Arrays and strings

Declaring and initializing arrays

In Java, an array is a collection of variables of the same data type. You can declare an array by specifying its data type, followed by square brackets ([]), and then the array name. You can then initialize the array by specifying its length and assigning values to each element. Here's an example:

public class ArrayExample {
    public static void main(String[] args) {
        int[] numbers = new int[3];
        numbers[0] = 1;
        numbers[1] = 2;
        numbers[2] = 3;
        System.out.println(numbers[0]);
        System.out.println(numbers[1]);
        System.out.println(numbers[2]);
    }
}

In the above example, we declare an integer array called numbers with a length of 3. We then assign the values 1, 2, and 3 to the first, second, and third elements of the array, respectively. We then print the values of the first, second, and third elements to the console.

Accessing array elements

You can access elements of an array using their index number, which starts at 0 for the first element. Here's an example:

public class ArrayAccessExample {
    public static void main(String[] args) {
        int[] numbers = {1, 2, 3};
        System.out.println(numbers[0]);
        System.out.println(numbers[1]);
        System.out.println(numbers[2]);
    }
}

In the above example, we declare and initialize an integer array called numbers with the values 1, 2, and 3. We then print the values of the first, second, and third elements to the console.

Multi-dimensional arrays

In Java, you can also create multi-dimensional arrays, which are arrays of arrays. Here's an example of a two-dimensional array:

public class TwoDArrayExample {
    public static void main(String[] args) {
        int[][] matrix = {{1, 2}, {3, 4}};
        System.out.println(matrix[0][0]); // prints 1
        System.out.println(matrix[0][1]); // prints 2
        System.out.println(matrix[1][0]); // prints 3
        System.out.println(matrix[1][1]); // prints 4
    }
}

In the above example, we declare and initialize a two-dimensional integer array called matrix with the values 1, 2, 3, and 4. We then print each element of the matrix to the console.

Working with strings

In Java, a string is a sequence of characters. You can declare a string variable by specifying its data type as String, and then assigning a string value to it. Here's an example:

public class StringExample {
    public static void main(String[] args) {
        String greeting = "Hello, world!";
        System.out.println(greeting);
    }
}

In the above example, we declare a string variable called greeting with the value "Hello, world!". We then print the value of greeting to the console.

You can also concatenate strings using the + operator, or use methods to manipulate strings. Here are some examples:

public class StringConcatExample {
    public static void main(String[] args) {
        String firstName = "John";
        String lastName = "Doe";
        String fullName = firstName + " " + lastName;
        System.out.println(fullName); // prints "John Doe"

        String phrase = "Hello,world!";
        int length = phrase.length();
        System.out.println(length); // prints 13
    }
}

In the above example, we declare two string variables firstName and lastName, and concatenate them to create a fullName variable. We then print the value of fullName to the console.

We also demonstrate the use of the length() method of the String class, which returns the length of the string.

That covers the basics of arrays and strings in Java!