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Oracle 1z0-830 Exam Syllabus Topics:

SectionObjectives
Java Language Fundamentals- Java syntax and language structure
  • 1. Control flow statements
    • 2. Data types, variables, and operators
      Concurrency and Multithreading- Thread management
      • 1. Thread lifecycle and synchronization
        • 2. Virtual threads and structured concurrency concepts
          Exception Handling and Debugging- Error handling mechanisms
          • 1. Checked vs unchecked exceptions
            • 2. Try-with-resources
              Core APIs- Java standard library usage
              • 1. Collections Framework
                • 2. Streams and functional programming
                  • 3. Date and Time API
                    Advanced Java Features (Java SE 21)- Modern language features
                    • 1. Records and record patterns
                      • 2. Sealed classes
                        • 3. Pattern matching for switch
                          • 4. Virtual threads (Project Loom)
                            Input/Output and File Handling- NIO and file operations
                            • 1. File, Path, and Streams APIs
                              • 2. Serialization basics
                                Object-Oriented Programming- Core OOP principles
                                • 1. Encapsulation, inheritance, polymorphism
                                  • 2. Abstract classes and interfaces
                                    Database Connectivity (JDBC)- Database interaction
                                    • 1. JDBC API usage
                                      • 2. SQL execution and result handling

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                                        Oracle Java SE 21 Developer Professional Sample Questions (Q75-Q80):

                                        NEW QUESTION # 75
                                        Given:
                                        java
                                        sealed class Vehicle permits Car, Bike {
                                        }
                                        non-sealed class Car extends Vehicle {
                                        }
                                        final class Bike extends Vehicle {
                                        }
                                        public class SealedClassTest {
                                        public static void main(String[] args) {
                                        Class<?> vehicleClass = Vehicle.class;
                                        Class<?> carClass = Car.class;
                                        Class<?> bikeClass = Bike.class;
                                        System.out.print("Is Vehicle sealed? " + vehicleClass.isSealed() +
                                        "; Is Car sealed? " + carClass.isSealed() +
                                        "; Is Bike sealed? " + bikeClass.isSealed());
                                        }
                                        }
                                        What is printed?

                                        Answer: D

                                        Explanation:
                                        * Understanding Sealed Classes in Java
                                        * Asealed classrestricts which other classes can extend it.
                                        * A sealed classmust explicitly declare its permitted subclassesusing the permits keyword.
                                        * Subclasses can be declared as:
                                        * sealed(restricts further extension).
                                        * non-sealed(removes the restriction, allowing unrestricted subclassing).
                                        * final(prevents further subclassing).
                                        * Analyzing the Given Code
                                        * Vehicle is declared as sealed with permits Car, Bike, meaning only Car and Bike can extend it.
                                        * Car is declared as non-sealed, which means itis no longer sealedand can have subclasses.
                                        * Bike is declared as final, meaningit cannot be subclassed.
                                        * Using isSealed() Method
                                        * vehicleClass.isSealed() #truebecause Vehicle is explicitly marked as sealed.
                                        * carClass.isSealed() #falsebecause Car is marked non-sealed.
                                        * bikeClass.isSealed() #falsebecause Bike is final, and a final class isnot considered sealed.
                                        * Final Output
                                        csharp
                                        Is Vehicle sealed? true; Is Car sealed? false; Is Bike sealed? false
                                        Thus, the correct answer is:"Is Vehicle sealed? true; Is Car sealed? false; Is Bike sealed? false" References:
                                        * Java SE 21 - Sealed Classes
                                        * Java SE 21 - isSealed() Method


                                        NEW QUESTION # 76
                                        Given:
                                        java
                                        int post = 5;
                                        int pre = 5;
                                        int postResult = post++ + 10;
                                        int preResult = ++pre + 10;
                                        System.out.println("postResult: " + postResult +
                                        ", preResult: " + preResult +
                                        ", Final value of post: " + post +
                                        ", Final value of pre: " + pre);
                                        What is printed?

                                        Answer: C

                                        Explanation:
                                        * Understanding post++ (Post-increment)
                                        * post++uses the value first, then increments it.
                                        * postResult = post++ + 10;
                                        * post starts as 5.
                                        * post++ returns 5, then post is incremented to 6.
                                        * postResult = 5 + 10 = 15.
                                        * Final value of post after this line is 6.
                                        * Understanding ++pre (Pre-increment)
                                        * ++preincrements the value first, then uses it.
                                        * preResult = ++pre + 10;
                                        * pre starts as 5.
                                        * ++pre increments pre to 6, then returns 6.
                                        * preResult = 6 + 10 = 16.
                                        * Final value of pre after this line is 6.
                                        Thus, the final output is:
                                        yaml
                                        postResult: 15, preResult: 16, Final value of post: 6, Final value of pre: 6 References:
                                        * Java SE 21 - Operators and Expressions
                                        * Java SE 21 - Arithmetic Operators


                                        NEW QUESTION # 77
                                        Given:
                                        java
                                        final Stream<String> strings =
                                        Files.readAllLines(Paths.get("orders.csv"));
                                        strings.skip(1)
                                        .limit(2)
                                        .forEach(System.out::println);
                                        And that the orders.csv file contains:
                                        mathematica
                                        OrderID,Customer,Product,Quantity,Price
                                        1,Kylian Mbappe,Keyboard,2,25.50
                                        2,Teddy Riner,Mouse,1,15.99
                                        3,Sebastien Loeb,Monitor,1,199.99
                                        4,Antoine Griezmann,Headset,3,45.00
                                        What is printed?

