May 18, 2017

Sreekanth B

Write a Program To Implement ArrayList Java Program


Program: 

Write a program to implement ArrayList.

Description:

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.

Code:

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){
            increaseListSize();
        }
        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;
                tmp++;
            }
            actSize--;
            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)+" ");
        }
    }
}

Output:

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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