Array List is a class present in java.util package and is a part of Java Collecation Framework. ArrayList is implemented using a dynamic array data structure to store objects, hence it can grow or shrink whenever you add or remove elements from it. Here is an example of the implementation of custom ArrayList in java with the basic functions of the ArrayList class.
Also see: How to iterate ArrayList
Here the user-defined ArrayList class performs add[], addAll[], get[], set[], remove[], and a few more functionalities as listed below.
Implementation of Custom ArrayList with the following functionalities.
- add[Object o]
- add[int index, Object o]
- addAll[Collection c]
- remove[Object o]
- get[int index]
- set[int index, Object o]
- contains[Object o]
- size[]
- isEmpty[]
- clear[]
Java Source Code For Custom ArrayList:
MyArrayList.java
package javaCodeKorner.collection.ArrayList.userDefinedArrayList;
import java.util.Collection;
public class MyArrayList
{
private int size=0;
private int capacity=10;
private Object[] arr;
//Creates empty ArrayList with default capacity 10
public MyArrayList[]
{
arr = new Object[capacity];
}
//Creates empty ArrayList with specified initial capacity
public MyArrayList[int arg]
{
this.capacity=arg;
arr = new Object[capacity];
}
/**Inserts the specified element at the end of the list
* @param arg element to be added
* @return true after successful insertion
*/
public boolean add[Object arg]
{
if [size 0]
System.arraycopy[arr, i+1, arr, i,numMoved];
arr[--size]=null;
return true;
}
}
}
else
for [int i = 0; i < size; i++]
{
if [arr[i].equals[o]]
{
int numMoved = size - i - 1;
if [numMoved > 0]
System.arraycopy[arr, i+1, arr, i,numMoved];
arr[--size]=null;
return true;
}
}
return false;
}
/**Returns the specified element
*
* @param index
* @return element at the specified position
*/
public Object get[int index]
{
if [index>=this.size]
{
throw new IndexOutOfBoundsException[];
}
return arr[index];
}
/**Replaces the element at the specified position in this list
* with the specified element.
* @param index
* @param element
* @return Object previous Object
*/
public Object set[int index, Object obj]
{
Object oldElement = arr[index];
arr[index] = obj;
return oldElement;
}
/**Returns true if list contains specified element
* else returns false
* @param o element whose presence in the list is to be checked */
public boolean contains[Object o]
{
for [int i = 0; i < size; i++]
{
if [arr[i].equals[o]]
{
return true;
}
}
return false;
}
/**Returns the size of the list*/
public int size[]
{
return size;
}
/**Returns true if list contains no elements
* @return true if list is empty
*/
public boolean isEmpty[]
{
if [size==0]
{
return true;
}
else
return false;
}
/**Removes all the elements from the list*/
public void clear[]
{
arr = new Object[capacity];
size=0;
}
}
Below are test classes to add, remove, set, get, etc. from the MyArrayList:
Example for add[] method
AddElements.java
public class AddElements
{
public static void main[String[] args]
{
MyArrayList list = new MyArrayList[];
list.add["123"];
list.add[123.456];
list.add["Naveen"];
list.add["Ravi"];
//Adding element at the specific position
list.add[4, "Rajesh"];
//Iterating list by for-loop
for [int i = 0; i < list.size[]; i++]
{
System.out.println[list.get[i]];
}
}
}
Output:123
123.456
Naveen
Ravi
Rajesh
Example For remove[] method.
RemoveElements.java
public class RemoveElements
{
public static void main[String[] args]
{
MyArrayList list = new MyArrayList[];
list.add["Rakesh"];
list.add["Mahesh"];
list.add["Naveen"];
list.add["Ravi"];
//Adding element at the specific position
list.add[4, "Rajesh"];
System.out.println["Before removing"];
System.out.println["size:"+list.size[]];
for [int i = 0; i < list.size[]; i++]
{
System.out.println[list.get[i]];
}
//Removing specified element
list.remove["Naveen"];
System.out.println["*****************"];
System.out.println["After removing"];
System.out.println["size:"+list.size[]];
for [int i = 0; i < list.size[]; i++]
{
System.out.println[list.get[i]];
}
}
}
Before removing
size:5
Rakesh
Mahesh
Naveen
Ravi
Rajesh
*****************
After removing
size:4
Rakesh
Mahesh
Ravi
Rajesh
Example for get[] and set[] methods.
GetAndSetDemo.java
public class GetAndSetDemo
{
public static void main[String[] args]
{
MyArrayList list = new MyArrayList[];
list.add["Rakesh"];
list.add["Mahesh"];
list.add["Naveen"];
list.add["Ravi"];
System.out.println["Before update: "+list.get[1]];
//Replacing an element at a specified index
list.set[1, "Kumar"];
System.out.println["After update: "+list.get[1]];
}
}
Output:Before update: Mahesh
After update: Kumar
Example for contains[], isEmpty[], size[] methods.
MyArrayListDemo.java
public class MyArrayListDemo
{
public static void main[String[] args]
{
MyArrayList list = new MyArrayList[];
list.add["Rakesh"];
list.add["Mahesh"];
list.add["Naveen"];
list.add["Ravi"];
System.out.println["contains: "+list.contains["Mahesh"]];
System.out.println["isEmpty: "+list.isEmpty[]];
System.out.println["size, before clearing: "+list.size[]];
list.clear[];//clearing array
System.out.println["size, after clearing: "+list.size[]];
}
}
Output:contains: true
isEmpty: false
size, before clearing: 4
size, after clearing: 0
See Also:
- How to sort ArrayList in java
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