Java Arrays
Java Arrays
Arrays are used to store multiple values in a single variable, instead of declaring separate variables for each value.
To declare an array, define the variable type with square brackets [ ] :
String[] cars;
We have now declared a variable that holds an array of strings. To insert
values to it, you can place the values in a
comma-separated list, inside curly braces { }:
String[] cars = {"Volvo", "BMW", "Ford", "Mazda"};
To create an array of integers, you could write:
int[] myNum = {10, 20, 30, 40};
Access the Elements of an Array
You can access an array element by referring to the index number.
This statement accesses the value of the first element in cars:
Example
String[] cars = {"Volvo", "BMW", "Ford", "Mazda"};
System.out.println(cars[0]);
// Outputs Volvo
Note: Array indexes start with 0: [0] is the first element. [1] is the second element, etc.
Think of an array as numbered boxes, where each box stores an element:
| Index | Element |
|---|---|
| 0 | Volvo |
| 1 | BMW |
| 2 | Ford |
| 3 | Mazda |
Change an Array Element
To change the value of a specific element, refer to the index number:
Example
cars[0] = "Opel";
Example
String[] cars = {"Volvo", "BMW", "Ford", "Mazda"};
cars[0] = "Opel";
System.out.println(cars[0]);
// Now outputs Opel instead of Volvo
Array Length
To find out how many elements an array has, use the length property:
Example
String[] cars = {"Volvo", "BMW", "Ford", "Mazda"};
System.out.println(cars.length);
// Outputs 4
The new Keyword
You can also create an array by specifying its size with new.
This makes an empty array with space for a fixed number of elements, which you can fill later:
Example
String[] cars = new String[4]; // size is 4
cars[0] = "Volvo";
cars[1] = "BMW";
cars[2] = "Ford";
cars[3] = "Mazda";
System.out.println(cars[0]); // Outputs Volvo
However, if you already know the values, you don't need to write new.
Both of these create the same array:
Example
// With new
String[] cars = new String[] {"Volvo", "BMW", "Ford", "Mazda"};
// Shortcut (most common)
String[] cars = {"Volvo", "BMW", "Ford", "Mazda"};
Note: You cannot write new String[4] {"Volvo", "BMW", "Ford", "Mazda"}.
In Java, when using new, you either:
- Use
new String[4]to create an empty array with 4 slots, and then fill them later - Or use
new String[] {"Volvo", "BMW", "Ford", "Mazda"}(without specifying the number of elements) to create the array and assign values at the same time
Tip: The shortcut syntax is most often used when the values are known at the start.
Use new with a size when you want to create an empty array and fill it later.
