Oracle Java SE 17 Developer Practice Test (1Z0-829)
Oracle Java SE 17 Developer Practice Test
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Questions updated at Aug 29, 2026, 11:44 PM CDT
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Today's 10 Oracle Java SE 17 Developer questions
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Question 1 of 10
Objective Access control protected across packages
Domain 3: Utilizing Java Object-Oriented Approach
Class `Child` in package `p2` extends `Base` in package `p1`; `Base` declares `protected int value`. From an instance method of `Child`, which access is legal when `other` has static type `Base` and `this` is a `Child`?
Across package boundaries, a subclass may access an inherited protected instance member through the subclass context, such as `this`; it may not use an arbitrary `Base` instance reference.
Concept tested:
Question 2 of 10
Objective CompletableFuture transformation
Domain 8: Managing Concurrent Code Execution
What is the eventual result? ```java CompletableFuture<Integer> f = CompletableFuture.completedFuture(10) .thenApply(x -> x * 2); System.out.println(f.join()); ```
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Concept tested:
Question 3 of 10
Objective Pattern matching for switch status in Java 17
Domain 2: Controlling Program Flow
A code review proposes using type patterns directly in a `switch` over an `Object`. The build uses normal `javac --release 17` without preview features. What should the reviewer conclude?
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Question 4 of 10
Objective DateTimeFormatter pattern letters
Domain 1: Handling Date, Time, Text, Numeric and Boolean Values
A log formatter must print `2026-08-28 17:05` from a `LocalDateTime`. Which formatter pattern uses calendar year, month, day, 24-hour clock, and minute correctly?
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Concept tested:
Question 5 of 10
Objective Unmodifiable view backing collection
Domain 5: Working with Arrays and Collections
A service wraps a list: ```java var source = new ArrayList<>(List.of("A", "B")); var view = Collections.unmodifiableList(source); source.set(0, "X"); System.out.println(view); ``` What is printed?
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Concept tested:
Question 6 of 10
Objective Locale language tag
Domain 11: Implementing Localization
Which Java 17 expression creates a locale from the BCP 47 language tag for Canadian French, `fr-CA`?
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Question 7 of 10
Objective Stream.toList mutability
Domain 6: Working with Streams and Lambda Expressions
A service executes: ```java List<String> out = Stream.of("A", "B").toList(); out.add("C"); ``` What happens in Java 17?
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Question 8 of 10
Objective Checked exception propagation
Domain 4: Handling Exceptions
A method is declared: ```java static void load() throws IOException { ... } ``` A caller neither catches `IOException` nor declares it. What happens?
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Question 9 of 10
Objective Path resolve absolute operand
Domain 9: Using Java I/O API
A path-composition helper runs on a Unix-like file system: ```java Path base = Path.of("/opt/app"); Path other = Path.of("/tmp/data"); System.out.println(base.resolve(other)); ``` Which path is printed?
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Question 10 of 10
Objective opens does not grant ordinary private access
Domain 7: Packaging and Deploying Java Code and Using JPMS
Module `client` wants to directly compile `new InternalType()` where `InternalType` is package-private in another module. That package is `opens ... to client` but is not exported. What should you expect?
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1Z0-829 Oracle Java SE 17 Developer
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Question 1 Class `Child` in package `p2` extends `Base` in package `p1`; `Base` declares `protected int value`. From an instance method of `Child`, which access is legal when `other` has static type `Base` and `this` is a `Child`?
Answer choices
- A. `this.value`
- B. `other.value`
- C. `new Base().value`
- D. `Base.value`
Correct answer
`this.value`
Across package boundaries, a subclass may access an inherited protected instance member through the subclass context, such as `this`; it may not use an arbitrary `Base` instance reference.
Wrong-answer review
- B. `other.value`: Incorrect. An arbitrary superclass-typed instance from another package does not satisfy the protected access rule.
- C. `new Base().value`: Incorrect. Constructing another `Base` does not grant package or subclass-qualified access to its protected member.
- D. `Base.value`: Incorrect. The member is an instance field, not a static field.
Extra learning features
Interview question
Q: Across package boundaries, a subclass may access an inherited protected instance member through the subclass context, such as `this`; it may not use an arbitrary `Base` instance reference. This is crucial for maintaining encapsulation and preventing unintended access to internal implementation details of the base class. Without this restriction, subclasses could potentially expose sensitive data or modify the base class's state in unexpected ways, leading to instability and difficult-to-debug issues. Strong answer: Across package boundaries, a subclass may access an inherited protected instance member through the subclass context, such as `this`; it may not use an arbitrary `Base` instance reference.
