Java Level 3 Test

A new cook in a busy kitchen doesn't need to invent recipes. What they need is to know where every tool is and which one fits each job: the sharp knife, not the bread knife, for onions. This level of the course was about Java's kitchen drawer: strings, exceptions, generics, collections, streams, dates and files. This test checks that you reach for the right tool, and that you know how the most used ones, like HashMap, work inside.

How the Test Works

• What's in it: 20 multiple-choice questions, then 3 output puzzles where you work out what a short program prints.
• 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 "Strings in Java" to serialization.

Part 1: 20 Questions

Part 2: Output Puzzles

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

Puzzle 1: Built at Runtime

What is printed?

String s1 = "Java";
String s2 = "Ja";
String s3 = s2 + "va";
System.out.println(s1 == s3);
System.out.println(s1 == s3.intern());

public class InternPuzzle {
    public static void main(String[] args) {
        String s1 = "Java";
        String s2 = "Ja";
        String s3 = s2 + "va";
        System.out.println(s1 == s3);
        System.out.println(s1 == s3.intern());
    }
}

false
true

Puzzle 2: Return and Finally

What is printed?

static int test() {
    try {
        return 1;
    } finally {
        System.out.print("finally ");
    }
}
 
// in main:
System.out.println(test());

public class FinallyPuzzle {
    static int test() {
        try {
            return 1;
        } finally {
            System.out.print("finally ");
        }
    }
 
    public static void main(String[] args) {
        System.out.println(test());
    }
}

finally 1

Puzzle 3: A Short Stream

What is printed?

List<String> names = List.of("Navika", "Srihitha", "Advitha");
System.out.println(names.stream()
        .filter(n -> n.length() > 6)
        .map(String::toUpperCase)
        .sorted()
        .toList());

import java.util.List;
 
public class StreamPuzzle {
    public static void main(String[] args) {
        List<String> names = List.of("Navika", "Srihitha", "Advitha");
        System.out.println(names.stream()
                .filter(n -> n.length() > 6)
                .map(String::toUpperCase)
                .sorted()
                .toList());
    }
}

[ADVITHA, SRIHITHA]

What Your Score Means