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| Section | Objectives |
|---|---|
| Topic 1: Exception Handling | - Use try-with-resources - Create custom exceptions - Handle checked and unchecked exceptions |
| Topic 2: Java I/O and NIO | - Use Path, Files, and related APIs - Read and write files - Process file system resources |
| Topic 3: Functional Programming | - Process data using Stream API - Work with functional interfaces - Use lambda expressions and method references |
| Topic 4: Java Concurrency | - Work with concurrent collections and executors - Use virtual threads - Create and manage threads |
| Topic 5: Handling Date, Time, Text, Numeric and Boolean Values | - Use String, StringBuilder, and related APIs - Use date, time, duration, period, and localization APIs - Work with primitive wrappers and number formatting |
| Topic 6: Object-Oriented Programming | - Implement encapsulation and abstraction - Apply inheritance and polymorphism - Create and use classes, interfaces, enums, and records |
| Topic 7: Annotations and JDBC | - Execute SQL operations and process results - Use built-in and custom annotations - Connect to databases using JDBC |
| Topic 8: Modules and Packaging | - Manage dependencies and exports - Package and deploy applications - Create and use Java modules |
| Topic 9: Collections and Generics | - Apply generics and bounded types - Use List, Set, Map, Queue, and Deque implementations - Use sequenced collections and maps |
| Topic 10: Controlling Program Flow | - Work with records and sealed classes - Use switch expressions and pattern matching - Apply decision statements and loops |
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NEW QUESTION # 41
Consider the following methods to load an implementation of MyService using ServiceLoader. Which of the methods are correct? (Choose all that apply)
Answer: B,C
Explanation:
The ServiceLoader class in Java is used to load service providers implementing a given service interface. The following methods are evaluated for their correctness in loading an implementation of MyService:
* A. MyService service = ServiceLoader.load(MyService.class).iterator().next(); This method uses the ServiceLoader.load(MyService.class) to create a ServiceLoader instance for MyService.
Calling iterator().next() retrieves the next available service provider. If no providers are available, a NoSuchElementException will be thrown. This approach is correct but requires handling the potential exception if no providers are found.
* B. MyService service = ServiceLoader.load(MyService.class).findFirst().get(); This method utilizes the findFirst() method introduced in Java 9, which returns an Optional describing the first available service provider. Calling get() on the Optional retrieves the service provider if present; otherwise, a NoSuchElementException is thrown. This approach is correct and provides a more concise way to obtain the first service provider.
* C. MyService service = ServiceLoader.getService(MyService.class);
The ServiceLoader class does not have a method named getService. Therefore, this method is incorrect and will result in a compilation error.
* D. MyService service = ServiceLoader.services(MyService.class).getFirstInstance(); The ServiceLoader class does not have a method named services or getFirstInstance. Therefore, this method is incorrect and will result in a compilation error.
In summary, options A and B are correct methods to load an implementation of MyService using ServiceLoader.
NEW QUESTION # 42
What do the following print?
java
public class DefaultAndStaticMethods {
public static void main(String[] args) {
WithStaticMethod.print();
}
}
interface WithDefaultMethod {
default void print() {
System.out.print("default");
}
}
interface WithStaticMethod extends WithDefaultMethod {
static void print() {
System.out.print("static");
}
}
Answer: A
Explanation:
In this code, we have two interfaces and a class with a main method:
* WithDefaultMethod Interface:
* Declares a default method print() that outputs "default".
* WithStaticMethod Interface:
* Extends WithDefaultMethod.
* Declares a static method print() that outputs "static".
* DefaultAndStaticMethods Class:
* Contains the main method, which calls WithStaticMethod.print().
Key Points:
* Static Methods in Interfaces:
* Static methods in interfaces are not inherited by implementing or extending classes or interfaces.
They belong solely to the interface in which they are declared.
* Default Methods in Interfaces:
* Default methods can be inherited by implementing classes, but they cannot be overridden by static methods in subinterfaces.
Execution Flow:
* The main method calls WithStaticMethod.print().
* This invokes the static method print() defined in the WithStaticMethod interface, which outputs "static".
Therefore, the program compiles successfully and prints static.
