Learn Java – Arrays

Java – Arrays

Learn Java – Arrays

Java provides a data structure, the array, which stores a fixed-size sequential collection of elements of the same type. An array is used to store a collection of data, but it is often more useful to think of an array as a collection of variables of the same type.

Instead of declaring individual variables, such as number0, number1, …, and number99, you declare one array variable such as numbers and use numbers[0], numbers[1], and …, numbers[99] to represent individual variables.

This tutorial introduces how to declare array variables, create arrays, and process arrays using indexed variables.

Declaring Array Variables:

To use an array in a program, you must declare a variable to reference the array, and you must specify the type of array the variable can reference. Here is the syntax for declaring an array variable:

dataType[] arrayRefVar;   // preferred way.


dataType arrayRefVar[];  //  works but not preferred way.

Note: The style dataType[] arrayRefVar is preferred. The style dataType arrayRefVar[] comes from the C/C++ language and was adopted in Java to accommodate C/C++ programmers.


The following code snippets are examples of this syntax:

double[] myList;         // preferred way.


double myList[];         //  works but not preferred way.

Creating Arrays:

You can create an array by using the new operator with the following syntax:

arrayRefVar = new dataType[arraySize];

The above statement does two things:

  • It creates an array using new dataType[arraySize];
  • It assigns the reference of the newly created array to the variable arrayRefVar.

Declaring an array variable, creating an array, and assigning the reference of the array to the variable can be combined in one statement, as shown below:

dataType[] arrayRefVar = new dataType[arraySize];

Alternatively you can create arrays as follows:

dataType[] arrayRefVar = {value0, value1, ..., valuek};

The array elements are accessed through the index. Array indices are 0-based; that is, they start from 0 to arrayRefVar.length-1.


Following statement declares an array variable, myList, creates an array of 10 elements of double type and assigns its reference to myList:

double[] myList = new double[10];

Following picture represents array myList. Here, myList holds ten double values and the indices are from 0 to 9.

Java Array

Processing Arrays:

When processing array elements, we often use either for loop or foreach loop because all of the elements in an array are of the same type and the size of the array is known.


Here is a complete example of showing how to create, initialize and process arrays:

public class TestArray {

   public static void main(String[] args) {
      double[] myList = {1.9, 2.9, 3.4, 3.5};

      // Print all the array elements
      for (int i = 0; i < myList.length; i++) {
         System.out.println(myList[i] + " ");
      // Summing all elements
      double total = 0;
      for (int i = 0; i < myList.length; i++) {
         total += myList[i];
      System.out.println("Total is " + total);
      // Finding the largest element
      double max = myList[0];
      for (int i = 1; i < myList.length; i++) {
         if (myList[i] > max) max = myList[i];
      System.out.println("Max is " + max);

This would produce the following result:

Total is 11.7
ax is 3.5

The foreach Loops:

JDK 1.5 introduced a new for loop known as foreach loop or enhanced for loop, which enables you to traverse the complete array sequentially without using an index variable.


The following code displays all the elements in the array myList:

public class TestArray {

   public static void main(String[] args) {
      double[] myList = {1.9, 2.9, 3.4, 3.5};

      // Print all the array elements
      for (double element: myList) {

This would produce the following result:


Passing Arrays to Methods:

Just as you can pass primitive type values to methods, you can also pass arrays to methods. For example, the following method displays the elements in an int array:

public static void printArray(int[] array) {
  for (int i = 0; i < array.length; i++) {
    System.out.print(array[i] + " ");

You can invoke it by passing an array. For example, the following statement invokes the printArray method to display 3, 1, 2, 6, 4, and 2:

printArray(new int[]{3, 1, 2, 6, 4, 2});

Returning an Array from a Method:

A method may also return an array. For example, the method shown below returns an array that is the reversal of another array:

public static int[] reverse(int[] list) {
  int[] result = new int[list.length];

  for (int i = 0, j = result.length - 1; i < list.length; i++, j--) {
    result[j] = list[i];
  return result;

The Arrays Class:

The java.util.Arrays class contains various static methods for sorting and searching arrays, comparing arrays, and filling array elements. These methods are overloaded for all primitive types.

