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Oracle 1z0-830 Exam Syllabus Topics:

SectionObjectives
Topic 1: Core APIs- Java standard library usage
  • 1. Streams and functional programming
    • 2. Collections Framework
      • 3. Date and Time API
        Topic 2: Database Connectivity (JDBC)- Database interaction
        • 1. JDBC API usage
          • 2. SQL execution and result handling
            Topic 3: Java Language Fundamentals- Java syntax and language structure
            • 1. Control flow statements
              • 2. Data types, variables, and operators
                Topic 4: Concurrency and Multithreading- Thread management
                • 1. Thread lifecycle and synchronization
                  • 2. Virtual threads and structured concurrency concepts
                    Topic 5: Input/Output and File Handling- NIO and file operations
                    • 1. File, Path, and Streams APIs
                      • 2. Serialization basics
                        Topic 6: Advanced Java Features (Java SE 21)- Modern language features
                        • 1. Records and record patterns
                          • 2. Virtual threads (Project Loom)
                            • 3. Sealed classes
                              • 4. Pattern matching for switch
                                Topic 7: Exception Handling and Debugging- Error handling mechanisms
                                • 1. Checked vs unchecked exceptions
                                  • 2. Try-with-resources
                                    Topic 8: Object-Oriented Programming- Core OOP principles
                                    • 1. Encapsulation, inheritance, polymorphism
                                      • 2. Abstract classes and interfaces

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                                        Oracle Java SE 21 Developer Professional Sample Questions (Q24-Q29):

                                        NEW QUESTION # 24
                                        Given:
                                        java
                                        double amount = 42_000.00;
                                        NumberFormat format = NumberFormat.getCompactNumberInstance(Locale.FRANCE, NumberFormat.Style.
                                        SHORT);
                                        System.out.println(format.format(amount));
                                        What is the output?

                                        Answer: B

                                        Explanation:
                                        In this code, a double variable amount is initialized to 42,000.00. The NumberFormat.
                                        getCompactNumberInstance(Locale.FRANCE, NumberFormat.Style.SHORT) method is used to obtain a compact number formatter for the French locale with the short style. The format method is then called to format the amount.
                                        The compact number formatting is designed to represent numbers in a shorter form, based on the patterns provided for a given locale. In the French locale, the short style represents thousands with a lowercase 'k'.
                                        Therefore, 42,000 is formatted as 42 k.
                                        * Option Evaluations:
                                        * A. 42000E: This format is not standard in the French locale for compact number formatting.
                                        * B. 42 000,00 €: This represents the number as a currency with two decimal places, which is not the compact form.
                                        * C. 42000: This is the plain number without any formatting, which does not match the compact number format.
                                        * D. 42 k: This is the correct compact representation of 42,000 in the French locale with the short style.
                                        Thus, option D (42 k) is the correct output.


                                        NEW QUESTION # 25
                                        Given:
                                        java
                                        Map<String, Integer> map = Map.of("b", 1, "a", 3, "c", 2);
                                        TreeMap<String, Integer> treeMap = new TreeMap<>(map);
                                        System.out.println(treeMap);
                                        What is the output of the given code fragment?

                                        Answer: C

                                        Explanation:
                                        In this code, a Map named map is created using Map.of with the following key-value pairs:
                                        * "b": 1
                                        * "a": 3
                                        * "c": 2
                                        The Map.of method returns an immutable map containing these mappings.
                                        Next, a TreeMap named treeMap is instantiated by passing the map to its constructor:
                                        java
                                        TreeMap<String, Integer> treeMap = new TreeMap<>(map);
                                        The TreeMap constructor with a Map parameter creates a new tree map containing the same mappings as the given map, ordered according to the natural ordering of its keys. In Java, the natural ordering for String keys is lexicographical order.
                                        Therefore, the TreeMap will store the entries in the following order:
                                        * "a": 3
                                        * "b": 1
                                        * "c": 2
                                        When System.out.println(treeMap); is executed, it outputs the TreeMap in its natural order, resulting in:
                                        r
                                        {a=3, b=1, c=2}
                                        Thus, the correct answer is option F: {a=3, b=1, c=2}.


                                        NEW QUESTION # 26
                                        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 # 27
                                        Which of the following methods of java.util.function.Predicate aredefault methods?

                                        Answer: B,D,E

                                        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 # 28
                                        Given:
                                        java
                                        try (FileOutputStream fos = new FileOutputStream("t.tmp");
                                        ObjectOutputStream oos = new ObjectOutputStream(fos)) {
                                        fos.write("Today");
                                        fos.writeObject("Today");
                                        oos.write("Today");
                                        oos.writeObject("Today");
                                        } catch (Exception ex) {
                                        // handle exception
                                        }
                                        Which statement compiles?

                                        Answer: A

                                        Explanation:
                                        In Java, FileOutputStream and ObjectOutputStream are used for writing data to files, but they have different purposes and methods. Let's analyze each statement:
                                        * fos.write("Today");
                                        The FileOutputStream class is designed to write raw byte streams to files. The write method in FileOutputStream expects a parameter of type int or byte[]. Since "Today" is a String, passing it directly to fos.
                                        write("Today"); will cause a compilation error because there is no write method in FileOutputStream that accepts a String parameter.
                                        * fos.writeObject("Today");
                                        The FileOutputStream class does not have a method named writeObject. The writeObject method is specific to ObjectOutputStream. Therefore, attempting to call fos.writeObject("Today"); will result in a compilation error.
                                        * oos.write("Today");
                                        The ObjectOutputStream class is used to write objects to an output stream. However, it does not have a write method that accepts a String parameter. The available write methods in ObjectOutputStream are for writing primitive data types and objects. Therefore, oos.write("Today"); will cause a compilation error.
                                        * oos.writeObject("Today");
                                        The ObjectOutputStream class provides the writeObject method, which is used to serialize objects and write them to the output stream. Since String implements the Serializable interface, "Today" can be serialized.
                                        Therefore, oos.writeObject("Today"); is valid and compiles successfully.
                                        In summary, the only statement that compiles without errors is oos.writeObject("Today");.
                                        References:
                                        * Java SE 21 & JDK 21 - ObjectOutputStream
                                        * Java SE 21 & JDK 21 - FileOutputStream


                                        NEW QUESTION # 29
                                        ......

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