The contains(E e) method of Deque Interface check for the presence of the element e in the Deque container. If the Deque contains one occurrence of the element, then it returns true else it returns false.
Syntax:
boolean contains(Object o)
Parameters: This method accepts a mandatory parameter o which is the element that needs to be tested if it is present in the Deque or not.
Return Value: The method returns True if the element is present in the Deque otherwise it returns False.
Exceptions: The function throws two exceptions as shown below:
- ClassCastException – if the type of the specified element is incompatible with this deque. It is optional.
- NullPointerException – if the specified element is null and this Deque does not permit null elements (optional). It is optional.
Below programs illustrate the contains() method in Java:
Program 1: With the help of LinkedList.
// Java code to illustrate contains()// method of Deque in Javaimport java.util.*;  public class GFG {    public static void main(String args[])    {        // Creating an empty Deque        Deque<String> de_que = new LinkedList<String>();          // Use add() method to add elements into the Queue        de_que.add("Welcome");        de_que.add("To");        de_que.add("Geeks");        de_que.add("4");        de_que.add("Geeks");          // Displaying the Deque        System.out.println("Deque: " + de_que);          // Check for "Geeks" in the deque        System.out.println("Does the deque contains 'Geeks'? "                           + de_que.contains("Geeks"));          // Check for "4" in the deque        System.out.println("Does the deque contains '4'? "                           + de_que.contains("4"));          // Check if the deque contains "No"        System.out.println("Does the deque contains 'No'? "                           + de_que.contains("No"));    }} |
Output:
Deque: [Welcome, To, Geeks, 4, Geeks] Does the deque contains 'Geeks'? true Does the deque contains '4'? true Does the deque contains 'No'? false
Program 2:
// Java code to illustrate contains()// method of Deque in Javaimport java.util.*;  public class GFG {    public static void main(String args[])    {        // Creating an empty Deque        Deque<Integer> de_que = new LinkedList<Integer>();          // Use add() method to add elements into the Queue        de_que.add(10);        de_que.add(15);        de_que.add(30);        de_que.add(20);        de_que.add(5);          // Displaying the Deque        System.out.println("Deque: " + de_que);          // Check for '15' in the Deque        System.out.println("Does the Deque contains '15'? "                           + de_que.contains(15));          // Check for '2' in the Deque        System.out.println("Does the Deque contains '2'? "                           + de_que.contains(2));          // Check if the Deque contains '10'        System.out.println("Does the Deque contains '10'? "                           + de_que.contains(10));    }} |
Output:
Deque: [10, 15, 30, 20, 5] Does the Deque contains '15'? true Does the Deque contains '2'? false Does the Deque contains '10'? true
Program 3: With the help of ArrayDeque.
// Java code to illustrate contains()// method of Deque in Javaimport java.util.*;  public class GFG {    public static void main(String args[])    {        // Creating an empty Deque        Deque<Integer> de_que = new ArrayDeque<Integer>();          // Use add() method to add elements into the Queue        de_que.add(10);        de_que.add(15);        de_que.add(30);        de_que.add(20);        de_que.add(5);          // Displaying the Deque        System.out.println("Deque: " + de_que);          // Check for '15' in the Deque        System.out.println("Does the Deque contains '15'? "                           + de_que.contains(15));          // Check for '2' in the Deque        System.out.println("Does the Deque contains '2'? "                           + de_que.contains(2));          // Check if the Deque contains '10'        System.out.println("Does the Deque contains '10'? "                           + de_que.contains(10));    }} |
Output:
Deque: [10, 15, 30, 20, 5] Does the Deque contains '15'? true Does the Deque contains '2'? false Does the Deque contains '10'? true
Program 4: With the help of ConcurrentLinkedDeque.
// Java code to illustrate contains()// method of Deque in Javaimport java.util.*;import java.util.concurrent.ConcurrentLinkedDeque;  public class GFG {    public static void main(String args[])    {        // Creating an empty Deque        Deque<Integer> de_que = new ConcurrentLinkedDeque<Integer>();          // Use add() method to add elements into the Queue        de_que.add(10);        de_que.add(15);        de_que.add(30);        de_que.add(20);        de_que.add(5);          // Displaying the Deque        System.out.println("Deque: " + de_que);          // Check for '15' in the Deque        System.out.println("Does the Deque contains '15'? "                           + de_que.contains(15));          // Check for '2' in the Deque        System.out.println("Does the Deque contains '2'? "                           + de_que.contains(2));          // Check if the Deque contains '10'        System.out.println("Does the Deque contains '10'? "                           + de_que.contains(10));    }} |
Output:
Deque: [10, 15, 30, 20, 5] Does the Deque contains '15'? true Does the Deque contains '2'? false Does the Deque contains '10'? true
Program 5: With the help of LinkedBlockingDeque.
// Java code to illustrate contains()// method of Deque in Javaimport java.util.*;import java.util.concurrent.LinkedBlockingDeque;  public class GFG {    public static void main(String args[])    {        // Creating an empty Deque        Deque<Integer> de_que = new LinkedBlockingDeque<Integer>();          // Use add() method to add elements into the Queue        de_que.add(10);        de_que.add(15);        de_que.add(30);        de_que.add(20);        de_que.add(5);          // Displaying the Deque        System.out.println("Deque: " + de_que);          // Check for '15' in the Deque        System.out.println("Does the Deque contains '15'? "                           + de_que.contains(15));          // Check for '2' in the Deque        System.out.println("Does the Deque contains '2'? "                           + de_que.contains(2));          // Check if the Deque contains '10'        System.out.println("Does the Deque contains '10'? "                           + de_que.contains(10));    }} |
Output:
Deque: [10, 15, 30, 20, 5] Does the Deque contains '15'? true Does the Deque contains '2'? false Does the Deque contains '10'? true
Note: The exceptions are compiler dependent, hence cannot be shown in the program.
Reference: https://docs.oracle.com/javase/8/docs/api/java/util/Deque.html#contains-java.lang.Object-
