Java – Arrays Basics

In this tutorial, you’ll learn about Arrays in Java and how you can use the one dimensional arrays and two dimensional arrays in your Java applications.

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Introduction of Arrays in Java

An array in Java is a collection of similar types of elements with a contiguous memory location. In an array, we can store the same data structure elements. Java array inherits the Object class and implements the Serializable as well as Clone-able interfaces. We can store primitive values or objects in an array in Java. Java supports single and multidimensional arrays.

Let’s see them in detail.

Array Indices

Indexing an array starts with 0: [0], which is the first element. Elements in an array of N integers can be searched using

• Binary search
• Linear search
• Guava
• Stream api
• Using array list
• Using recursion

One Dimensional Array

One dimensional array contains one row and one column of element of same data structure which makes it linear in structure.

Syntax for one-dimensional arrays

The general form of a one-dimensional array declaration is

type var-name[];
OR
type[] var-name;

In this syntax , type declares the element type of the array.

Example of 1D Array

Input

public class Main{  
public static void main(String args[]){  
    int a[]=new int[5];  
    a[0]=111; 
    a[1]=112;  
    a[2]=113;  
    a[3]=114;  
    a[4]=115;  
    for(int i=1;i<a.length;i++)  
    System.out.println(a[i]);  
}} 

Output

112
113
114
115

Array Literal

The null literal is used to represent the absence of an object, and can also be used to represent the absence of an array. For example:

String [] name = null;

If you know the size and variables of array, array literals can be used.

Accessing Array Elements using For Loop

The elements in the array can be accessed through the following methods.

Using for loop

You can use a “for loop” to access the array element. While using the ‘for loop’ a counter variable accesses each element of the array.

Sample program using for loop to access the elements of an array

import java.io.*; 
public class Main { 
      public static void main(String args[]) throws IOException 
        { 
            int ar[] = { 111, 112, 113, 114, 115, 116, 117, 118 }; 
            int i, a; 
            for (i = 0; i < ar.length;i++)
            { 
                a = ar[i]; 
                System.out.print(a + " "); 
            } 
        } 
} 

Output:

111 112 113 114 115 116 117 118

Using for each loop

‘For each’ is a traversing technique, were this loop optimizes the code, save typing and time.

Here we declare a variable that is the same type as the base type of the array, followed by a colon, which is then followed by the array name.

Sample program using for each to access the elements in an array.

import java.io.*; 
public class Main { 
      public static void main(String args[]) throws IOException 
    { 
        int ar[] = { 111, 112, 113, 114, 115,}; 
        int a; 
          for (int i : ar) { 
           a = i; 
            System.out.print(a + " "); 
        } 
    } 
}  

Output:

111 112 113 114 115

Array of Objects

An array is a collection of the same data type that dynamically creates objects. Java allows us to store objects in an array. In Java, the class is also a user-defined data type. An array that conations class type elements are known as an array of objects. Here, it stores the reference variable of the object.

Creating an Array of Objects

You can use any of the following statements to create an array of objects.

Syntax:

ClassName obj[]=new ClassName[array_length]; 
Or
ClassName[] objArray;  
Or
ClassName objeArray[];  

Sample program for creating an array of objects

public class Main  
{  
    public static void main(String args[])  
    {  
        Product[] obj = new Product[5] ;  
        obj[0] = new Product(11111,"Samsung");  
        obj[1] = new Product(22222,"Apple");  
        obj[2] = new Product(33333,"Vivo");  
        obj[3] = new Product(44444,"Oppo ");  
        obj[4] = new Product(43590,"Huawei ");  
        System.out.println("Product Object 1:");  
        obj[0].display();  
        System.out.println("Product Object 2:");  
        obj[1].display();  
        System.out.println("Product Object 3:");  
        obj[2].display();  
        System.out.println("Product Object 4:");  
        obj[3].display();  
        System.out.println("Product Object 5:");  
        obj[4].display();  
    }  
    
}  
class Product  
{  
    int pro_Id;  
    String pro_name;  
    Product(int pid, String n)  
    {  
    pro_Id = pid;  
    pro_name = n;  
    }  
    public void display()  
    {  
    System.out.print("Product Id = "+pro_Id + "  " + " Product Name = "+pro_name);  
    System.out.println();  
    }  
}

Output:

Product Object 1:
Product Id = 11111   Product Name = Samsung
Product Object 2:
Product Id = 22222   Product Name = Apple
Product Object 3:
Product Id = 33333   Product Name = Vivo
Product Object 4:
Product Id = 44444   Product Name = Oppo
Product Object 5:
Product Id = 55555  Product Name = Huawei

Java Multidimensional Arrays

A multidimensional array is an array of arrays. Each element of a multidimensional array is an array itself. Java supports 2-dimensional and 3-dimensional arrays. Let us see the 2D arrays in detail.

2-dimensional array in Java

The 2D array is a collection of rows and columns.  These arrays are created to implement a relational database look like data structure. Holding bulk data at once and its related functions can be handled easily using 2D array.

How to initialize a 2d array in Java?

Here is how we can initialize a 2-dimensional array in Java.

