the following example, we create a custom comparator to compare elements in a collection and sort them based on the comparison:

import java.util.ArrayList; import java.util.Collections; import java.util.Comparator; import java.util.List; public class CompareElementsUsingComparator { public static void main(String[] args) { List<String> list = new ArrayList<>(); list.add("Java"); list.add("Python"); list.add("JavaScript"); list.add("C++"); Collections.sort(list, new Comparator<String>() { @Override public int compare(String o1, String o2) { return o1.compareTo(o2); } }); System.out.println("Sorted List: " + list); } } 

Output

Sorted List: [C++, Java, JavaScript, Python]