Java Refresh Test (Java 9 to 25)

Coming back to a city you lived in years ago is a strange feeling. The streets are where you left them, but there is a new metro line, your old shortcut is now one-way, and everyone pays with their phone. Java after Java 8 feels the same. The language you knew still works, but there are records, var, text blocks, switch expressions, pattern matching, virtual threads and a new release every six months. This test is for the Refresh track. Every question is about a feature added in Java 9 or later.

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: language, library and JVM features from Java 9 to Java 25. Start with Java 9 to 11 Features if most of these are new to you.

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: First, Last and Reversed

What is printed? (Java 21 or later)

var list = new ArrayList<>(List.of(3, 1, 2));
list.addFirst(0);
System.out.println(list.reversed());

import java.util.ArrayList;
import java.util.List;
 
public class SequencedPuzzle {
    public static void main(String[] args) {
        var list = new ArrayList<>(List.of(3, 1, 2));
        list.addFirst(0);
        System.out.println(list.reversed());
    }
}

[2, 1, 3, 0]

Puzzle 2: A Guarded Case

What is printed?

Object o = 42;
String r = switch (o) {
    case Integer i when i > 40 -> "big int " + i;
    case Integer i -> "int " + i;
    case String s -> "string " + s;
    default -> "other";
};
System.out.println(r);

public class GuardPuzzle {
    public static void main(String[] args) {
        Object o = 42;
        String r = switch (o) {
            case Integer i when i > 40 -> "big int " + i;
            case Integer i -> "int " + i;
            case String s -> "string " + s;
            default -> "other";
        };
        System.out.println(r);
    }
}

big int 42

Puzzle 3: Counting Lines in a Text Block

What is printed?

String json = """
    {
      "name": "Java"
    }
    """;
System.out.println(json.lines().count());

public class TextBlockPuzzle {
    public static void main(String[] args) {
        String json = """
            {
              "name": "Java"
            }
            """;
        System.out.println(json.lines().count());
    }
}

3

What Your Score Means