Week 2 mini challenge: Number Toolkit

Practical review day

1 Learn

Review day! Week 2 covered methods, parameters, return values, arrays and Strings.

Build a small toolkit of methods and use them from main — this is how larger programs are organized.

2 See the Code

Java

public class Toolkit {
    static int max(int[] a) {
        int m = a[0];
        for (int x : a) if (x > m) m = x;
        return m;
    }

    static String reverse(String s) {
        String r = "";
        for (int i = s.length() - 1; i >= 0; i--) r += s.charAt(i);
        return r;
    }

    public static void main(String[] args) {
        int[] nums = {4, 19, 7, 12};
        System.out.println("Max: " + max(nums));
        System.out.println("Reverse: " + reverse("java"));
    }
}

max() walks through the array keeping the biggest value.
reverse() builds a new String from the last character to the first.

Output

Max: 19
Reverse: avaj

3 Practice

Challenge 1: Add min(int[] a).
Challenge 2: Add isPalindrome(String s) using reverse() and equals().
Challenge 3: Add sum(int[] a) and print the average using it.

Try it in your own Java setup or write it in the Practice Notebook.

4 Quick Check

1. reverse("abc") returns?
2. Which is a palindrome?
3. What must max() do with its result?

Step 5

Answer and check the Quick Check above to unlock this.

Day 13