Java Technology 2018 - Array

Array:
 Array is a collection of similar type of elements that have contiguous memory location. Array in java is index based, first element of the array is stored at 0 index.

Advantage of Java Array

• Code Optimization: It makes the code optimized, we can retrieve or sort the data easily.
• Random access: We can get any data located at any index position.

There are two types of array.

• Single Dimensional Array
• Multidimensional Array

Syntax to Declare an Array in java

dataType[] arr; (or)  

dataType []arr; (or)  

dataType arr[];  

Instantiation of an Array in java

arrayRefVar=new datatype[size];  

class Testarray{  

public static void main(String args[]){  

  

int a[]=new int[5];//declaration and instantiation  

a[0]=10;//initialization  

a[1]=20;  

a[2]=70;  

a[3]=40;  

a[4]=50;  

  

//printing array  

for(int i=0;i<a.length;i++)//length is the property of array  

System.out.println(a[i]);  

  

}}  

int a[]={33,3,4,5};//declaration, instantiation and initialization  

package com.practice;

public class ArrayPractice {

public static void main(String[] args) {

int arr[] = {22,11,44,33};

for(int i:arr){

System.out.println(i);

}

}

}

package com.practice;

public class ArrayFindMinimum {

public static void main(String[] args) {

int arr[] = { 22, 11, 55, 44 };

findMin(arr);

}

public static void findMin(int[] arr) {

int min=arr[0];

       for(int i: arr){

       if(i<min){

       min=i;

       }

       }

       System.out.println(min);

}

}

Multidimensional array in java

In such case, data is stored in row and column based index (also known as matrix form).

Syntax to Declare Multidimensional Array in java

dataType[][] arrayRefVar; (or)  

dataType [][]arrayRefVar; (or)  

dataType arrayRefVar[][]; (or)  

dataType []arrayRefVar[];   

Example to instantiate Multidimensional Array in java

int[][] arr=new int[3][3];//3 row and 3 column 

Java String array: is there a size of method?

Yes, .length (property-like, not a method):

String[] array = new String[10];
int size = array.length;

Getting the array length of a 2D array in Java

If you're treating your 2D array as a matrix, you can simply get z.length and z[0].length, but note that you might be making an assumption that for each array in the 2nd dimension that the length is the same (for some programs this might be a reasonable assumption).

package com.practice;

public class ArrayTwoD {

public static void main(String[] args) {

int arr[][] = { { 1, 2 }, { 44, 3 }, { 8, 5 } };

for (int i = 0; i < arr.length; i++) {

for (int j = 0; j < arr[0].length; j++) {

System.out.print(arr[i][j]+"  ");

}

System.out.println();

}

}

}

int arr1[] = { 0, 1, 2, 3, 4, 5 };

int arr2[] = { 5, 10, 20, 30, 40, 50 };

System.arraycopy(arr1, 0, arr2, 1, 3);

for (int i : arr2) {

System.out.println(i);

}

3 elemens from arr1 index 0 to arr2 index 1 

5

0

1

2

40

50

int arr1[] = { 0, 1, 2, 3, 4, 5 };

int arr2[] = { 5, 10, 20, 30, 40, 50 };

System.arraycopy(arr1, 1, arr2, 1, 3);

for (int i : arr2) {

System.out.println(i);

}

3 elemens from arr1 index 1 to arr2 index 1 

5

1

2

3

40

50