Here the Below Example will show you how you can construct your own Collection(ArrayList) in Java. The below example will show you that our Class Generics will behave like the ArrayList. I have use the Generic Programming to Implement the concepts and this blog will give you the core idea how you can create your own collection framework . This is not complete implementation as like ArrayList but it gives you the idea when you want to implement the functionality like ArrayList Class or makes your own Collections classes.

package com.util;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import java.util.Vector;

public class Generics<T> {
    private int i=0;
    private Object obj[];
    private T t;

    public Generics()
    {

        obj=new Object[5];

    }

    public void add(T t)
    {
        this.t=t;

        if(i==obj.length-1)
        {
            //Increase the Capacity of Array by 50% of it's size
            obj=Arrays.copyOf(obj, obj.length+(obj.length/2));

            System.out.println(obj.length);
        }

        obj[i]=this.t;
        i++;

    }

    public Object get(int i)
    {

        if(obj[i]!=null)
        {
            return obj[i];
        }
        else
        {
            throw new ArrayIndexOutOfBoundsException("index:"+i);
        }

    }

    public String toString()
    {
        String temp="";
        for(Object ob:obj)
        {
            if(ob!=null)
            {

                temp=temp+ob+',';
            }


        }

        String temp1=temp.substring(0, temp.length()-1);




        return "["+temp1+"]";
    }

    /**
     * @param args
     */
    public static void main(String[] args) {
        // TODO Auto-generated method stub

        Generics<Integer> genList=new Generics<Integer>();
        Generics<String> gen1List=new Generics<String>();
        genList.add(12);
        genList.add(23);
        genList.add(25);


        gen1List.add("manish");
        gen1List.add("akki");


        System.out.println(genList+"  "+gen1List);








    }

}