OOPJ Quiz

In the context of encapsulation, what is the primary purpose of using private instance variables with public getter and setter methods in a Java class?

• To allow unrestricted access to the class’s internal data

• To ensure that the class can only be instantiated within the same package

• To hide the internal state of the object and provide controlled access to it

• To enable automatic memory management by the JVM

When a Java program is compiled, the JVM generates bytecode. What happens if a .class file is executed on a machine with a different architecture than the one it was compiled on?

• The program will fail to execute due to architecture mismatch

• The JVM interprets the bytecode, making it platform-independent

• The bytecode is recompiled into native code specific to the new architecture

• The JRE throws a ClassFormatError at runtime

Consider a class with a static initialization block that initializes a static array. If an exception occurs in the static block during class loading, what will happen?

• The exception is caught automatically by the JVM, and the class is loaded

• The class loading fails, and a ExceptionInInitializerError is thrown

• The static block is skipped, and the array remains uninitialized

• The program continues execution but skips the static array initialization

In a multilevel inheritance hierarchy, a subclass overrides a method from its parent class. If the parent class method is declared with the final keyword, what is the outcome?

• The method can be overridden only if the subclass is in the same package

  Correct Answer: B

• The method is overridden, but the final keyword is ignored in the subclass

• The subclass can override the method, but it must also mark it as final

• The subclass cannot override the method, and a compile-time error occurs

A Java interface defines a default method, and a class implementing this interface provides its own implementation of the same method. Which implementation is invoked when the method is called on an instance of the class?

• The interface’s default method is always invoked

• The method invocation depends on the access modifier of the class’s method

• The class’s implementation overrides the default method

• A runtime exception is thrown due to method conflict

In a try-catch block, a finally block contains a return statement. If both the try block and the catch block also contain return statements, which return value takes precedence?

• The return value from the finally block

• The return value from the try block

• The return value from the catch block

• A NullPointerException is thrown

When using a StringBuilder to modify a string, what happens to the original string if the StringBuilder was initialized with a String object?

• The original String object is modified in the string pool

• The StringBuilder modifies the string pool, causing a runtime error

• The original String is garbage collected immediately

• The original String remains unchanged, and StringBuilder operates on a separate copy

When reading a file using FileInputStream, the read() method returns an integer value. What does a return value of -1 signify?

• The end of the file has been reached

• An I/O error occurred during the read operation

• The file is empty and contains no bytes

• The stream is closed and cannot be read

Two threads are accessing a synchronized method in a class. If one thread is in a wait() state within the method, what must happen for the thread to resume execution?

• The thread automatically resumes after a fixed time interval

• The thread must be interrupted using the interrupt() method

• The JVM schedules the thread to resume when the CPU is available

• Another thread must call notify() or notifyAll() on the same object

When using a PreparedStatement to execute a parameterized SQL query, what is the primary benefit of binding parameters instead of concatenating strings in the query?

• It reduces the memory footprint of the query execution

• It prevents SQL injection attacks by properly escaping user input

• It allows the query to be executed without a database connection

• It automatically optimizes the query for faster execution