Arrays in Java

Arrays in Java

Array is a container that holds objects that are of similar type.Array length is determined during it creation.Below diagram shows an array of ten objects.

Example of Array in Java 

public class ArrayExample {
    
    public static void main(String args[])
    {
    int [] arrayNumbers;
    arrayNumbers=new int[6];
    arrayNumbers[0]=100;
    arrayNumbers[1]=700;
    arrayNumbers[2]=200;
    arrayNumbers[3]=800;
    arrayNumbers[4]=600;
    arrayNumbers[5]=400;
    
      System.out.println("Element at index 0: "
                           +   arrayNumbers[0]);
    System.out.println("Element at index 1: "
                           +   arrayNumbers[1]);
    System.out.println("Element at index 2: "
                           +   arrayNumbers[2]);
    System.out.println("Element at index 3: "
                           +   arrayNumbers[3]);
    System.out.println("Element at index 4: "
                           +   arrayNumbers[4]);
    
    System.out.println("Element at index 5: "
                           +   arrayNumbers[5]);
    }
    
    
}

Declaring other types of array

Just like other variables array declaration has two components i.e

Array Datatype

Array Name

Array naming should follow naming conventions we discussed earlier.

NB:Array declaration does not create actually array but notifies compiler this variable will hold array data type.Below are other types of array declaration.

byte[] arrayOfBytes; 
short[] 
arrayOfShorts; 
long[] arrayOfLongs; 
float[] arrayOfFloats; 
double[] arrayOfDoubles; 
boolean[] arrayOfBooleans; 
char[] arrayOfChars; 
String[] arrayOfStrings;

Also putting the brackets at the end of array variable name is allowed

i.e int arrayNumbers[] 

  however this is discouraged.

Array creation, Initializing and Accessing it

One way to create array is to use new keyword .eg  

int [] arrayNumbers=new Array[5];

Assigning elements in an array can be done as show below.

    arrayNumbers[0]=100;    arrayNumbers[1]=700;    arrayNumbers[2]=200;    arrayNumbers[3]=800;    arrayNumbers[4]=600;    arrayNumbers[5]=400;

Elements in the array can then be accessed by using their index.

      System.out.println("Element at index 0: "                           +   arrayNumbers[0]);    System.out.println("Element at index 1: "                           +   arrayNumbers[1]);    System.out.println("Element at index 2: "                           +   arrayNumbers[2]);    System.out.println("Element at index 3: "

Alternatively,many programmers consider creating and initializing array at the same time.

int arrayNumbers[]={200,300,400,500,600,700}; 

Creating a multidimensional array  in Java

multidimensional arrays are also known as an array of arrays.They are created using two or more brackets [] [].

Example

public class MultiArrayExample {
    public static void main(String args[])
    {
    
     String[][] marks = {
            {"John ", "Eric ", "Jessica "},
            {"40", "70","80"}
        };
        // Mr. Smith
        System.out.println(marks[0][0] + marks[1][0]);
        // Ms. Jones
        System.out.println(marks[0][1] + marks[1][1]);
         System.out.println(marks[0][2] + marks[1][2]);
         
         System.out.println("Array length is " +marks.length );
    }
    
}

Output

John 40Eric 70Jessica 80

Array length can be determined by

       

         System.out.println("Array length is " +marks.length );

Using arraycopy method 

the arraycopy method can be used to copy  data from one array into another.

Example

public class ArrayCopyMethodExample {
    
    public static void main(String args[])
    {
    char copyFrom[]={'d','r','e','r','i','c','p','f'};
    char[] copyTo = new char[4];
    
       System.arraycopy(copyFrom, 2, copyTo, 0, 4);
         System.out.println(new String(copyTo));
    }
}

Output

run:

eric

BUILD SUCCESSFUL (total time: 0 seconds)