Oracle Certified Professional: Java SE 17 Developer Practice Test

Oracle Certified Professional: Java SE 17 Developer Certification is a testament to your deep understanding and proficiency in Java language and its associated technologies. As you prepare to take this esteemed certification, practice is key to ensuring your success. Below are 40 multiple-choice questions, each accompanied by the correct answer and detailed explanations to deepen your understanding and prepare you thoroughly.

1. What is the default value of an instance variable of type int in Java?

A) 0
B) null
C) undefined
D) Not initialized

Answer:

A) 0

Explanation:

In Java, the default value of an instance variable of type int is 0. Instance variables are given default values when they are declared and not explicitly initialized.

2. Which of the following is a valid method declaration in Java?

A) public int myMethod() {}
B) int myMethod() {}
C) public void myMethod(int a, int b) {}
D) All of the above

Answer:

D) All of the above

Explanation:

All of the given options are valid method declarations in Java. A method must have a return type, a name, and a parameter list enclosed in parentheses.

3. How do you create a single-line comment in Java?

A) // This is a comment
B) /* This is a comment */
C) <!– This is a comment –>
D) # This is a comment

Answer:

A) // This is a comment

Explanation:

In Java, single-line comments are created using two forward slashes (//), followed by the comment.

4. Which of the following Java keywords is used to define a constant variable?

A) static
B) final
C) const
D) immutable

Answer:

B) final

Explanation:

The "final" keyword in Java is used to create constant variables. Once a final variable is assigned a value, it cannot be modified.

5. What is the role of the Java Virtual Machine (JVM)?

A) To compile Java source code to bytecode
B) To interpret and execute Java bytecode on any platform
C) To create Java documentation
D) To debug Java programs

Answer:

B) To interpret and execute Java bytecode on any platform

Explanation:

The Java Virtual Machine (JVM) is a runtime environment that interprets and executes Java bytecode, enabling Java programs to be platform-independent.

6. Which of the following is a correct way to allocate memory to an array in Java?

A) int arr[] = new int[5];
B) int arr[] = new int[];
C) int arr[] = new [5]int;
D) int arr[] = int[5];

Answer:

A) int arr[] = new int[5];

Explanation:

In Java, memory for an array can be allocated using the ‘new’ keyword followed by the data type and the size of the array enclosed in square brackets.

7. How can you handle exceptions in Java?

A) Using try and catch blocks
B) Using if and else statements
C) Using loops
D) Using pointers

Answer:

A) Using try and catch blocks

Explanation:

In Java, exceptions can be handled using try and catch blocks. The code that might throw an exception is placed inside the try block, and the code to handle the exception is placed inside the catch block.

8. Which of the following is an interface in the Java Collections Framework?

A) ArrayList
B) HashMap
C) TreeMap
D) List

Answer:

D) List

Explanation:

In the Java Collections Framework, List is an interface, whereas ArrayList, HashMap, and TreeMap are classes.

9. What is the purpose of the ‘this’ keyword in Java?

A) To refer to the current object
B) To refer to the static members of a class
C) To create a new object
D) To refer to the parent class

Answer:

A) To refer to the current object

Explanation:

The ‘this’ keyword in Java is used to refer to the current object within an instance method or constructor.

10. Which of the following is true about method overloading in Java?

A) Method overloading allows a class to have multiple methods with the same name, but different return types.
B) Method overloading allows a class to have multiple methods with the same name and the same parameter list.
C) Method overloading is determined at runtime.
D) None of the above.

Answer:

D) None of the above.

Explanation:

Method overloading in Java occurs when a class has multiple methods with the same name but different parameter lists. The return type is not considered while differentiating overloaded methods.

11. Which Java feature allows one interface to inherit from another interface?

A) Multithreading
B) Polymorphism
C) Inheritance
D) Encapsulation

Answer:

C) Inheritance

Explanation:

In Java, one interface can inherit from another interface using the extends keyword. This is a form of inheritance, which is a fundamental concept of object-oriented programming.

12. Which of the following statements is true about constructors in Java?

A) Constructors must have a return type.
B) Constructors are used to initialize the newly created object.
C) Constructors can be inherited.
D) Constructors can be private, protected, or public, but not default.

Answer:

B) Constructors are used to initialize the newly created object.

Explanation:

A constructor in Java is a special method used to initialize objects. It is called when an instance of an object is created and doesn’t have a return type.

13. In Java, which method must be implemented by a class using the Runnable interface for creating a thread?

A) init()
B) start()
C) run()
D) threadRun()

Answer:

C) run()

Explanation:

In Java, a class that implements the Runnable interface must override the run() method. This method contains the code that constitutes the new thread’s body.