                                        Answer: A,C

                                        Explanation:
                                        1. Why Does Compilation Fail?
                                        * The error is in this line:
                                        java
                                        final Stream<String> strings = Files.readAllLines(Paths.get("orders.csv"));
                                        * Files.readAllLines(Paths.get("orders.csv")) returns a List<String>,not a Stream<String>.
                                        * A List<String> cannot be assigned to a Stream<String>.
                                        2. Correcting the Code
                                        * The correct way to create a stream from the file:
                                        java
                                        Stream<String> strings = Files.lines(Paths.get("orders.csv"));
                                        * This correctly creates a Stream<String> from the file.
                                        3. Expected Output After Fixing
                                        java
                                        Files.lines(Paths.get("orders.csv"))
                                        skip(1) // Skips the header row
                                        limit(2) // Limits to first two data rows
                                        forEach(System.out::println);
                                        * Output:
                                        arduino
                                        1,Kylian Mbappe,Keyboard,2,25.50
                                        2,Teddy Riner,Mouse,1,15.99
                                        Thus, the correct answer is:Compilation fails.
                                        References:
                                        * Java SE 21 - Files.readAllLines
                                        * Java SE 21 - Files.lines


                                        NEW QUESTION # 78
                                        What does the following code print?
                                        java
                                        import java.util.stream.Stream;
                                        public class StreamReduce {
                                        public static void main(String[] args) {
                                        Stream<String> stream = Stream.of("J", "a", "v", "a");
                                        System.out.print(stream.reduce(String::concat));
                                        }
                                        }

                                        Answer: D

                                        Explanation:
                                        In this code, a Stream of String elements is created containing the characters "J", "a", "v", and "a". The reduce method is then used with String::concat as the accumulator function.
                                        The reduce method with a single BinaryOperator parameter performs a reduction on the elements of the stream, using an associative accumulation function, and returns an Optional describing the reduced value, if any. In this case, it concatenates the strings in the stream.
                                        Since the stream contains elements, the reduction operation concatenates them to form the string "Java". The result is wrapped in an Optional, resulting in Optional[Java]. The print statement outputs this Optional object, displaying Optional[Java].


                                        NEW QUESTION # 79
                                        How would you create a ConcurrentHashMap configured to allow a maximum of 10 concurrent writer threads and an initial capacity of 42?
                                        Which of the following options meets this requirement?

                                        Answer: B

                                        Explanation:
                                        In Java, the ConcurrentHashMap class provides several constructors that allow for the customization of its initial capacity, load factor, and concurrency level. To configure a ConcurrentHashMap with an initial capacity of 42 and a concurrency level of 10, you can use the following constructor:
                                        java
                                        public ConcurrentHashMap(int initialCapacity, float loadFactor, int concurrencyLevel) Parameters:
                                        * initialCapacity: The initial capacity of the hash table. This is the number of buckets that the hash table will have when it is created. In this case, it is set to 42.
                                        * loadFactor: A measure of how full the hash table is allowed to get before it is resized. The default value is 0.75, but in this case, it is set to 0.88.
                                        * concurrencyLevel: The estimated number of concurrently updating threads. This is used as a hint for internal sizing. In this case, it is set to 10.
                                        Therefore, to create a ConcurrentHashMap with an initial capacity of 42, a load factor of 0.88, and a concurrency level of 10, you can use the following code:
                                        java
                                        var concurrentHashMap = new ConcurrentHashMap<>(42, 0.88f, 10);
                                        Option Evaluations:
                                        * A. var concurrentHashMap = new ConcurrentHashMap(42);: This constructor sets the initial capacity to 42 but uses the default load factor (0.75) and concurrency level (16). It does not meet the requirement of setting the concurrency level to 10.
                                        * B. None of the suggestions.: This is incorrect because option E provides the correct configuration.
                                        * C. var concurrentHashMap = new ConcurrentHashMap();: This uses the default constructor, which sets the initial capacity to 16, the load factor to 0.75, and the concurrency level to 16. It does not meet the specified requirements.
                                        * D. var concurrentHashMap = new ConcurrentHashMap(42, 10);: This constructor sets the initial capacity to 42 and the load factor to 10, which is incorrect because the load factor should be a float value between 0 and 1.
                                        * E. var concurrentHashMap = new ConcurrentHashMap(42, 0.88f, 10);: This correctly sets the initial capacity to 42, the load factor to 0.88, and the concurrency level to 10, meeting all the specified requirements.
                                        Therefore, the correct answer is option E.


                                        NEW QUESTION # 80
                                        ......

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