- protected access
- encapsulation
- instance member
- subclass context
- arbitrary Base instance reference
Caution: This is a fundamental aspect of Java's object model, and understanding it is critical for writing robust and maintainable code.
Why this matters
Incorrect access control can lead to vulnerabilities. Allowing unrestricted access to protected members from subclasses could expose sensitive data or enable malicious code to manipulate the base class's state, resulting in security breaches and data corruption. This has significant consequences for system integrity and user trust.
Question 2 What is the eventual result? ```java CompletableFuture<Integer> f = CompletableFuture.completedFuture(10) .thenApply(x -> x * 2); System.out.println(f.join()); ```
Answer choices
- A. `null`
- B. `10`
- C. `12`
- D. `20`
Correct answer
`20`
Question 3 A code review proposes using type patterns directly in a `switch` over an `Object`. The build uses normal `javac --release 17` without preview features. What should the reviewer conclude?
Answer choices
- A. Only add `default`; that makes type patterns standard Java 17 syntax.
- B. Use it freely because pattern matching for `switch` is a permanent Java 17 feature.
- C. Replace every type pattern with a record pattern; record patterns are standard in Java 17.
- D. Without preview enabled, type patterns in `switch` are unavailable in Java 17.
Correct answer
Without preview enabled, type patterns in `switch` are unavailable in Java 17.
Question 4 A log formatter must print `2026-08-28 17:05` from a `LocalDateTime`. Which formatter pattern uses calendar year, month, day, 24-hour clock, and minute correctly?
Answer choices
- A. `YYYY-MM-dd hh:mm`
- B. `YYYY-mm-DD hh:MM`
- C. `yyyy-mm-dd HH:MM`
- D. `yyyy-MM-dd HH:mm`
Correct answer
`yyyy-MM-dd HH:mm`
Question 5 A service wraps a list: ```java var source = new ArrayList<>(List.of("A", "B")); var view = Collections.unmodifiableList(source); source.set(0, "X"); System.out.println(view); ``` What is printed?
Answer choices
- A. `[A, B]`
- B. An `UnsupportedOperationException` is thrown by `source.set`.
- C. `[X, B]`
- D. The view becomes empty because the wrapper is invalidated.
Correct answer
`[X, B]`
Question 6 Which Java 17 expression creates a locale from the BCP 47 language tag for Canadian French, `fr-CA`?
Answer choices
- A. `Locale.of("fr", "CA")`
- B. `new Locale("fr_CA")`
- C. `Locale.forLanguageTag("fr-CA")`
- D. `Locale.forLanguageTag("fr_CA")`
Correct answer
`Locale.forLanguageTag("fr-CA")`
Question 7 A service executes: ```java List<String> out = Stream.of("A", "B").toList(); out.add("C"); ``` What happens in Java 17?
Answer choices
- A. The list accepts `C` only if the source stream is sequential.
- B. The list becomes `[A, B, C]`.
- C. The `add` call throws `UnsupportedOperationException` because `Stream.toList()` returns an unmodifiable list.
- D. The code fails to compile because `toList()` was added after Java 17.
Correct answer
The `add` call throws `UnsupportedOperationException` because `Stream.toList()` returns an unmodifiable list.
Question 8 A method is declared: ```java static void load() throws IOException { ... } ``` A caller neither catches `IOException` nor declares it. What happens?
Answer choices
- A. The `throws` clause affects documentation only.
- B. Compilation fails unless `IOException` is caught or declared.
- C. The exception is automatically converted to `RuntimeException`.
- D. The code compiles and the JVM logs the exception if it occurs.
Correct answer
Compilation fails unless `IOException` is caught or declared.
Question 9 A path-composition helper runs on a Unix-like file system: ```java Path base = Path.of("/opt/app"); Path other = Path.of("/tmp/data"); System.out.println(base.resolve(other)); ``` Which path is printed?
Answer choices
- A. `/opt/app/../tmp/data`
- B. The code throws `IllegalArgumentException`.
- C. `/opt/app/tmp/data`
- D. `/tmp/data`
Correct answer
`/tmp/data`
Question 10 Module `client` wants to directly compile `new InternalType()` where `InternalType` is package-private in another module. That package is `opens ... to client` but is not exported. What should you expect?
Answer choices
- A. The JVM automatically treats every type in an opened package as public.
- B. Direct source-level access still fails; `opens` is for reflective access and does not make a package-private type an ordinary accessible API.
- C. The code compiles because `opens` is stronger than `exports` for all access.
- D. The code compiles only if the constructor is `protected`.
Correct answer
Direct source-level access still fails; `opens` is for reflective access and does not make a package-private type an ordinary accessible API.
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