Introduction
Array Lists are part of the List interface in Java. They are very important because of the reason that they can grow or shrink easily depending on the need. So if we do not know the size of our data then it is better to use an Array List. They are not restricted by size.
Array List
- Array List is based on an array but different in the manner that it is resizable accordingly, unlike an array.
- Array List is not synchronized.
- Array List can grow or shrink accordingly.
- Array List is the part of the List interface in Java.
- Array List is synchronized; that is why they are not thread safe.
- Array List also allows null values.
Array List Methods
There are various methods. We will explain some of them.
Creation of Array List
ArrayList <List_name> = new ArrayList();
Example
package demo;
import java.util.*;
public class Demo
{
public static void main(String args[])
{
ArrayList ar = new ArrayList();
System.out.println("ArrayList is : " + ar);
}
}
Output
![creation of arraylist]()
Adding items into Array List
<List_name>.add("item");
Example
package demo;
import java.util.*;
public class Demo
{
public static void main(String args[])
{
ArrayList ar = new ArrayList();
ar.add("raj");
ar.add("ram");
System.out.println("ArrayList is : " + ar);
}
}
Output
![adding item into arraylist]()
Finding size of Array List
<List_name>.size( );
Example
package demo;
import java.util.*;
public class Demo
{
public static void main(String args[])
{
ArrayList ar = new ArrayList();
ar.add("raj");
ar.add("ram");
System.out.println("ArrayList is : " + ar);
System.out.println("Size of ArrayList is : " + ar.size());
}
}
Output
![size of arraylist]()
Retrieving item from Array List
<List_name>.get(index);
Example
package demo;
import java.util.*;
public class Demo
{
public static void main(String args[])
{
ArrayList ar = new ArrayList();
ar.add("raj");
ar.add("ram");
System.out.println("ArrayList is : " + ar);
for (int i = 0; i < ar.size(); i++)
{
System.out.println("At index : " + i +" item is " + ar.get(i));
}
}
}
Output
![retrieving item from arraylist]()
Removing item from Array List
<List_name>.remove(index);
Or:
<List_name>.remove("item");
Example
package demo;
import java.util.*;
public class Demo
{
public static void main(String args[])
{
ArrayList ar = new ArrayList();
ar.add("raj");
ar.add("ram");
ar.add("sam");
System.out.println("ArrayList is : " + ar);
ar.remove(1);
System.out.println("New ArrayList is " + ar);
}
}
Or:
package demo;
import java.util.*;
public class Demo
{
public static void main(String args[])
{
ArrayList ar = new ArrayList();
ar.add("raj");
ar.add("ram");
ar.add("sam");
System.out.println("ArrayList is : " + ar);
ar.remove("ram");
System.out.println("New ArrayList is " + ar);
}
}
Output
![removing item from arraylist]()
Removing all data from Array List
<List_name>.clear( );
Example
package demo;
import java.util.*;
public class Demo
{
public static void main(String args[])
{
ArrayList ar = new ArrayList();
ar.add("raj");
ar.add("ram");
ar.add("sam");
System.out.println("ArrayList is : " + ar);
ar.clear();
System.out.println("ArrayList is : " + ar);
}
}
Output
![clearing data from arraylist]()
Checking Array List
<List_name>.contains("item");
Example
package demo;
import java.util.*;
public class Demo
{
public static void main(String args[])
{
ArrayList ar = new ArrayList();
ar.add("raj");
ar.add("ram");
ar.add("sam");
System.out.println("ArrayList is : " + ar);
boolean b = ar.contains("ram");
System.out.println(b);
}
}
Output
![checking arraylist]()
Finding index of an item in Array List
<List_name>.indexOf("item");
Example
package demo;
import java.util.*;
public class Demo
{
public static void main(String args[])
{
ArrayList ar = new ArrayList();
ar.add("raj");
ar.add("ram");
ar.add("sam");
System.out.println("ArrayList is : " + ar);
System.out.println("Index of ram is : " + ar.indexOf("ram"));
}
}
Output
![finding index of item]()
Checking for empty Array List
if(<List_name>.size() == 0)
{
System.out.println("Empty Array List");
}
Example
package demo;
import java.util.*;
public class Demo
{
public static void main(String args[])
{
ArrayList ar = new ArrayList();
if(ar.size() == 0)
{
System.out.println("Empty Array List");
}
}
}
Output
![empty array list]()
Replacing item in Array List
<List_name>.set(index, "new item");
Example
package demo;
import java.util.*;
public class Demo
{
public static void main(String args[])
{
ArrayList ar = new ArrayList();
ar.add("raj");
ar.add("ram");
ar.add("sam");
System.out.println("ArrayList is : " + ar);
ar.set(1, "rambo");
System.out.println("ArrayList is : " + ar);
}
}
Output
![replacing item from arraylist]()
Summary
This article explains the Array List in Java and various Array List methods in Java.