Arrays in Java | Edureka

Array in Java
Types of Arrays
Topics For Today’s Discussion
JAVA CERTIFICATION TRAINING www.edureka.co/java-j2ee-soa-training
Topics for Today’s Session
DeclaringAccessingUpdatingCreatingWorking with Array
Sorting in Arrays
Searching in Arrays

Java Array
Array is a static
Data Structure
Contains
collections of
homogenous
elements
All the
elements are
stored under
one variable
name
It occupies a
contiguous
memory location

Types Of Arrays
01Single
Dimensional
Single Dimensional or
1-D array is a type of
linear array in which
elements are stored in
a continuous row
02Two
Dimensional
Two Dimensional or 2-D
array is a type of
matrix in which
elements are stored in
rows and columns
03Multi
Dimensional
Multi Dimensional
array is a type of
nested array

Working With Arrays – 1D
arrayRefVar = new dataType[arraySize];
=myArray new int[5]
Declaring and Initializing an One Dimensional Array
datatype[] arrayRefVar = new dataType[arraySize];
=int[5] myArray new int[5]

myArray
myArray[0] myArray[1] myArray[2] myArray[3] myArray[4]
=myArray[0] 10

myArray
=myArray[2]
10
30
=myArray[3] 40
=myArray[4] 50
=myArray[1] 20

myArray
10 30 40 5020

10 30 40 5020
dataType[] arrayRefVar = new dataType{e1,e2,e3,…,eN};
=int[] myArray new int{10,20,30,40,50}

10 30 40 5020
int[] myArray
dataType[] arrayRefVar = new dataType{e1,e2,e3,…,eN};

Accessing a specific array element
myArray[0]
myArray[1]
myArray[2]
myArray[3]
myArray[4]
10
30
40
50
20
arrayRefVar[index]
myArray[4]
myArray[1]

100
myArray[0]
myArray[1]
myArray[2]
myArray[3]
myArray[4]
10
30
40
50
20
arrayRefVar[index]
myArray[4]
myArray[1]
Updating a specific array element
arrayRefVar[index] = newValue
myArray[4] = 100

myArray[4] = 100
myArray[0]
myArray[1]
myArray[2]
myArray[3]
myArray[4]
10
30
50
20
arrayRefVar[index]
myArray[4]
myArray[1]
arrayRefVar[index] = newValue
100

Declaring and Initializing an Two Dimensional Array
datatype[][] arrayRefVar = new dataType[row][col];
=int[][] myArray new int[2][2]
myArray[0][0] myArray[0][1]
=myArray[0][0] 100

=myArray[0][1] 200
100 =myArray[1][0] 300
=myArray[1][1] 400

100 200
300 400

564
arrayRefVar[row][col]
100 200
300 400
myArray[0][1]
arrayRefVar[row][col] = newValue
myArray[0][1] = 564

myArray[0][1] = 564
arrayRefVar[row][col]
100
300 400
myArray[0][1]
arrayRefVar[row][col] = newValue
564

Operations With Arrays
1 2 3
6
987
4 5
1 2 1
3
271
5 4
Addition of Matrices
a[3][3] b[3][3]

1 2 3
6
987
4 5
1 2 1
3
271
5 4
2 4 4
9
11158
9 9
a[3][3]
b[3][3]
c[3][3]
int[][] c = new int[rows][columns];
for (int i = 0; i < rows; i++)
{
for (int j = 0; j < columns; j++)
{
c[i][j] = a[i][j] + b[i][j];
}
}

1 2 3
6
987
4 5
1 2 1
3
271
5 4
Division
a[3][3] b[3][3]
Multiplication
Subtraction

Sorting in Array
Java offers various sorting algorithms that helps in putting elements of a list in a certain order
Bubble Sort Insertion Sort Merge Sort
Quick SortSelection Sort
Types of Sorting Algorithms

Merge SortQuick SortInsertion SortSelection SortBubble Sort
4 1 10 -3 12
4 1 10 -3 12
1 4 10 -3 12
1 4 10 -3 12
1 4 -3 10 12
1 4 -3 10 12
1 -3 4 10 12
1 -3 4 10 12
1 -3 4 10 12
-3 1 4 10 12
-3 1 4 10 12
void bubbleSort(int arr[])
{
int n = arr.length;
for (int i = 0; i < n-1; i++)
for (int j = 0; j < n-i-1; j++)
if (arr[j] > arr[j+1])
{
// swap temp and arr[i]
int temp = arr[j];
arr[j] = arr[j+1];
arr[j+1] = temp;
}
}

4 1 10 -3 12
4 1 10 -3 12
-3 1 10 4 12
-3 1 10 4 12
-3 1 4 10 12
void selectionSort(int arr[])
{
int n = arr.length;
// One by one move boundary of unsorted subarray
for (int i = 0; i < n-1; i++)
{
// Find the minimum element in unsorted array
int min_idx = i;
for (int j = i+1; j < n; j++)
if (arr[j] < arr[min_idx])
min_idx = j;
// Swap the found minimum element with the first element
int temp = arr[min_idx];
arr[min_idx] = arr[i];
arr[i] = temp;
}
}

