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-