Java Arrays

Java Arrays 

Array is a collection of similar data-types . Also Arrays are used to store multiple values in a single variable, instead of declaring separate variables for each value. 

➤ Declaring an Array

To declare an array, define the variable type with square brackets : 

Syntax :-

  dataType varName [] = { // array elements separated by comma };  

Here I am declaring an array of strings.

  String[] animals;  

As we have declared an array , lets give values to it.

  String[] animals = {"Dog", "Elephant", "Fox", "Cow"};   

➤ Index of an Array

Index of an Array starts from zero.

We also can declare an array of a given size.

Here I declared an array of animals of length 1 i.e It would have 2 containers , 1 at index 0 and other at index 2.

➤ Change an Array element

You can rewrite or replace an array element by declaring it again at the same index.

  public class MyClass {   
    public static void main(String[] args) {   
       String [] animals = new String[1];   
       animals[0]="cat";   
       animals[1]="dog";   
    //changing at index 0      
       animals[0]="hello";   
       System.out.println(animals[0]);   
    }   
  }  

Output:-

 hello  

➤ Array Length

You can find out the length of an array by using the length property.

  public class MyClass {   
    public static void main(String[] args) {   
       String [] animals = {"Cat" , "Dog" , "Elephant"};   
       System.out.println(animals.length);   
    }   
  }  

Output:-

 3  

➤ Using Loops in Array

( If you are not familiar with loops  , check out the JAVA Loops section. )

Any Loops can be used with arrays.

Here we are using for loop :

 public class MyClass {   
    public static void main(String[] args) {   
       String[] animals = { "Cat", "Dog", "Elephant" };   
       for (int i = 0; i < animals.length; i++)    
       {   
         System.out.println(animals[i]);   
       }   
    }   
  }  

Output:-

  Cat   
  Dog   
  Elephant  

➤ Enhanced For Loop (For Each Loop)

Syntax:-

 for (dataType varName : arrayName) {  
 // block of code  
 } 

Flowchart:-

For Each Loop is also called as enhanced for loop.

The overall working is similar , but For Each loop is easier to write and more human readable.

Using For Each Loop in the above program.

 public class MyClass {  
      public static void main(String[] args) {  
           String[] animals = { "Cat", "Dog", "Elephant" };  
           for (String i : animals)  
           {  
                System.out.println(i);  
           }  
      }  
 } 

This will generate the same output as above.

➤ Multi-Dimensional Arrays

Multi-Dimensional Arrays are Arrays within Arrays i.e An Array containing another Array. 

Here we will learn about Two-Dimensional Arrays.

These multi-dimensional arrays can be understood by seeing it as a Matrix.

For 2d arrays it can be understood as a 2x2 Matrix.

Similarly for 3d arrays it will 3x3 Matrix.

Let us consider a 2d array of type int :-

 int [][] myNumbers = { {1,2,3} , {4,5,6} };  

For accessing an element of a particular array:-

 System.out.println(myNumbers[1][2]);  

Here the first [ ] represents the number of array , we chose 1 i.e the 2nd array as its index starts from zero .

And the second [ ] represents the array element in it , we  chose 2 i.e 3rd element as its index starts from zero.

The above code would display result as :-

 6  

As 6 is the 3rd element of 2nd array.

The 3d array works in similar way. You can take help of the following image.

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