14. Which class should be used to perform operations such as reading and writing data to/from files in Java?

A) FileReader
B) FileWriter
C) BufferedReader
D) Both A and B

Answer:

D) Both A and B

Explanation:

In Java, FileReader is used for reading character files, and FileWriter is used for writing characters to a file. Being Reader derived, FileReader makes the form of characters correct and provides efficient reading of characters, arrays, and lines.

15. How can we ensure that a resource is closed automatically when try block finishes, and we don’t need to close it explicitly?

A) By using a finally block
B) By using try-with-resources statement
C) By using the close() method
D) None of the above

Answer:

B) By using try-with-resources statement

Explanation:

In Java 7 and later, we can use the try-with-resources statement to automatically close resources like File, Socket, etc., when the try block finishes, and there is no need to close them explicitly.

16. Which of the following loops will execute the statements within it at least once?

A) for loop
B) while loop
C) do-while loop
D) None of the above

Answer:

C) do-while loop

Explanation:

In Java, a do-while loop is guaranteed to execute the statements within it at least once, because the condition is checked after the body of the loop is executed.

17. Which of the following Java operators is used to allocate memory for an object?

A) new
B) malloc
C) alloc
D) sizeof

Answer:

A) new

Explanation:

In Java, the "new" operator is used to allocate memory for an object and invoke the object's constructor.

18. Which of the following is used to define a module in Java 17?

A) module.java
B) module-info.java
C) module-def.java
D) module-class.java

Answer:

B) module-info.java

Explanation:

In Java, a module is defined using a module descriptor, which is placed in a file named module-info.java.

19. How do you create a sealed class in Java 17?

A) Using the sealed keyword
B) Using the final keyword
C) Using the sealed() method
D) Sealed classes are not supported in Java 17

Answer:

A) Using the sealed keyword

Explanation:

In Java 17, you can create a sealed class using the sealed keyword, followed by the class declaration, permitting specific classes to extend it.

20. Which of the following methods release resources or perform cleanup when a pattern variable goes out of scope in Java 17?

A) finalize()
B) close()
C) exit()
D) terminate()

Answer:

B) close()

Explanation:

Java 17 introduces the close() method which gets called when a pattern variable goes out of scope, ensuring resources are released, or necessary cleanup is performed.

21. Which of the following is a direct superclass of all exception classes in Java?

A) RuntimeException
B) Throwable
C) Exception
D) Error

Answer:

B) Throwable

Explanation:

In Java, the Throwable class is the superclass of all errors and exceptions in the Java language.

22. How can you create an immutable list in Java 17?

A) List.of()
B) List.copyOf()
C) Collections.unmodifiableList()
D) All of the above

Answer:

D) All of the above

Explanation:

Java 17 provides several methods to create immutable lists, including List.of(), List.copyOf(), and Collections.unmodifiableList().

23. What is the primary purpose of JShell in Java 17?

A) Debugging
B) Compiling
C) Interactive Java Shell
D) Unit Testing

Answer:

C) Interactive Java Shell

Explanation:

JShell is an interactive Java shell tool in Java 17, which allows the execution of Java code snippets and expressions interactively in a command-line interface.

24. Which of the following annotations denotes that a record component or a record is local to the implementation and is not an API element in Java 17?

A) @LocalRecord
B) @HiddenComponent
C) @Hidden
D) @Incubating

Answer:

C) @Hidden

Explanation:

The @Hidden annotation in Java is used to indicate that a record component or a record is not an API element and is local to the implementation. This annotation can be used to hide specific elements during the generation of Javadocs or other documentation tools.

25. In Java 17, what is the result of trying to modify an unmodifiable collection?

A) The operation will succeed silently.
B) The operation will throw an UnsupportedOperationException.
C) The collection will become modifiable.
D) The collection will be cloned, and the clone will be modified.

Answer:

B) The operation will throw an UnsupportedOperationException.

Explanation:

Trying to modify an unmodifiable collection in Java 17 will result in an UnsupportedOperationException being thrown.

26. How can you avoid NullPointerException in Java 17 when calling an instance method?

A) By using Optional class
B) By using try-catch block
C) By using the Objects.requireNonNull() method
D) By using Pattern Matching for instanceof

Answer:

A) By using Optional class

Explanation:

The Optional class in Java 17 provides a way to represent optional values and can be used to avoid NullPointerException when calling an instance method.

27. Which of the following features was introduced in Java 17 to enhance the switch statement/expression by allowing pattern matching and deconstruction?

A) Sealed Classes
B) Record Classes
C) Value-based Classes
D) Pattern Matching for switch

Answer:

D) Pattern Matching for switch

Explanation:

Pattern Matching for switch was introduced in Java 17 to enhance the switch statement/expression by allowing pattern matching and deconstruction.