SN Methods with Description
1 public static int binarySearch(Object[] a, Object key)Searches the specified array of Object ( Byte, Int , double, etc.) for the specified value using the binary search algorithm. The array must be sorted prior to making this call. This returns index of the search key, if it is contained in the list; otherwise, (-(insertion point + 1).
2 public static boolean equals(long[] a, long[] a2)Returns true if the two specified arrays of longs are equal to one another. Two arrays are considered equal if both arrays contain the same number of elements, and all corresponding pairs of elements in the two arrays are equal. This returns true if the two arrays are equal. Same method could be used by all other primitive data types (Byte, short, Int, etc.)
3 public static void fill(int[] a, int val)Assigns the specified int value to each element of the specified array of ints. Same method could be used by all other primitive data types (Byte, short, Int etc.)
4 public static void sort(Object[] a)Sorts the specified array of objects into ascending order, according to the natural ordering of its elements. Same method could be used by all other primitive data types ( Byte, short, Int, etc.)


Gencor Learning Solutions (P) Ltd.

Road 3, Rajendra Nagar,

Patna, Bihar, India 


Ph: +91 9304302624

       +91 612 3226111


    Contact us for Training & Certification



    Mobile Number


    Mode of Training

    By sending your details you agree to our terms and conditions*

    I am happy to be here in Gencor which provided me with technical professional and skillful aspects of auto cad, thank you.

    Kush Prakash - West Bengal University of Technology

    I completed CCNA traning and certification preparation before appearing for ccna global examination 200-120 from gencor.

    Amit Kumar - Lovely Professional University

    The trainer has good knowledge of the subject.

    Saurabh Kumar Suman - Shaheed Bhagat Singh State Technical Campus, Ferozepur

    This institute is the best institute in web designing. Trainer sir is good in knowledge and best trained and  provided web designing knowledge to me.

    Abhishek Kumar - Guru Gobind Singh Polytechnic College, Talwandi Sabo, (Bhathinda) Punjab

    The trainer is good, so I think everything is good. 

    Rabindra Kumar Yadav - Samalkha Group of Institutions

    The Gencor classes is good for getting the knowledge. The trainer has good communication with students. I completed CAD training in Mechanical from here.

    Akash Kumar - Jawaharlal Nehru Technological University, Hyderabad

    I gained a lot here in the Gencor and I believe that it will help to enhance my knowledge and personalty further in my life.

    Prem Kumar - BIT Sindri

    Institute Completed my training as per  Syllabus provided on time. 

    Akshay Kumar - The Institution of Civil Engineers, Delhi

    Gencor institute is the best institute which completed my course on Civil CAD on time.

    Amit Kumar - Reg No - 001/15348 - Civil CAD

    The overall system of teaching is favorable and good as I expected and helped a lot in increasing my knowledge.

    Sunny Kumar

    I appreciate the course by the institute and efforts put in to complete it within the prescribed time limits.

    Mohammad Asad Eqbal

    The trainer has good knowledge of autocad, so I am happy to complete the training of AutoCAD from here.

    Hemant Raj - Reg No.: 001/15307 - Civil CAD

    The Trainer is nice one. He teaches well. The institute is good. I have faith on the Institute.

    Vikash Kr Mandal - Reg No.: 001/15308 - Mechanical CAD

    The institute is very good one and object oriented, focused on setting  up career for engineering students. The trainer is having enough knowledge to guide students.Teaching method is very much appreciated and interactive.

    Indranil Mazumdar - Reg No.: 001/15312 - Civil CAD

    All class I did here was very good. Faculty provide every detail about syllabus & Course. I am thankful of you.

    Sumank Saurav - Reg No.: 001/15321 - Mechanical CAD

    Trainer is the best guide for autocad and institute is also best for autocad

    Vikash Kumar Sharma - Reg No.: 001/15322 - Mechanical CAD

    This is professional institute , It has given the full knowledge of the subject, It is best best providing knowledge.

    Dinu Kumar - Reg No.: 001/15328 - AutoCAD ME

    This institute given me knowledge about Autocad and I appreciate that . I must recommend other to learn CAD from here.  

    Abhishek Kr Singh (Reg No . 001/15332)

    I am Gracy Pradhan , completed my  Linux training on RHCE from GenCor. Training is fully practical based and full syllabus coverage prescribed RED Hat Inc. . This training is surely going to provide me help in placement by college.

    Gracy Pradhan - Ram Krishna Dharmarth Foundation University

    I completed my Autocad Civil Training with Project and certification from GenCor InfoEdge – India, Trainer is The best in providing training .

    Sonu Kumar

    Best Training for telecommunication on Cisco CCNA. I got placed in 3i infotech Patna.

    Scan the code