The contains(Object element) of java.util.Collection interface is used to check whether the element ‘element’ exists in this collection. This method returns a boolean value depicting the presence of the element. If the element is present, it returns true, else it returns false.
Syntax:
Collection.contains(Object element)
Parameters: This method accepts a mandatory parameter element of type Object which is to be checked in this collection.
Return Value: This method returns a boolean value depicting the presence of the element. If the element is added, it returns true, else it returns false.
Exceptions: This method throws following exceptions:
- ClassCastException: if the class of the specified element prevents it from being added to this collection
- NullPointerException: if the specified element is null and this collection does not permit null elements
Below examples illustrate the Collection contains() method:
Example 1: Using LinkedList Class
// Java code to illustrate boolean contains() method import java.io.*;import java.util.*; public class GFG { public static void main(String args[]) { // creating an empty LinkedList Collection<String> list = new LinkedList<String>(); // use add() method to add elements in the list list.add("Geeks"); list.add("for"); list.add("Geeks"); // Output the present list System.out.println("The list is: " + list); // Checking the presence of Geeks // using contains() method boolean result = list.contains("Geeks"); // printing the result System.out.println("Is Geeks present in the List: " + result); }} |
The list is: [Geeks, for, Geeks] Is Geeks present in the List: true
Example 2: Using ArrayDeque Class
// Java code to illustrate contains() method import java.util.*; public class ArrayDequeDemo { public static void main(String args[]) { // Creating an empty ArrayDeque Collection<String> de_que = new ArrayDeque<String>(); // Use add() method to add elements into the Deque de_que.add("Welcome"); de_que.add("To"); de_que.add("Geeks"); de_que.add("4"); de_que.add("Geeks"); // Displaying the ArrayDeque System.out.println("ArrayDeque: " + de_que); // Checking the presence of Geeks // using contains() method boolean result = de_que.contains("Geeks"); // printing the result System.out.println("Is Geeks present in the ArrayDeque: " + result); }} |
ArrayDeque: [Welcome, To, Geeks, 4, Geeks] Is Geeks present in the ArrayDeque: true
Example 3: Using ArrayList Class
// Java code to illustrate contains() method import java.io.*;import java.util.*; public class ArrayListDemo { public static void main(String[] args) { // create an empty array list with an initial capacity Collection<Integer> arrlist = new ArrayList<Integer>(5); // use add() method to add elements in the list arrlist.add(15); arrlist.add(20); arrlist.add(25); // Output the present list System.out.println("ArrayList: " + arrlist); // Checking the presence of 20 // using contains() method boolean result = arrlist.contains(20); // printing the result System.out.println("Is 20 present in the ArrayList: " + result); }} |
ArrayList: [15, 20, 25] Is 20 present in the ArrayList: true
Example 4: To demonstrate NullPointer Exception
// Java code to illustrate boolean contains() import java.util.*; public class LinkedListDemo { public static void main(String args[]) { // Creating an empty ArrayList Collection<String> list = new ArrayList<String>(); // Displaying the list System.out.println("The ArrayList is: " + list); try { // Checking presence of null list.contains(null); } catch (Exception e) { System.out.println("Exception: " + e); } }} |
The ArrayList is: []
Reference: https://docs.oracle.com/javase/9/docs/api/java/util/Collection.html#contains-java.lang.Object-