Initialization – Syntax:

array_name[row_index][column_index] = value;
        For example: arr[0][0] = 1;
       

Sample program for using 2D arrays in Java

class Main {
    public static void main(String[] args) {
        int[][] a = {
            {111, 112, 113}, 
            {114, 115, 116, 119}, 
            {117}, 
        };
        System.out.println("Length of row 1: " + a[0].length);
        System.out.println("Length of row 2: " + a[1].length);
        System.out.println("Length of row 3: " + a[2].length);
    }
}

Output:

Length of row 1: 3
Length of row 2: 4
Length of row 3: 1

Jagged Array in Java

What is Jagged Array?

Jagged array is a type of  multidimensional array where the member arrays are of different size i.e., we can create a 2-D array but with a variable number of columns in each row. These types of arrays are also known as jagged arrays.

Declaration and Initialization of Jagged array:

Syntax

data_type array_name[][] = new data_type[n][];  
array_name[] = new data_type[n1]
             array_name[] = new data_type[n2] 
             array_name[] = new data_type[n3] 
                                   .	
  .
  .
  array_name[] = new data_type[nk] 

Arrays and Exceptions

1. NullPointerException -In Java a NullPointerException is a class which also extends RuntimeException. There are the following conditions where the NullPointerException is generated.

• Calling the instance method of a null object.
• Accessing or modifying the field of a null object.
• Taking the length of null as if it were an array.
• Accessing or modifying the slots of null as if it were an array.
• Throwing null as if it were a Throwable value.

 2. NegativeArraySizeException -This error is when you wants create an array with a negative size.

 NegativeArraySizeException is a class in Java which extends RuntimeException.

 3. ArrayIndexOutOfBoundsException – This type of error is generated when an array has been accessed with an illegal index.

 4. IndexOutOfBoundsException – This type of exception is by all indexing pattern data types such as an array string and a vector etc. when it is accessed out of the index (range). IndexOutOfBoundException is also a separate class in Java and it extends RuntimeException.

 5. ClassCastException – The ClassCastException is thrown when the following code has attempted to cast an object to a subclass of which it is not an instance.

6. ArrayStoreException – This type of exception is to indicate that an attempt has been made to store the wrong type of object into an array of objects. 

How to Pass Arrays to Methods?

You can pass arrays to a method just like normal variables. When you pass an array to a method as an argument, so basically the address of the array in the memory is passed. Therefore, any changes to this array in the method will affect the array.

Example

Input

import java.util.Scanner;
public class Main {
   public static int x(int [] array) {
      int x = 0;
      for(int i=0; i<array.length; i++ ) {
         if(array[i]>x) {
            x = array[i];
         }
      }
      return x;
   }
   public static int y(int [] array) {
      int y = array[0];
      for(int i = 0; i<array.length; i++ ) {
         if(array[i]<y) {
            y = array[i];
         }
      }
      return y;
   }
   public static void main(String args[]) {
      Scanner sc = new Scanner(System.in);
      System.out.println("Enter the size of the array that is to be created::");
      int size = sc.nextInt();
      int[] myArray = new int[size];
      System.out.println("Enter the elements of the array ::");
      for(int i=0; i<size; i++) {
         myArray[i] = sc.nextInt();
      }
      System.out.println("Maximum value in the array is::"+x(myArray));
      System.out.println("Minimum value in the array is::"+y(myArray));
   }
}

Output

Enter the size of the array that is to be created:
5
Enter the elements of the array ::
111
112
113
114
115
Maximum value in the array is: 115
Minimum value in the array is: 111

How to Return Arrays from Methods in Java?

We can return an array in Java from a method in Java. Here we have a method createArray() from which we create an array dynamically by taking values from the user and return the created array.

Input

import java.util.Arrays;
import java.util.Scanner;
public class Main {
   public static int[] createArray() {
      Scanner sc = new Scanner(System.in);
      System.out.println("Enter the size of the array that is to be created:: ");
      int size = sc.nextInt();
      int[] myArray = new int[size];
      System.out.println("Enter the elements of the array ::");
      for(int i=0; i<size; i++) {
         myArray[i] = sc.nextInt();
      }
      return myArray;
   }
   public static void main(String args[]) {
      int arr[] = createArray();
      System.out.println("Array created is :: "+Arrays.toString(arr));
   }
}

Output

Enter the size of the array that is to be created::
5
Enter the elements of the array ::
111
112
113
114
115
Array created is :: [111, 112, 113, 114, 115]

How to Clone Arrays in Java?

Clone methods create a new array of the same size. Let’s see how to clone a array through a program.

Sample program for cloning an array in Java

Input

public class Main {
    public static void main(String[] args)
    {
        int a[] = { 111, 112, 113 };
         int b[] = a.clone();
         b[0]++;
         System.out.println("Contents of a[] ");
        for (int i = 0; i < a.length; i++)
            System.out.print(a[i] + " ");
         System.out.println("\n\nContents of b[] ");
        for (int i = 0; i < b.length; i++)
            System.out.print(b[i] + " ");
    }
}

Output

Contents of a[] 
111 112 113 
Contents of b[] 
111 112 113