28. What is the purpose of the permits clause in a sealed class declaration in Java 17?

A) It specifies the classes that are allowed to extend the sealed class.
B) It grants permissions to the sealed class.
C) It restricts the accessibility of the sealed class.
D) It permits the instantiation of the sealed class.

Answer:

A) It specifies the classes that are allowed to extend the sealed class.

Explanation:

The permits clause in a sealed class declaration specifies which classes are permitted to extend or implement the sealed class.

29. Which of the following is true regarding Text Blocks in Java 17?

A) They are used to represent multi-line string literals.
B) They start with three double quote characters (""").
C) They can contain escape sequences.
D) All of the above.

Answer:

D) All of the above.

Explanation:

Text Blocks in Java 17 are used for representing multi-line string literals. They start with three double quote characters (""") and can contain escape sequences.

30. Which Java 17 feature allows the developer to express the schema of data in a concise, immutable, and null-safe way?

A) Sealed Classes
B) Record Classes
C) Value-based Classes
D) Text Blocks

Answer:

B) Record Classes

Explanation:

Record Classes in Java 17 allow developers to model immutable data in applications in a quick, convenient, and safe manner. They help in expressing the schema of data concisely.

31. What is the default behavior of the equals() method in a record class in Java 17?

A) It checks for reference equality.
B) It checks for structural equality based on the record components.
C) It always returns true.
D) It always returns false.

Answer:

B) It checks for structural equality based on the record components.

Explanation:

By default, the equals() method in a record class in Java 17 checks for structural equality based on the values of the record components.

32. In Java 17, which class should you use for a resizable array-based implementation of the List interface?

A) LinkedList
B) ArrayList
C) Vector
D) Stack

Answer:

B) ArrayList

Explanation:

In Java 17, ArrayList is the class used for a resizable-array implementation of the List interface. It is part of the Java Collections Framework.

33. How can encapsulation in Java help in protecting the integrity of the objects?

A) By making all members of a class public.
B) By making all members of a class static.
C) By restricting unauthorized access and modification of class members.
D) By allowing unrestricted access to class members.

Answer:

C) By restricting unauthorized access and modification of class members.

Explanation:

Encapsulation in Java helps protect the integrity of the objects by restricting unauthorized access and modification of class members through the use of access modifiers.

34. What is the advantage of using Lambda Expressions in Java?

A) They allow the creation of anonymous methods.
B) They increase code verbosity.
C) They can replace loop statements.
D) They can throw any checked exception.

Answer:

A) They allow the creation of anonymous methods.

Explanation:

Lambda Expressions in Java allow us to write instances of single-method interfaces (functional interfaces) in a much more concise, expressive, and readable way, thereby allowing the creation of anonymous methods.

35. Which of the following is NOT a feature of the Java 17 sealed keyword?

A) It restricts which other classes or interfaces may extend or implement them.
B) It permits classes outside its module.
C) It can be used with classes, interfaces, and records.
D) It provides a way to represent algebraic data types.

Answer:

B) It permits classes outside its module.

Explanation:

The sealed keyword does not permit classes from outside its module to extend or implement them. The permits clause is used to specify which classes are allowed.

36. What is the purpose of the yield statement in a switch expression in Java 17?

A) It breaks out of the switch expression.
B) It returns a value from the switch expression.
C) It yields control to the next case.
D) It throws an exception.

Answer:

B) It returns a value from the switch expression.

Explanation:

In Java 17, the yield statement is used to return a value from a switch expression.

37. Which Java interface is part of the Java Collections Framework and represents a collection that does not allow duplicate elements?

A) List
B) Set
C) Map
D) Queue

Answer:

B) Set

Explanation:

The Set interface in Java is part of the Java Collections Framework and represents a collection that does not allow duplicate elements.

38. In Java 17, which method can be used to obtain the Class object associated with the class or interface with the given string name?

A) getClass()
B) findClass()
C) Class.forName()
D) locateClass()

Answer:

C) Class.forName()

Explanation:

The Class.forName(String className) method in Java 17 can be used to obtain the Class object associated with the class or interface with the given string name.

39. Which of the following utility classes contains static methods for operating on objects, or returning them in a null-safe manner, available in Java 17?

A) Objects
B) Utils
C) ObjectUtils
D) SafeObjects

Answer:

A) Objects

Explanation:

The Objects class in Java 17 contains utility methods for operating on objects, such as comparing them, or returning them in a null-safe manner.


Practicing with these questions and understanding the detailed explanations will help you consolidate your knowledge and approach your Oracle Certified Professional: Java SE 17 Developer Certification with confidence. Continue exploring the intricacies of Java 17 and happy coding!

Leave a Comment

Your email address will not be published. Required fields are marked *

Scroll to Top