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| Section | Objectives |
|---|---|
| Java Language Fundamentals | - Java syntax and language structure
|
| Database Connectivity (JDBC) | - Database interaction
|
| Concurrency and Multithreading | - Thread management
|
| Core APIs | - Java standard library usage
|
| Object-Oriented Programming | - Core OOP principles
|
| Input/Output and File Handling | - NIO and file operations
|
| Advanced Java Features (Java SE 21) | - Modern language features
|
| Exception Handling and Debugging | - Error handling mechanisms
|
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NEW QUESTION # 18
Given:
java
Integer frenchRevolution = 1789;
Object o1 = new String("1789");
Object o2 = frenchRevolution;
frenchRevolution = null;
Object o3 = o2.toString();
System.out.println(o1.equals(o3));
What is printed?
Answer: B
Explanation:
* Understanding Variable Assignments
java
Integer frenchRevolution = 1789;
Object o1 = new String("1789");
Object o2 = frenchRevolution;
frenchRevolution = null;
* frenchRevolution is an Integer with value1789.
* o1 is aString with value "1789".
* o2 storesa reference to frenchRevolution, which is an Integer (1789).
* frenchRevolution = null;only nullifies the reference, but o2 still holds the Integer 1789.
* Calling toString() on o2
java
Object o3 = o2.toString();
* o2 refers to an Integer (1789).
* Integer.toString() returns theString representation "1789".
* o3 is assigned "1789" (String).
* Evaluating o1.equals(o3)
java
System.out.println(o1.equals(o3));
* o1.equals(o3) isequivalent to:
java
"1789".equals("1789")
* Since both areequal strings, the output is:
arduino
true
Thus, the correct answer is:true
References:
* Java SE 21 - Integer.toString()
* Java SE 21 - String.equals()
NEW QUESTION # 19
Which of the following statements is correct about a final class?
Answer: C
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 # 20
What do the following print?
java
public class Main {
int instanceVar = staticVar;
static int staticVar = 666;
public static void main(String args[]) {
System.out.printf("%d %d", new Main().instanceVar, staticVar);
}
static {
staticVar = 42;
}
}
Answer: D
Explanation:
In this code, the class Main contains both an instance variable instanceVar and a static variable staticVar. The sequence of initialization and execution is as follows:
* Static Variable Initialization:
* staticVar is declared and initialized to 666.
* Static Block Execution:
* The static block executes, updating staticVar to 42.
* Instance Variable Initialization:
* When a new instance of Main is created, instanceVar is initialized to the current value of staticVar, which is 42.
* main Method Execution:
* The main method creates a new instance of Main and prints the values of instanceVar and staticVar.
Therefore, the output of the program is 42 42.
NEW QUESTION # 21
Which of the following methods of java.util.function.Predicate aredefault methods?
Answer: A,B,C
Explanation:
* Understanding java.util.function.Predicate<T>
* The Predicate<T> interface represents a function thattakes an input and returns a boolean(true or false).
* It is often used for filtering operations in functional programming and streams.
* Analyzing the Methods:
* and(Predicate<? super T> other)#Default method
* Combines two predicates usinglogical AND(&&).
java
Predicate<String> startsWithA = s -> s.startsWith("A");
Predicate<String> hasLength3 = s -> s.length() == 3;
Predicate<String> combined = startsWithA.and(hasLength3);
* #isEqual(Object targetRef)#Static method
* Not a default method, because it doesnot operate on an instance.
java
Predicate<String> isEqualToHello = Predicate.isEqual("Hello");
* negate()#Default method
* Negates a predicate (! operator).
java
Predicate<String> notEmpty = s -> !s.isEmpty();
Predicate<String> isEmpty = notEmpty.negate();
* #not(Predicate<? super T> target)#Static method (introduced in Java 11)
* Not a default method, since it is static.
* or(Predicate<? super T> other)#Default method
* Combines two predicates usinglogical OR(||).
* #test(T t)#Abstract method
* Not a default method, because every predicatemust implement this method.
Thus, the correct answers are:and(Predicate<? super T> other), negate(), or(Predicate<? super T> other) References:
* Java SE 21 - Predicate Interface
* Java SE 21 - Functional Interfaces
NEW QUESTION # 22
Given:
java
package vehicule.parent;
public class Car {
protected String brand = "Peugeot";
}
and
java
package vehicule.child;
import vehicule.parent.Car;
public class MiniVan extends Car {
public static void main(String[] args) {
Car car = new Car();
car.brand = "Peugeot 807";
System.out.println(car.brand);
}
}
What is printed?
Answer: C
Explanation:
In Java,protected memberscan only be accessedwithin the same packageor bysubclasses, but there is a key restriction:
* A protected member of a superclass is only accessible through inheritance in a subclass but not through an instance of the superclass that is declared outside the package.
Why does compilation fail?
In the MiniVan class, the following line causes acompilation error:
java
Car car = new Car();
car.brand = "Peugeot 807";
* The brand field isprotectedin Car, which means it isnot accessible via an instance of Car outside the vehicule.parent package.
* Even though MiniVan extends Car, itcannotaccess brand using a Car instance (car.brand) because car is declared as an instance of Car, not MiniVan.
* The correct way to access brand inside MiniVan is through inheritance (this.brand or super.brand).
Corrected Code
If we change the MiniVan class like this, it will compile and run successfully:
java
package vehicule.child;
import vehicule.parent.Car;
public class MiniVan extends Car {
public static void main(String[] args) {
MiniVan minivan = new MiniVan(); // Access via inheritance
minivan.brand = "Peugeot 807";
System.out.println(minivan.brand);
}
}
This would output:
nginx
Peugeot 807
Key Rule from Oracle Java Documentation
* Protected membersof a class are accessible withinthe same packageand tosubclasses, butonly through inheritance, not through a superclass instance declared outside the package.
References:
* Java SE 21 & JDK 21 - Controlling Access to Members of a Class
* Java SE 21 & JDK 21 - Inheritance Rules
NEW QUESTION # 23
......
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