Collection contains() method in Java with Examples

29 Nov, 2018
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-
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