4 1 10 -3 12
4 1 10 -3 12
1 4 10 -3 12
1 4 10 -3 12
-3 1 4 10 12
public static int[] insertionSort(int[] input){
int temp;
for (int i = 1; i < input.length; i++) {
for(int j = i ; j > 0 ; j--){
if(input[j] < input[j-1]){
// Swap with the smallest value
temp = input[j];
input[j] = input[j-1];
input[j-1] = temp;
}
}
}
return input;
}
-3 1 4 10 12

2 6 7 4 1 -2 8 4 3
2 6 7 4 1 -2 8 4 3
2 7 3 1 -2 8 4 46
2 1 6 7 -2 8 4 43
2 1 -2 4 6 8 7 43
2 1 -2 4 4 8 7 63
private void quickSort(int low, int high) {
int i = low;
int j = high;
// pivot is middle index
int pivot = input[low + (high - low) / 2];
// Divide into two arrays
while (i <= j) {
while (input[i] < pivot) {
i++;
}
while (input[j] > pivot) {
j--;
}
if (i <= j) {
swap(i, j);
// move index to next position on both sides
i++;
j--;
}
}

2 6 7 4 1 -2 8 4 3
2 6 7 4 1 -2 8 4 3
2 7 3 1 -2 8 4 46
2 1 6 7 -2 8 4 43
2 1 -2 4 6 8 7 43
2 1 -2 4 4 8 7 63
swap(i, j);
// move index to next position on both sides
i++;
j--;
}
}
// calls quickSort() method recursively
if (low < j) {
quickSort(low, j);
}
if (i < high) {
quickSort(i, high);
}
}
private void swap(int i, int j) {
int temp = input[i];
input[i] = input[j];
input[j] = temp;
}
}

4 1 10 -3 12
4 1 10 -3 12
4 1 10 -3 12
4 1 10 -3 12
1 4 10 -3 12
1 4 10 -3 12
-3 1 4 10 12
// Merges two subarrays of arr[]
// First subarray is arr[l..m]
// Second subarray is arr[m+1..r]
void mergeSort(int arr[], int l, int m, int r)
{
// Find sizes of two subarrays to be merged
int n1 = m - l + 1;
int n2 = r - m;
/* Create temp arrays */
int L[] = new int [n1];
int R[] = new int [n2];
/*Copy data to temp arrays*/
for (int i=0; i<n1; ++i)
L[i] = arr[l + i];
for (int j=0; j<n2; ++j)
R[j] = arr[m + 1+ j];

4 1 10 -3 12
4 1 10 -3 12
4 1 10 -3 12
1 4 10 -3 12
1 4 10 -3 12
-3 1 4 10 12
/* Merge the temp arrays */
// Initial indexes of first and second subarrays
int i = 0, j = 0;
// Initial index of merged subarry array
int k = l;
while (i < n1 && j < n2)
{
if (L[i] <= R[j])
{
arr[k] = L[i];
i++;
}
else
{
arr[k] = R[j];
j++;
}
k++;
}
for (int i=0; i<n1; ++i)
L[i] = arr[l + i];
for (int j=0; j<n2; ++j)
R[j] = arr[m + 1+ j];
4 1 10 -3 12

4 1 10 -3 12
4 1 10 -3 12
4 1 10 -3 12
4 1 10 -3 12
1 4 10 -3 12
1 4 10 -3 12
-3 1 4 10 12
/* Copy remaining elements of L[] if any */
while (i < n1)
{
arr[k] = L[i];
i++;
k++;
}
/* Copy remaining elements of R[] if any */
while (j < n2)
{
arr[k] = R[j];
j++;
k++;
}
}
k++;
}

4 1 10 -3 12
4 1 10 -3 12
4 1 10 -3 12
4 1 10 -3 12
1 4 10 -3 12
1 4 10 -3 12
-3 1 4 10 12
k++;
}
}
// Main function that sorts arr[l..r] using
// merge()
void sort(int arr[], int l, int r)
{
if (l < r)
{
// Find the middle point
int m = (l+r)/2;
// Sort first and second halves
sort(arr, l, m);
sort(arr , m+1, r);
// Merge the sorted halves
merge(arr, l, m, r);
}
}

Sorting in Array
Java offers various sorting algorithms that helps in putting elements of a list in a certain order
Types of Searching Algorithms
Binary SearchLinear Search

4
1
10
-3
12
static int search(int arr[], int n, int x)
{
for (int i = 0; i < n; i++)
{
// Return the index of the element if the
element
// is found
if (arr[i] == x)
return i;
}
// return -1 if the element is not found
return -1;
}

2 6 7 9 15 26 50 79 83
2 6 7 9 15 26 50 79 83
15 26 50 79 83
int binarySearch(int arr[], int l, int r, int x)
{
if (r>=l)
{
int mid = l + (r - l)/2;
// If the element is present at the
// middle itself
if (arr[mid] == x)
return mid;
// If element is smaller than mid, then
// it can only be present in left subarray
if (arr[mid] > x)
return binarySearch(arr, l, mid-1, x);
// Else the element can only be present
// in right subarray
return binarySearch(arr, mid+1, r, x);
}

Arrays in Java | Edureka

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