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Program: Write a program to implement ArrayList.

Write a program to implement your own ArrayList class. It should
contain add(), get(), remove(), size() methods. Use dynamic array logic.
It should increase its size when it reaches threshold.

package com.java2novice.algos;

import java.util.Arrays;

public class MyArrayList {

	private Object[] myStore;
	private int actSize = 0;
	public MyArrayList(){
		myStore = new Object[10];
	public Object get(int index){
		if(index < actSize){
			return myStore[index];
		} else {
			throw new ArrayIndexOutOfBoundsException();
	public void add(Object obj){
		if(myStore.length-actSize <= 5){
		myStore[actSize++] = obj;
	public Object remove(int index){
		if(index < actSize){
			Object obj = myStore[index];
			myStore[index] = null;
			int tmp = index;
			while(tmp < actSize){
				myStore[tmp] = myStore[tmp+1];
				myStore[tmp+1] = null;
			return obj;
		} else {
			throw new ArrayIndexOutOfBoundsException();
	public int size(){
		return actSize;
	private void increaseListSize(){
		myStore = Arrays.copyOf(myStore, myStore.length*2);
		System.out.println("\nNew length: "+myStore.length);
	public static void main(String a[]){
		MyArrayList mal = new MyArrayList();
		mal.add(new Integer(2));
		mal.add(new Integer(5));
		mal.add(new Integer(1));
		mal.add(new Integer(23));
		mal.add(new Integer(14));
		for(int i=0;i<mal.size();i++){
			System.out.print(mal.get(i)+" ");
		mal.add(new Integer(29));
		System.out.println("Element at Index 5:"+mal.get(5));
		System.out.println("List size: "+mal.size());
		System.out.println("Removing element at index 2: "+mal.remove(2));
		for(int i=0;i<mal.size();i++){
			System.out.print(mal.get(i)+" ");

2 5 1 23 14 
New length: 20
Element at Index 5:29
List size: 6
Removing element at index 2: 1
2 5 23 14 29 
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List Of All Interview Programs:

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  10. Write a program to implement ArrayList.
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  15. Write a program to find common elements between two arrays.
  16. How to swap two numbers without using temporary variable?
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  18. Write a program to find sum of each digit in the given number using recursion.
  19. Write a program to check the given number is a prime number or not?
  20. Write a program to find the given number is Armstrong number or not?
  21. Write a program to convert binary to decimal number.
  22. Write a program to check the given number is binary number or not?
  23. Write a program for Bubble Sort in java.
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  25. Write a program to implement hashcode and equals.
  26. How to get distinct elements from an array by avoiding duplicate elements?
  27. Write a program to get distinct word list from the given file.
  28. Write a program to get a line with max word count from the given file.
  29. Write a program to convert string to number without using Integer.parseInt() method.
  30. Write a program to find two lines with max characters in descending order.
  31. Write a program to find the sum of the first 1000 prime numbers.
  32. Find longest substring without repeating characters.
  33. Write a program to remove duplicates from sorted array.
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Knowledge Centre
When to use LinkedList or ArrayList?
Accessing elements are faster with ArrayList, because it is index based. But accessing is difficult with LinkedList. It is slow access. This is to access any element, you need to navigate through the elements one by one. But insertion and deletion is much faster with LinkedList, because if you know the node, just change the pointers before or after nodes. Insertion and deletion is slow with ArrayList, this is because, during these operations ArrayList need to adjust the indexes according to deletion or insetion if you are performing on middle indexes. Means, an ArrayList having 10 elements, if you are inserting at index 5, then you need to shift the indexes above 5 to one more.
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About Author

I'm Nataraja Gootooru, programmer by profession and passionate about technologies. All examples given here are as simple as possible to help beginners. The source code is compiled and tested in my dev environment.

If you come across any mistakes or bugs, please email me to [email protected] or you can comment on the page.

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Reference: Java™ Platform Standard Ed. 7 - API Specification | Java is registered trademark of Oracle.
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