Java Level 5 Test

Knowing how to cook is not the same as running a restaurant kitchen. A restaurant also needs a supplier list, a way to taste every dish before it goes out, a notebook of what went wrong last night, and recipes that the next cook can follow. The last level of the course was about that side of Java: build tools, tests, mocks, logging, clean code, and the algorithms that interviewers like to ask about. This is the final test of the Learn track.

How the Test Works

• What's in it: 20 multiple-choice questions, then 3 puzzles where you work out what a short program prints, or how fast it runs.
• Time: 30 minutes, without notes, an IDE or JShell.
• Pass mark: 16 out of 23. The quiz marks the 20 questions for you. Mark the puzzles yourself, one point each, and add them to your quiz score.
• What it covers: the lessons from "Build Tools in Java: Maven and Gradle" to the interview preparation lessons.

Part 1: 20 Questions

Part 2: Puzzles

Work out each answer on paper before you open the solution. The solution shows a full program, its real output and a Try it button. Give yourself one point for each puzzle you get right.

Puzzle 1: Count the Steps

What is the time complexity of this code?

for (int i = 1; i < n; i *= 2)
    for (int j = 0; j < n; j++)
        count++;

The solution counts the steps for three sizes of n, so you can check your answer.

public class LoopCount {
    static long count(int n) {
        long count = 0;
        for (int i = 1; i < n; i *= 2) {
            for (int j = 0; j < n; j++) {
                count++;
            }
        }
        return count;
    }
 
    public static void main(String[] args) {
        for (int n : new int[] {8, 1024, 1_048_576}) {
            System.out.println("n = " + n + ": " + count(n) + " steps");
        }
    }
}

n = 8: 24 steps
n = 1024: 10240 steps
n = 1048576: 20971520 steps

Puzzle 2: Counting Words

What is printed?

Map<String, Integer> m = new HashMap<>();
for (String w : "to be or not to be".split(" ")) {
    m.merge(w, 1, Integer::sum);
}
System.out.println(new TreeMap<>(m));

import java.util.HashMap;
import java.util.Map;
import java.util.TreeMap;
 
public class WordCountPuzzle {
    public static void main(String[] args) {
        Map<String, Integer> m = new HashMap<>();
        for (String w : "to be or not to be".split(" ")) {
            m.merge(w, 1, Integer::sum);
        }
        System.out.println(new TreeMap<>(m));
    }
}

{be=2, not=1, or=1, to=2}

Puzzle 3: StringBuilder and String in a Method

What is printed?

public static void main(String[] args) {
    StringBuilder sb = new StringBuilder("abc");
    String s = "abc";
    change(sb, s);
    System.out.println(sb + " " + s);
}
 
static void change(StringBuilder sb, String s) {
    sb.append("d");
    s = s + "d";
}

public class BuilderPuzzle {
    public static void main(String[] args) {
        StringBuilder sb = new StringBuilder("abc");
        String s = "abc";
        change(sb, s);
        System.out.println(sb + " " + s);
    }
 
    static void change(StringBuilder sb, String s) {
        sb.append("d");
        s = s + "d";
    }
}

abcd abc

What Your Score Means