Summary - Arrays

Combine declaring, filling and matrices to write a class list.

Summary - Arrays

In this group you learned arrays:

declaring: new int[n] and literals
access: arr[i] and arr.length
filling: index-based for
multi-dimensional: int[][] matrix
copying: System.arraycopy

These structures are the basic tools to process fixed-size data. Now combine them and write a class list.

Exercise Class list sum

Write a Main class with a main method. Assign {10, 20, 30} to int[] arr. Assign 0 to int sum. With for (int n : arr) do sum += n. Print the sum with System.out.println(sum).

Show example solution

public class Main {
    public static void main(String[] args) {
        int[] arr = {10, 20, 30};
        int sum = 0;
        for (int n : arr) {
            sum += n;
        }
        System.out.println(sum);
    }
}

Exercise Print a matrix element

Write a Main class with a main method. Assign {{1, 2}, {3, 4}} to int[][] m. Print the top-left element with System.out.println(m[0][0]).

Show example solution

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

Test yourself

Can an array's size change after creation?
- Only by adding
- Yes, always
- No, it is fixed
- Only by removing
Show answer

No, it is fixed — An array's size is fixed; it cannot change.
Match the array topics

new int[n]

Declaring
arr[i]

Access
int[][]

Matrix
arraycopy

Copying

Access the first element

int first = arr[____];

Show answer

int first = arr[0];

Next lesson: Arrays.sort

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