Collection add() Method in Java with Examples
Last Updated :
07 Oct, 2022
The add(E element) of java.util.Collection interface is used to add the element ‘element’ to this collection. This method returns a boolean value depicting the successfulness of the operation. If the element was added, it returns true, else it returns false.
Syntax:
Collection.add(E element)
Parameters: This method accepts a mandatory parameter element of type E which is to be added to this collection.
Return Value: A boolean value depicting the successfulness of the operation. If the element was added, it returns true, else it returns false.
Exceptions: This method throws 5 following exceptions listed below as follows:
- UnsupportedOperationException: if the add operation is not supported by this collection
- 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
- IllegalArgumentException: if some property of the element prevents it from being added to this collection
- IllegalStateException: if the element cannot be added at this time due to insertion restrictions
Now we will be implementing this method over different classes as it is a very important and essential method when it comes downs to java programming so here we will be stressing over each class as follows:
- LinkedList class
- ArrayDeque
- ArrayList class
- NullPointerException is Thrown
Let us implement add() method in all 4 above listed cases via clean java examples as follows:
Example 1: LinkedList Class
Java
import java.io.*;
import java.util.*;
public class GFG {
public static void main(String args[])
{
Collection<String> list = new LinkedList<String>();
list.add( "Geeks" );
list.add( "for" );
list.add( "Geeks" );
System.out.println( "The list is: " + list);
list.add( "Last" );
list.add( "Element" );
System.out.println( "The new List is: " + list);
}
}
|
Output:
The list is: [Geeks, for, Geeks]
The new List is: [Geeks, for, Geeks, Last, Element]
Example 2: ArrayDeque Class
Java
import java.util.*;
public class ArrayDequeDemo {
public static void main(String args[])
{
Collection<String> de_que = new ArrayDeque<String>();
de_que.add( "Welcome" );
de_que.add( "To" );
de_que.add( "Geeks" );
de_que.add( "4" );
de_que.add( "Geeks" );
System.out.println( "ArrayDeque: " + de_que);
}
}
|
Output:
ArrayDeque: [Welcome, To, Geeks, 4, Geeks]
Example 3: Using ArrayList Class
Java
import java.io.*;
import java.util.*;
public class ArrayListDemo {
public static void main(String[] args)
{
Collection<Integer> arrlist = new ArrayList<Integer>( 5 );
arrlist.add( 15 );
arrlist.add( 20 );
arrlist.add( 25 );
for (Integer number : arrlist) {
System.out.println( "Number = " + number);
}
}
}
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Output:
Number = 15
Number = 20
Number = 25
Geeks do keep an bound over special case where NullPointer Exception will be thrown as show in below example as follows:
Example 4:
Java
import java.util.*;
class GFG {
public static void main(String args[])
{
Collection<String> list = new ArrayList<String>();
System.out.println( "The ArrayList is: " + list);
try {
list.add( null );
}
catch (Exception e) {
System.out.println( "Exception: " + e);
}
}
}
|
Output:
The ArrayList is: []
Output explanation: Here we need to pick it up as we will only receive a List. So it is good practice to document for add() method either it is accepting it whether it needs to support null.
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