NEW QUESTION # 43
Given:
java
var hauteCouture = new String[]{ "Chanel", "Dior", "Louis Vuitton" };
var i = 0;
do {
System.out.print(hauteCouture[i] + " ");
} while (i++ > 0);
What is printed?
Answer: C
Explanation:
* Understanding the do-while Loop
* The do-while loopexecutes at least oncebefore checking the condition.
* The condition i++ > 0 increments iafterchecking.
* Step-by-Step Execution
* Iteration 1:
* i = 0
* Prints: "Chanel"
* i++ updates i to 1
* Condition 1 > 0is true, so the loop exits.
* Why Doesn't the Loop Continue?
* Since i starts at 0, the conditioni++ > 0 is false after the first iteration.
* The loopexits immediately after printing "Chanel".
* Final Output
nginx
Chanel
Thus, the correct answer is:Chanel
References:
* Java SE 21 - do-while Loop
* Java SE 21 - Post-Increment Behavior
NEW QUESTION # 44
Which of the following suggestions compile?(Choose two.)
Answer: B,C
Explanation:
Option A (sealed class Figure permits Rectangle {} and final class Rectangle extends Figure {}) - Valid
* Why it compiles?
* Figure issealed, meaning itmust explicitly declareits subclasses.
* Rectangle ispermittedto extend Figure and isdeclared final, meaning itcannot be extended further.
* This followsvalid sealed class rules.
Option B (sealed class Figure permits Rectangle {} and public class Rectangle extends Figure {}) -# Invalid
* Why it fails?
* Rectangle extends Figure, but it doesnot specify if it is sealed, final, or non-sealed.
* Fix:The correct declaration must be one of the following:
java
final class Rectangle extends Figure {} // OR
sealed class Rectangle permits OtherClass {} // OR
non-sealed class Rectangle extends Figure {}
Option C (final sealed class Circle extends Figure {}) -#Invalid
* Why it fails?
* A class cannot be both final and sealedat the same time.
* sealed meansit must have permitted subclasses, but final meansit cannot be extended.
* Fix:Change final sealed to just final:
java
final class Circle extends Figure {}
Option D (public sealed class Figure permits Circle, Rectangle {} with final class Circle and non-sealed class Rectangle) - Valid
* Why it compiles?
* Figure issealed, meaning it mustdeclare its permitted subclasses(Circle and Rectangle).
* Circle is declaredfinal, so itcannot have subclasses.
* Rectangle is declarednon-sealed, meaningit can be subclassedfreely.
* This correctly followsJava's sealed class rules.
Thus, the correct answers are:A, D
References:
* Java SE 21 - Sealed Classes
* Java SE 21 - Class Modifiers
NEW QUESTION # 45
Which of the following statements is correct about a final class?
Answer: E
Explanation:
In Java, the final keyword can be applied to classes, methods, and variables to impose certain restrictions.
Final Classes:
* Definition:A class declared with the final keyword is known as a final class.
* Purpose:Declaring a class as final prevents it from being subclassed. This is useful when you want to ensure that the class's implementation remains unchanged and cannot be extended or modified through inheritance.
Option Evaluations:
* A. The final keyword in its declaration must go right before the class keyword.
* This is correct. The syntax for declaring a final class is:
java
public final class ClassName {
// class body
}
* However, this statement is about syntax rather than the core characteristic of a final class.
* B. It must contain at least a final method.
* Incorrect. A final class can have zero or more methods, and none of them are required to be declared as final. The final keyword at the class level prevents inheritance, regardless of the methods' finality.
* C. It cannot be extended by any other class.
* Correct. The primary characteristic of a final class is that it cannot be subclassed. Attempting to do so will result in a compilation error.
* D. It cannot implement any interface.
* Incorrect. A final class can implement interfaces. Declaring a class as final restricts inheritance but does not prevent the class from implementing interfaces.
* E. It cannot extend another class.
* Incorrect. A final class can extend another class. The final keyword prevents the class from being subclassed but does not prevent it from being a subclass itself.
Therefore, the correct statement about a final class is option C: "It cannot be extended by any other class."
NEW QUESTION # 46
......
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