1z0-830 Exam Questions - Java SE 21 Developer Professional Test Questions & 1z0-830 Test Guide

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

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                                        Oracle Java SE 21 Developer Professional Sample Questions (Q28-Q33):

                                        NEW QUESTION # 28
                                        Which two of the following aren't the correct ways to create a Stream?

                                        Answer: D,E


                                        NEW QUESTION # 29
                                        Given:
                                        java
                                        public class Test {
                                        class A {
                                        }
                                        static class B {
                                        }
                                        public static void main(String[] args) {
                                        // Insert here
                                        }
                                        }
                                        Which three of the following are valid statements when inserted into the given program?

                                        Answer: B,D,E

                                        Explanation:
                                        In the provided code, we have two inner classes within the Test class:
                                        * Class A:
                                        * An inner (non-static) class.
                                        * Instances of A are associated with an instance of the enclosing Test class.
                                        * Class B:
                                        * A static nested class.
                                        * Instances of B are not associated with any instance of the enclosing Test class and can be instantiated without an instance of Test.
                                        Evaluation of Statements:
                                        A: A a = new A();
                                        * Invalid.Since A is a non-static inner class, it requires an instance of the enclosing class Test to be instantiated. Attempting to instantiate A without an instance of Test will result in a compilation error.
                                        B: B b = new Test.B();
                                        * Valid.B is a static nested class and can be instantiated without an instance of Test. This syntax is correct.
                                        C: A a = new Test.A();
                                        * Invalid.Even though A is referenced through Test, it is a non-static inner class and requires an instance of Test for instantiation. This will result in a compilation error.
                                        D: B b = new Test().new B();
                                        * Invalid.While this syntax is used for instantiating non-static inner classes, B is a static nested class and does not require an instance of Test. This will result in a compilation error.
                                        E: B b = new B();
                                        * Valid.Since B is a static nested class, it can be instantiated directly without referencing the enclosing class.
                                        F: A a = new Test().new A();
                                        * Valid.This is the correct syntax for instantiating a non-static inner class. An instance of Test is created, and then an instance of A is created associated with that Test instance.
                                        Therefore, the valid statements are B, E, and F.


                                        NEW QUESTION # 30
                                        What do the following print?
                                        java
                                        import java.time.Duration;
                                        public class DividedDuration {
                                        public static void main(String[] args) {
                                        var day = Duration.ofDays(2);
                                        System.out.print(day.dividedBy(8));
                                        }
                                        }

                                        Answer: E

                                        Explanation:
                                        In this code, a Duration object day is created representing a duration of 2 days using the Duration.ofDays(2) method. The dividedBy(long divisor) method is then called on this Duration object with the argument 8.
                                        The dividedBy(long divisor) method returns a copy of the original Duration divided by the specified value. In this case, dividing 2 days by 8 results in a duration of 0.25 days. In the ISO-8601 duration format used by Java's Duration class, this is represented as PT6H, which stands for a period of 6 hours.
                                        Therefore, the output of the System.out.print statement is PT6H.


                                        NEW QUESTION # 31
                                        Which of the following isn't a valid option of the jdeps command?

                                        Answer: A

                                        Explanation:
                                        The jdeps tool is a Java class dependency analyzer that can be used to understand the static dependencies of applications and libraries. It provides several command-line options to customize its behavior.
                                        Valid jdeps Options:
                                        * --generate-open-module: Generates a module declaration (module-info.java) with open directives for the given JAR files or classes.
                                        * --list-deps: Lists the immediate dependencies of the specified classes or JAR files.
                                        * --generate-module-info: Generates a module declaration (module-info.java) for the given JAR files or classes.
                                        * --print-module-deps: Prints the module dependencies of the specified modules or JAR files.
                                        * --list-reduced-deps: Lists the reduced dependencies, showing only the packages that are directly depended upon.
                                        Invalid Option:
                                        * --check-deps: There is no --check-deps option in the jdeps tool.
                                        Conclusion:
                                        Option A (--check-deps) is not a valid option of the jdeps command.


                                        NEW QUESTION # 32
                                        Given:
                                        java
                                        public class SpecialAddition extends Addition implements Special {
                                        public static void main(String[] args) {
                                        System.out.println(new SpecialAddition().add());
                                        }
                                        int add() {
                                        return --foo + bar--;
                                        }
                                        }
                                        class Addition {
                                        int foo = 1;
                                        }
                                        interface Special {
                                        int bar = 1;
                                        }
                                        What is printed?

                                        Answer: C

                                        Explanation:
                                        1. Why does the compilation fail?
                                        * The interface Special contains bar as int bar = 1;.
                                        * In Java, all interface fields are implicitly public, static, and final.
                                        * This means that bar is a constant (final variable).
                                        * The method add() contains bar--, which attempts to modify bar.
                                        * Since bar is final, it cannot be modified, causing acompilation error.
                                        2. Correcting the Code
                                        To make the code compile, bar must not be final. One way to fix this:
                                        java
                                        class SpecialImpl implements Special {
                                        int bar = 1;
                                        }
                                        Or modify the add() method:
                                        java
                                        int add() {
                                        return --foo + bar; // No modification of bar
                                        }
                                        Thus, the correct answer is:Compilation fails.
                                        References:
                                        * Java SE 21 - Interfaces
                                        * Java SE 21 - Final Variables


                                        NEW QUESTION # 33
                                        ......

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