Free Java 17 OCP Practice Test 1

10 realistic exam questions for 1Z0-829 — with detailed explanations

Questions

20 min

Suggested Time

~65%

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📋 How This Practice Test Works

Select your answer for each question by clicking an option. When done with all 10 questions, click Submit & Show Answers at the bottom.

You'll see your score plus detailed explanations for every question — including why wrong answers are wrong.

These questions mirror the actual OCP exam style and difficulty. The real exam has 50 questions in 90 minutes.

Question 1

What is the output of the following code?

public class Main {
    sealed interface Shape permits Circle, Square {}
    record Circle(double radius) implements Shape {}
    record Square(double side) implements Shape {}

    public static String describe(Shape s) {
        return switch (s) {
            case Circle c -> "Circle: " + c.radius();
            case Square sq -> "Square: " + sq.side();
        };
    }

    public static void main(String[] args) {
        System.out.println(describe(new Circle(5.0)));
    }
}

ACircle: 5.0
BSquare: 5.0
CCompile error: pattern matching for switch requires default
DRuntime error

✅ Correct Answer: A

The switch expression uses pattern matching (introduced in Java 21, but available as preview in Java 17). Because Shape is a sealed interface that only permits Circle and Square, the compiler knows the switch is exhaustive — no default case needed. The Circle pattern matches and binds c, so c.radius() returns 5.0.

Question 2

Given the record below, what is the output?

public record Point(int x, int y) {
    public Point {
        if (x < 0 || y < 0) {
            throw new IllegalArgumentException("Negative");
        }
    }
}

// In main:
Point p = new Point(3, 4);
System.out.println(p.x() + ", " + p.y());

A3.0, 4.0
B3, 4
CCompile error: cannot throw from compact constructor
DIllegalArgumentException is thrown

✅ Correct Answer: B

The compact constructor public Point { ... } validates parameters before the canonical constructor assigns them. Since x=3 and y=4 are both non-negative, no exception is thrown. Record accessor methods are x() and y() (not getX()/getY()). The output is "3, 4".

Question 3

What is the output?

import java.util.stream.*;
import java.util.*;

List<Integer> nums = List.of(1, 2, 3, 4, 5);
int result = nums.stream()
    .filter(n -> n % 2 == 0)
    .mapToInt(Integer::intValue)
    .sum();
System.out.println(result);

✅ Correct Answer: B

The filter keeps only even numbers: 2 and 4. The mapToInt converts the Stream<Integer> to IntStream. The sum() terminal operation returns 2 + 4 = 6.

Question 4

Which statement about the Java Platform Module System (JPMS) is correct?

AThe module-info.java file must be in the META-INF directory
BA module can use requires and exports in the same declaration
Crequires transitive makes the required module available to modules that depend on this one
DThe opens directive is identical to exports

✅ Correct Answer: C

requires transitive M; means that any module reading the current module will also implicitly read module M. This is "implied readability".

Why others are wrong: (A) module-info.java must be in the root of the module source, not META-INF. (B) requires and exports are separate directives. (D) opens allows deep reflection at runtime, while exports only allows compile-time access to public types.

Question 5

What is the output?

import java.util.function.*;

Function<Integer, Integer> doubler = x -> x * 2;
Function<Integer, Integer> addOne = x -> x + 1;

Function<Integer, Integer> combined = doubler.andThen(addOne);
System.out.println(combined.apply(3));

✅ Correct Answer: A

f.andThen(g) means apply f first, then g. So doubler.andThen(addOne).apply(3) → addOne.apply(doubler.apply(3)) → addOne.apply(6) → 7. Note this is different from compose, which applies in reverse order.

Question 6

What is the output?

try {
    throw new RuntimeException("outer");
} catch (RuntimeException e) {
    try {
        throw new IllegalStateException("inner");
    } catch (IllegalStateException e2) {
        e.addSuppressed(e2);
    }
    System.out.println(e.getSuppressed().length);
}

A0
B1
C2
DCompile error

✅ Correct Answer: B

addSuppressed(Throwable) attaches the inner exception to the outer one as a suppressed exception. getSuppressed() returns an array of suppressed throwables, which contains exactly 1 element (the IllegalStateException).

Question 7

What is true about the following code?

import java.nio.file.*;

Path p = Paths.get("/data", "logs", "app.log");
Path normalized = p.normalize();
System.out.println(normalized);

AIt prints "/data/logs/app.log" (or "\data\logs\app.log" on Windows)
BIt prints "data/logs/app.log" without leading slash
CIt throws IOException because the file doesn't exist
DIt throws NoSuchFileException

✅ Correct Answer: A

Paths.get(String, String...) creates a Path object — it doesn't access the file system. normalize() only removes redundant elements like ".." and "." — since this path has no redundancies, it returns the same logical path. Path operations like get() and normalize() never throw IOException because they only manipulate path strings, not the file system.

Question 8

What is the output?

import java.util.concurrent.*;

ExecutorService executor = Executors.newFixedThreadPool(2);
Future<Integer> future = executor.submit(() -> 42);
System.out.println(future.get());
executor.shutdown();

A42
BFuture@somehash
C0
DCompile error: lambda is not a Callable

✅ Correct Answer: A

executor.submit() accepts a Callable<V>, and the lambda () -> 42 is compatible with Callable<Integer> (returns a value). The future.get() call blocks until the task completes, then returns the value 42. The blocking call also handles checked exceptions InterruptedException and ExecutionException (assume try-catch or throws in actual exam scenarios).

Question 9

Which option correctly demonstrates JDBC PreparedStatement usage?

Astmt.setString(0, "Alice"); (parameter index starts at 0)
BYou must call stmt.commit() after each query for it to execute
Cstmt.setString(1, "Alice"); (parameter index starts at 1)
DPreparedStatement does not protect against SQL injection

✅ Correct Answer: C

JDBC parameter indices are 1-based, not 0-based. This is a common exam trap.

Why others are wrong: (A) Index starts at 1. (B) Commit is for transactions, not individual queries. (D) PreparedStatement IS the main protection against SQL injection in Java — that's its core benefit.

Question 10

What is the output?

import java.util.*;
import java.util.stream.*;

Optional<String> result = Stream.of("apple", "banana", "cherry")
    .filter(s -> s.startsWith("z"))
    .findFirst();
    
System.out.println(result.orElse("nothing"));

Anull
Bapple
Cnothing
DNoSuchElementException

✅ Correct Answer: C

No string in the stream starts with "z", so filter produces an empty stream and findFirst() returns Optional.empty(). The orElse("nothing") method returns the default value when the Optional is empty. Output: "nothing".

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