The short way to create an array

Creating an array with its values

When you know the values as you write the program, list them in braces:

int[] values = {3, 1, 4};
String[] days = {"Mon", "Tue", "Wed"};
System.out.println(values.length);
System.out.println(days[2]);

3
Wed

Java counts the values and makes an array of that size, so {3, 1, 4} does the same as new int[3] followed by three assignments. The braces alone work only in the line that declares the variable. Anywhere else, such as in a method call, write new int[] in front of them: total(new int[] {3, 1, 4}).

Printing an array

Printing the array variable itself doesn't print the values:

int[] values = {3, 1, 4};
System.out.println(values);

This prints [I@ followed by a code of letters and digits, which can change from one run to the next. [I stands for "array of int", and the code says nothing about the values. To see them, you can print the elements with a loop, as in the earlier steps. Or let Java do it: Arrays.toString gives the values as text, in square brackets. It lives in the class java.util.Arrays, which needs an import line, as Scanner does:

import java.util.Arrays;

public class Main {
    public static void main(String[] args) {
        int[] values = {3, 1, 4};
        String[] days = {"Mon", "Tue", "Wed"};
        System.out.println(Arrays.toString(values));
        System.out.println(Arrays.toString(days));
    }
}

[3, 1, 4]
[Mon, Tue, Wed]

It's a handy tool for checking what an array holds while you work on a program.

Array or list?

A list is the everyday choice when the number of values changes or isn't known in advance: reading until the user stops, or a to-do list that items come and go from. An array fits when the size is fixed and known, like the seven days of a week. It's especially good for counting, when the value itself can be the index.

Counting with an array

Each line of input here is a vote for option 1, 2 or 3, until a 0. The line votes[option]++; adds one to that option's counter. The array has four places so that options 1 to 3 can use their own number as the index; index 0 is simply never used.

import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        int[] votes = new int[4];
        while (true) {
            int option = Integer.valueOf(scanner.nextLine());
            if (option == 0) {
                break;
            }
            votes[option]++;
        }
        for (int option = 1; option < votes.length; option++) {
            System.out.println("Option " + option + ": " + votes[option]);
        }
    }
}

2
3
2
1
2
0

Option 1: 1
Option 2: 3
Option 3: 1

Without an array, this would take a separate counter and an if for each option. With one, counting 30 options instead of 3 changes only the size of the array.