Arrays, thesarfo

So far we’ve only stored single values in a variable, but arrays let us store multiple values inside a single variable. To declare an array, you need a type keyword (e.g. char), followed by the name of the array, along with square brackets, and then assign it to a new object of that class, along with the size of the array in square brackets.

public class Main {
    public static void main(String[] args) {
        char vowels[] = new char[5]; // declaration

        vowels[0] = 'a'; // definition
        vowels[1] = 'e';
        vowels[2] = 'i';
        vowels[3] = 'o';
        vowels[4] = 'u';

        System.out.println(vowels[2]); // print out an element in the array
    }
}

When you use println to print an element in an array, that element is printed as a string, which means before printing the whole array you have to convert it into a string — by importing java.util.Arrays and using the toString() method.

import java.util.Arrays;

public class Main {
    public static void main(String[] args) {
        char vowels[] = new char[5];

        vowels[0] = 'a';
        vowels[1] = 'e';
        vowels[2] = 'i';
        vowels[3] = 'o';
        vowels[4] = 'u';

        System.out.println(Arrays.toString(vowels));
    }
}

Instead of declaring and defining your array on separate lines, you can do it all in one line.

import java.util.Arrays;

public class Main {
    public static void main(String[] args) {
        char vowels[] = {'a', 'e', 'i', 'o', 'u'}; // declare and define it

        vowels[1] = 'f'; // change the element in the array at index 1

        System.out.println(Arrays.toString(vowels));
    }
}

Array methods

Finding the length of an array

public class Main {
    public static void main(String[] args) {
        char vowels[] = {'a', 'e', 'i', 'o', 'u'};

        System.out.println(vowels.length);
    }
}

Sorting an unsorted array

import java.util.Arrays;

public class Main {
    public static void main(String[] args) {
        char vowels[] = {'e', 'i', 'a', 'u', 'o'};

        int startingIndex = 1;
        int endingIndex = 3;

        Arrays.sort(vowels); // sorts the array
        Arrays.sort(vowels, startingIndex, endingIndex); // sorts from index 1 to 3 (non-inclusive)

        System.out.println(Arrays.toString(vowels));
    }
}

Searching for a value in an array

import java.util.Arrays;

public class Main {
    public static void main(String[] args) {
        char vowels[] = {'a', 'e', 'i', 'o', 'u'};
        char key = 'o';

        int startingIndex = 0;
        int endingIndex = 4;

        Arrays.sort(vowels); // binarySearch only works on sorted arrays

        int foundItemIndex = Arrays.binarySearch(vowels, key); // returns the index of the key if found

        int anotherFoundItemIndex = Arrays.binarySearch(vowels, startingIndex, endingIndex, key); // can specify the start and end of the search

        System.out.println(foundItemIndex);
    }
}

Filling an array

You can fill an array with a value of your choice.

import java.util.Arrays;

public class Main {
    public static void main(String[] args) {
        char vowels[] = {'a', 'e', 'i', 'o', 'u'};

        Arrays.fill(vowels, 'x');

        System.out.println(Arrays.toString(vowels)); // outputs [x, x, x, x, x]

        // this fill method also works with a starting and ending index
    }
}

Creating a copy of an array

import java.util.Arrays;

public class Main {
    public static void main(String[] args) {
        int numbers[] = {1, 2, 3, 4, 5};

        int copyOfNumbers[] = Arrays.copyOf(numbers, numbers.length); // original array, then the length of the new array

        int startingIndex = 1;
        int endingIndex = 3; // can also serve as the length of the new array

        int anotherCopyOfNumbers[] = Arrays.copyOfRange(numbers, startingIndex, endingIndex); // same as above but you specify start/end indexes instead of a length

        System.out.println(Arrays.toString(numbers));
        System.out.println(Arrays.toString(copyOfNumbers));
    }
}

Comparing arrays

import java.util.Arrays;

public class Main {
    public static void main(String[] args) {
        int numbers[] = {1, 2, 3, 4, 5};
        int copyOfNumbers[] = Arrays.copyOf(numbers, numbers.length);

        System.out.println(Arrays.equals(numbers, copyOfNumbers)); // outputs true
    }
}