Java Array Tutorial

Java provides a data structure called an array, which is a fixed-size ordered collection of elements of the same type. Arrays are used to store collections of data, but arrays can also be thought of as collections of variables of the same type.

Declare an array variable (such as: numbers) and use numbers[0], numbers[1]and ..., numbers[99]to represent a single variable, for example number0, number1, ...and number99, instead of declaring each variable separately.

This tutorial explains how to declare array variables, create arrays and access arrays by index.

1. Declare an array variable

To use an array in a program, you need to declare a variable to refer to the array, and specify the array type of the variable. Following is the syntax for declaring an array variable −

Syntax

dataType[] arrayRefVar;   // Recommended method

dataType arrayRefVar[];  // Works, but not the recommended way.

Note - Format: dataType [] arrayRefVar is the recommended way. Format: dataType arrayRefVar []From C/C++ language, can be adopted in Java to suit C/C++ programmers.

 

Example

The following code snippet is an example of this syntax −

double[] myList;   // Recommended method
double myList[];   // Works, but not the recommended way.

2. How to Create and Initialize Array in Java?

Arrays can be created using new operators as in the following syntax −

dataType[] arrayRefVar; // Create array arrayRefVar = new dataType[arraySize];

The above statement does two things −

• It uses new dataType[arraySize]to create an array.
• It assigns the reference of the newly created array to the variable arrayRefVar.

Declaring an array variable, creating an array, and assigning a reference of that array to the variable can be done in one statement as follows 

Alternatively, an array can be created as follows −

 

Initialize while declaring

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

Access array elements by index. Array index values ​​start from 0start; that is, they go from 0start to arrayRefVar.length - 1.

Example

An array variable is declared in the following statement myList, which creates an array containing elements 10 of double type and assigns a reference to the array variable to myList −

double[] myList = new double[10];

3. Working with arrays

import java.util.*;

public class Test {

    public static void main(String[] args) {
        double[] myList = { 10.01, 12.19, 23.44, 43.95, 77.88, 65.00 };

        
        for (int i = 0; i < myList.length; i++) {
            System.out.print(myList[i] + ", ");
        }
        System.out.println(" ");

       
        double total = 0;
        for (int i = 0; i < myList.length; i++) {
            total += myList[i];
        }
        System.out.println("Sum：" + total);

        
        double max = myList[0];
        for (int i = 1; i < myList.length; i++) {
            if (myList[i] > max)
                max = myList[i];
        }
        System.out.println("Max Element：" + max);
    }
}

Output

10.01, 12.19, 23.44, 43.95, 77.88, 65.0,  
Sum：232.47
Max Element：77.88

3.1. Java Arrays with foreach loop - Iterate Array items with foreach loop

import java.util.*;

public class Test {

    public static void main(String[] args) {
        double[] myList = { 10.01, 12.19, 23.44, 43.95, 77.88, 65.00 };

        // Print all the array elements
        for (double element : myList) {
            System.out.print(element+", ");
        }
    }
}

10.01, 12.19, 23.44, 43.95, 77.88, 65.0,

import java.util.*;

public class Test {

    public static void main(String[] args) {
        double[] myList = { 10.01, 12.19, 23.44, 43.95, 77.88, 65.00 };

        // Print all the array elements
        printArray(myList);
    }

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

Output：

10.01 12.19 23.44 43.95 77.88 65.0

import java.util.*;

public class Test {

    public static void main(String[] args) {
        double[] myList = { 10.01, 12.19, 23.44, 43.95, 77.88, 65.00 };

        // Print all the array elements
        printArray(myList);
        printArray(reverse(myList));
    }

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

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

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

10.01 12.19 23.44 43.95 77.88 65.0  
65.0 77.88 43.95 23.44 12.19 10.01