Question

In Java: Create an addBefore and add method to the class IntArrayList. The method addBefore adds an element to the beginning of an array, at index 0, causing all existing elements to move forward (their indexes increased by 1). The method add creates an element at the end of the array. There are several ways to accomplish this task. Perhaps the easiest: double the array when you hit the beginning or end, copying it to the beginning or end dependent on if you're in the add or addBefore method.

Answer 1

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//IntArrayList.java file

class IntArrayList

{

//declare array of int array

private int []array;

//declare a variable to hold current size of array

private int currentSize;

private int capacity;

//declare constructor without parameter

public IntArrayList()

{

//declare the default capacity 5

array=new int[5];

currentSize=0;

capacity=5;

}

//double the size when default capacity is less to accomadate the array elements

public void doubleSize()

{

int []Temparray=new int[2*capacity];

//update new capacity

capacity=2*capacity;

//copy all the elements from IntArray to Temp array

for(int i = 0; i < currentSize; i++)

{

Temparray[i]=array[i];

}

//now assign the Temparray to IntArray

array=Temparray;

}

//addBefore method, add the element at the beginning of the array ,ie at the index 0

public void addBefore(int val)

{

//check if capacity of the array can accomodate the new element

if((currentSize+1) >= capacity )

{

//double the array size

doubleSize();

}

if(currentSize == 0) //IntArray is empty

{

array[0]=val;

++currentSize;

return ;

}

//push elements from 0 to the right , ie element at index 0 is pushed to index 1 , element at index 1 pushed down to index 2 and so on

for(int i =currentSize; i>0; i-- )

{

array[i]=array[i-1];

//System.out.println(""+array[i]);

}

//now assign the value to index 0

array[0]=val;

++currentSize;

}

//add method,adds element at the end of the array

public void add(int val)

{

if((currentSize+1) >= capacity)

{

doubleSize();

}

array[currentSize++]=val;

}

//helper method to display array elements

public void print()

{

System.out.println("Array elemensts are: ");

for(int i = 0; i < currentSize; i++)

{

System.out.println(""+array[i]);

}

}

}

==============================================================

//Main.java file

class Main {

public static void main(String[] args) {

//System.out.println("Hello world!");

//declare object of IntArrayList

IntArrayList intList = new IntArrayList();

// add elemenst using addBefore method

intList.addBefore(6);

intList.addBefore(5);

intList.addBefore(4);

intList.addBefore(3);

intList.addBefore(2);

intList.addBefore(1);

//print list

intList.print();

//add elements at the end of array

intList.add(7);

intList.add(8);

intList.add(9);

intList.add(10);

intList.add(11);

//print list

intList.print();

}

}

==========================

//output

Array elemensts are:
1
2
3
4
5
6
Array elemensts are:
1
2
3
4
5
6
7
8
9
10
11