Arrays
An array is a list of variables, or more succinctly, a list of values. Each value in an array has an index, which is a number that represents the location of the value within the array.
Let’s discuss more about how to create and modify arrays using the following example:
int[] x = new int[] {2, 4, 6, 8, 10, 12};
This stores the numbers 2, 4, 6, 8, and 10 in the array x. The int at the beginning
tells the computer the data type of x, similar to normal variables. The [] tells the computer that x is an array, not a single value.
new int[] tells the computer to create a new array of type int. Then inside the curly brackets we can put our values separated by commas.
Arrays can only be of one type, so you can’t store both Strings and Integers in one array, etc.
Retrieving Values From An Array
Here’s an example of retrieving a specific value from the array above:
int a = x[0]; // 2
int b = x[1]; // 4
int c = x[2]; // 6
int d = x[3]; // 8
int e = x[4]; // 10
The indices of an array start at 0 and increment from left to right. Here is a model of the index-value pairs inside the above array:
| Index | Value |
|---|---|
| 0 | 2 |
| 1 | 4 |
| 2 | 6 |
| 3 | 8 |
| 4 | 10 |
Setting Array Values
While An Array’s length cannot be changed, however we can change the value of specific indices
assuming the array:
double[] x = new double[] {-1.32, 5.65, 3};
We can change the values of an array by doing almost the reverse of how we retrieved a value from an array:
double[] x = new double[] {-1.32, 5.65, 3};
x[0] = 3.14;
x[1] = 1.59;
x[2] = 2.65;
Retrieving The Length Of An Array
Retrieving the length of an array can be done by using the .length modifier. This type of syntax (known as the “dot” operator) will be explained more in the later section on Object-Oriented Programming, but for now think of it as a special property that any array has.
Consider the following example:
String[] message = new String[] {"hi,", "welcome", "to", "Montclair Robotics!"};
int x = message.length; // 4