Collection contains() method in Java with Examples

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);
    }
}

Output:

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);
    }
}

Output:

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);
    }
}

Output:

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);
        }
    }
}

Output:

The ArrayList is: []

Reference: https://docs.oracle.com/javase/9/docs/api/java/util/Collection.html#contains-java.lang.Object-