Array In Java

Array

1. Array is a collection of similar type of data.
2. Array is of fixed size. Have to provide size of an array at creation time.
3. Array can store primitive data type and non-primitive.
4. Array itself is a non-primitive data type.
5. To use array, you have to create object of array.
6. Array is always based on index, index always start with 0 and manage by java.
7. There are different types of array for example 1D, 2D, multi-dimensional array.

1-D Array

1. Syntax to create 1-D array
2. Declaration of Array

Data-Type   NameOfArray[];

1. Instance/Object creation of array

NameOfArray = new  Data-Type[size];

1. Initialization of array

NameOfArray[index] = value;

2. Memory allocation of array

3. 4-Ways to create array

1-ways

int marks[]; // declaration of Array.

marks = new int[5]; // Instance of array.

marks[0] = 78; // initialization of array.

marks[1] = 48;

marks[2] = 66;

marks[3] = 74;

marks[4] = 90;

2-ways

int marks[] = new int[5]; // declaration and Instance creation of array.

marks[0] = 78; // initialization of array.

marks[1] = 48;

marks[2] = 66;

marks[3] = 74;

marks[4] = 90;

3-ways

int marks[] = new int[]{78, 48, 66, 74, 90}; //  declaration, instance & initialization

4-ways

int marks[] = {78, 48, 66, 74, 90}; //  declaration, instance & initialization

4. If you try to access an index which is not available then you will end up with following exception

Exception in thread “main” java.lang.ArrayIndexOutOfBoundsException: Index 12 out of bounds for length 12

2-D Array

1. Is use to store data in form of row and column.
2. Syntax
   1. Declaration of array

Data-type   variablename[][];

1. Instance/object creation of array

Variablename = new   Data-type[row-size][column-size];

1. Initialization of array

Variablename[row-index][column-index]  = value;

3. In 2-D array row size is always mandatory and column size is optional.
4. Representation of 2-D arrays

3. There are 4 ways to create 2-d array

1-Way

int marks[][];   // declaration

marks = new int[4][5]; // instance

marks[0][0] = 60; // initialization

marks[0][1] = 90;

marks[0][2] = 88;

marks[0][3] = 70;

marks[0][4] = 51;

2-Way

int marks[][]  =  new int[4][5]; // declaration and instance

marks[0][0] = 60; // initialization

marks[0][1] = 90;

marks[0][2] = 88;

marks[0][3] = 70;

marks[0][4] = 51;

3-Way

int marks[][]  =  new int[][] { {78,56,78,66,56}, {67,87,56,78,49}, {67,78,45,68,89}, {98,86,56,98,67} };

4-Way

int marks[][] = {{78,56,78,66,56}, {67,87,56,78,49}, {67,78,45,68,89}, {98,86,56,98,67}};

6. Use Length in 2-D Array

System.out.println(marks.length); // it will return the total row count

System.out.println(marks[2].length); // it will return the total column count of specified row

Multi-dimensional/ Jagged Array

1. In this type of array rows can have different number of columns.

Using Array to store Custom Class Objects

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