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Oracle 1z0-830 Exam Syllabus Topics:

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

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                                        Oracle Java SE 21 Developer Professional Sample Questions (Q79-Q84):

                                        NEW QUESTION # 79
                                        Given:
                                        java
                                        StringBuffer us = new StringBuffer("US");
                                        StringBuffer uk = new StringBuffer("UK");
                                        Stream<StringBuffer> stream = Stream.of(us, uk);
                                        String output = stream.collect(Collectors.joining("-", "=", ""));
                                        System.out.println(output);
                                        What is the given code fragment's output?

                                        Answer: F

                                        Explanation:
                                        In this code, two StringBuffer objects, us and uk, are created with the values "US" and "UK", respectively. A stream is then created from these objects using Stream.of(us, uk).
                                        The collect method is used with Collectors.joining("-", "=", ""). The joining collector concatenates the elements of the stream into a single String with the following parameters:
                                        * Delimiter ("-"):Inserted between each element.
                                        * Prefix ("="):Inserted at the beginning of the result.
                                        * Suffix (""):Inserted at the end of the result.
                                        Therefore, the elements "US" and "UK" are concatenated with "-" between them, resulting in "US-UK". The prefix "=" is added at the beginning, resulting in the final output =US-UK.


                                        NEW QUESTION # 80
                                        Given:
                                        java
                                        Period p = Period.between(
                                        LocalDate.of(2023, Month.MAY, 4),
                                        LocalDate.of(2024, Month.MAY, 4));
                                        System.out.println(p);
                                        Duration d = Duration.between(
                                        LocalDate.of(2023, Month.MAY, 4),
                                        LocalDate.of(2024, Month.MAY, 4));
                                        System.out.println(d);
                                        What is the output?

                                        Answer: C

                                        Explanation:
                                        In this code, two LocalDate instances are created representing May 4, 2023, and May 4, 2024. The Period.
                                        between() method is used to calculate the period between these two dates, and the Duration.between() method is used to calculate the duration between them.
                                        Period Calculation:
                                        The Period.between() method calculates the amount of time between two LocalDate objects in terms of years, months, and days. In this case, the period between May 4, 2023, and May 4, 2024, is exactly one year.
                                        Therefore, p is P1Y, which stands for a period of one year. Printing p will output P1Y.
                                        Duration Calculation:
                                        The Duration.between() method is intended to calculate the duration between two temporal objects that have time components, such as LocalDateTime or Instant. However, LocalDate represents a date without a time component. Attempting to use Duration.between() with LocalDate instances will result in an UnsupportedTemporalTypeException because Duration requires time-based units, which LocalDate does not support.
                                        Exception Details:
                                        The UnsupportedTemporalTypeException is thrown when an unsupported unit is used. In this case, Duration.
                                        between() internally attempts to access time-based fields (like seconds), which are not supported by LocalDate. This behavior is documented in the Java Bug System underJDK-8170275.
                                        Correct Usage:
                                        To calculate the duration between two dates, including time components, you should use LocalDateTime or Instant. For example:
                                        java
                                        LocalDateTime start = LocalDateTime.of(2023, Month.MAY, 4, 0, 0);
                                        LocalDateTime end = LocalDateTime.of(2024, Month.MAY, 4, 0, 0);
                                        Duration d = Duration.between(start, end);
                                        System.out.println(d); // Outputs: PT8784H
                                        This will correctly calculate the duration as PT8784H, representing 8,784 hours (which is 366 days, accounting for a leap year).
                                        Conclusion:
                                        The output of the given code will be:
                                        pgsql
                                        P1Y
                                        Exception in thread "main" java.time.temporal.UnsupportedTemporalTypeException: Unsupported unit:
                                        Seconds
                                        Therefore, the correct answer is D:
                                        nginx
                                        P1Y
                                        UnsupportedTemporalTypeException


                                        NEW QUESTION # 81
                                        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: B

                                        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 # 82
                                        Given:
                                        java
                                        List<String> abc = List.of("a", "b", "c");
                                        abc.stream()
                                        .forEach(x -> {
                                        x = x.toUpperCase();
                                        });
                                        abc.stream()
                                        .forEach(System.out::print);
                                        What is the output?

                                        Answer: C

                                        Explanation:
                                        In the provided code, a list abc is created containing the strings "a", "b", and "c". The first forEach operation attempts to convert each element to uppercase by assigning x = x.toUpperCase();. However, this assignment only changes the local variable x within the lambda expression and does not modify the elements in the original list abc. Strings in Java are immutable, meaning their values cannot be changed once created.
                                        Therefore, the original list remains unchanged.
                                        The second forEach operation iterates over the original list and prints each element. Since the list was not modified, the output will be the concatenation of the original elements: abc.
                                        To achieve the output ABC, you would need to collect the transformed elements into a new list, as shown below:
                                        java
                                        List<String> abc = List.of("a", "b", "c");
                                        List<String> upperCaseAbc = abc.stream()
                                        map(String::toUpperCase)
                                        collect(Collectors.toList());
                                        upperCaseAbc.forEach(System.out::print);
                                        In this corrected version, the map operation creates a new stream with the uppercase versions of the original elements, which are then collected into a new list upperCaseAbc. The forEach operation then prints ABC.


                                        NEW QUESTION # 83
                                        Given:
                                        java
                                        StringBuilder result = Stream.of("a", "b")
                                        .collect(
                                        () -> new StringBuilder("c"),
                                        StringBuilder::append,
                                        (a, b) -> b.append(a)
                                        );
                                        System.out.println(result);
                                        What is the output of the given code fragment?

                                        Answer: C

                                        Explanation:
                                        In this code, a Stream containing the elements "a" and "b" is processed using the collect method. The collect method is a terminal operation that performs a mutable reduction on the elements of the stream using a Collector. In this case, custom implementations for the supplier, accumulator, and combiner are provided.
                                        Components of the collect Method:
                                        * Supplier:
                                        * () -> new StringBuilder("c")
                                        * This supplier creates a new StringBuilder initialized with the string "c".
                                        * Accumulator:
                                        * StringBuilder::append
                                        * This accumulator appends each element of the stream to the StringBuilder.
                                        * Combiner:
                                        * (a, b) -> b.append(a)
                                        * This combiner is used in parallel stream operations to merge two StringBuilder instances. It appends the contents of a to b.
                                        Execution Flow:
                                        * Stream Elements:"a", "b"
                                        * Initial StringBuilder:"c"
                                        * Accumulation:
                                        * The first element "a" is appended to "c", resulting in "ca".
                                        * The second element "b" is appended to "ca", resulting in "cab".
                                        * Combiner:
                                        * In this sequential stream, the combiner is not utilized. The combiner is primarily used in parallel streams to merge partial results.
                                        Final Result:
                                        The StringBuilder contains "cab". Therefore, the output of the program is:
                                        nginx
                                        cab


                                        NEW QUESTION # 84
                                        ......

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