Hey there! Welcome to our latest blog post, where we’ve put together a practice test for the Oracle Certified Professional: Java SE 17 Developer exam. It’s like a mock exam to help you prepare and feel confident!
This test is all about Java SE 17, the latest version of Java. It covers everything from basic programming concepts to advanced Java features. If you’re looking to prove your skills in Java and earn that professional certification, this practice test is perfect for you.
Dive into our practice test to see where you stand and what you need to brush up on. It’s a great way to prepare and boost your chances of acing the real exam. Let’s get started and move one step closer to becoming a Java SE 17 Developer pro!
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?
Answer:
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?
Answer:
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?
Answer:
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?
Answer:
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)?
Answer:
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?
Answer:
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?
Answer:
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?
Answer:
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?
Answer:
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?
Answer:
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?
Answer:
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?
Answer:
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?
Answer:
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?
Answer:
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?
Answer:
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?
Answer:
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?
Answer:
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?
Answer:
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?
Answer:
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?
Answer:
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?
Answer:
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?
Answer:
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?
Answer:
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?
Answer:
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?
Answer:
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?
Answer:
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?
Answer:
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?
Answer:
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?
Answer:
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?
Answer:
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?
Answer:
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?
Answer:
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?
Answer:
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?
Answer:
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?
Answer:
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?
Answer:
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?
Answer:
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?
Answer:
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?
Answer:
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!