arraylist in java | array in java example

Array in Java

 

Java array is an object which contains elements of a similar data type. Additionally, The elements of an array are stored in a contiguous memory location. It is a data structure where we store similar elements. We can store only a fixed set of elements in a Java array.

Array in Java is index-based, the first element of the array is stored at the 0th index, 2nd element is stored on 1st index and so on.

Unlike C/C++, we can get the length of the array using the length member. In C/C++, we need to use the sizeof operator.

In Java, array is an object of a dynamically generated class. Java array inherits the Object class, and implements the Serializable as well as Cloneable interfaces. We can store primitive values or objects in an array in Java. Like C/C++, we can also create single dimentional or multidimentional arrays in Java.

Moreover, Java provides the feature of anonymous arrays which is not available in C/C++.

 

array indexing

Advantages and Disadvantage of Array and they are

Advantages

• Code Optimization: It makes the code optimized, we can retrieve or sort the data efficiently.

• Random access: We can get any data located at an index position.

Disadvantages

• Size Limit: We can store only the fixed size of elements in the array. It doesn't grow its size at runtime. To solve this problem, collection framework is used in Java which grows automatically.

How can we declare array in java?

Here's how you can declare an array in Java:

          Datatype[] arrayname;

·         dataType can be a primitive data type like: int, char, Double, byte etc.   or an object (will be discussed in later chapters).

·         arrayName is an identifier.

Example

double [] data

But, how many elements can array this hold?

Good question! We haven't defined it yet. The next step is to allocate memory for array elements.

data= new Double[10];

The length of data array is 10. Meaning, it can hold 10 elements (10 Double values in this case).

Note, once the length of the array is defined, it cannot be changed in the program.

Java Array Index 

You can access elements of an array by using indices.Example

int[] age=new age[5];

array in java

The first element of array is age[0], second is age[1] and so on.

If the length of an array is n, the last element will be arrayName[n-1]. Since the length of age array is 5, the last element of the array is age[4] in the above example.

The default initial value of elements of an array is 0 for numeric types and false for boolean.

Example:

class ArrayExam

{

public static void main(String agrs[])  {

int[] age=new age[5];

for(int i=0;i<5;i++)

System.out.println(age[i]);

}}

How to initialize arrays in Java?

In Java, you can initialize arrays during declaration or you can initialize (or change values) later in the program as per your requirement.

Initialize an Array During Declaration

int[] age={12,4,5,2,5};

This statement creates an array and initializes it during declaration.

The length of the array is determined by the number of values provided which is separated by commas. In our example, the length of age array is 5.

 

java array

Simple program in java

class ArrayExam

{

public static void main(String agrs[])  {

int[] age={12,4,5,2,5};

for(int i=0;i<5;i++)

{

System.out.println(age[i]);

}

}

}

Output:

12

4

5

3

5

Types of Array in java

There are two types of array.

• Single Dimensional Array
• Multidimensional Array

Single Dimensional Array in Java

Syntax to Declare an Array in Java

dataType[] arr; (or)  

dataType arr[];  

Example

     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;  

//traversing array  

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

System.out.println(a[i]);  

}}  

Output

10

20

70

40

50

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:

//Java Program to illustrate the use of multidimensional array  

class Testarray3{  

public static void main(String args[]){  

//declaring and initializing 2D array  

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

//printing 2D array  

for(int i=0;i<3;i++){  

 for(int j=0;j<3;j++){  

   System.out.print(arr[i][j]+" ");  

 }  

 System.out.println();  

}  

}}  

Output:

123

245

445

Jagged Array in Java

If we are creating odd number of columns in a 2D array, it is known as a jagged array. In other words, it is an array of arrays with different number of columns.

//Java Program to illustrate the jagged array  

class TestJaggedArray{  

    public static void main(String[] args){  

        //declaring a 2D array with odd columns  

        int arr[][] = new int[3][];  

        arr[0] = new int[3];  

        arr[1] = new int[4];  

        arr[2] = new int[2];  

        //initializing a jagged array  

        int count = 0;  

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

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

                arr[i][j] = count++;  

   

        //printing the data of a jagged array   

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

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

                System.out.print(arr[i][j]+" ");  

            }  

            System.out.println();//new line  

        }  

    }  

}  

Output:

012

3456

78