What is the initial capacity of the HashMap when no size is defined, and how is it related to the number of entries it can ideally accommodate without resizing?
- 16, and it can accommodate 16 entries.
- 10, and it can accommodate 10 entries.
- 32, and it can accommodate 32 entries.
- The initial capacity is not defined, and it dynamically adjusts as entries are added.
In Java, when you create a HashMap without specifying an initial capacity, it defaults to an initial capacity of 16. This means that initially, the HashMap can accommodate 16 key-value pairs. However, as the number of entries increases and reaches a certain threshold (usually 75% of the capacity), the HashMap automatically resizes itself, doubling its capacity. So, option (a) is correct, with the explanation that it can ideally accommodate 16 entries initially but will resize when necessary.
What will be the output of calling a method overridden in the child class?
- It depends on how the method is called
- It depends on the method's signature
- The child class's method will always be called
- The parent class's method will always be called
When a method is overridden in the child class, the version of the method in the child class is called when the method is invoked on an instance of the child class. This is known as method overriding and is a fundamental concept in object-oriented programming.
In a multithreaded application where multiple threads are reading and writing to a shared User object, how would you ensure that the read and write operations are thread-safe?
- Ensure that all threads run in a single thread by using a single-core CPU.
- Implement a ReadWriteLock to control access to the User object.
- Use synchronized methods for read and write operations on the User object.
- Use the volatile keyword for the User object.
To ensure thread safety in a multithreaded application, you can use synchronized methods for read and write operations on the shared User object. This prevents multiple threads from accessing and modifying the object simultaneously, avoiding data corruption and race conditions. The other options do not provide effective thread safety mechanisms.
The ______ method of the Lock interface is used to acquire the lock.
- acquire()
- lock()
- tryLock()
- unlock()
The lock() method of the Lock interface is used to acquire the lock. It blocks until the lock is available and then acquires it. The unlock() method is used to release the lock. The acquire() and tryLock() methods are not part of the standard Lock interface in Java.
Consider a scenario where you have a large number of short-lived asynchronous tasks. Which type of ExecutorService would you consider using and why?
- CachedThreadPoolExecutor: A thread pool that dynamically creates and recycles threads.
- FixedThreadPoolExecutor: A fixed-size thread pool with a specific number of threads.
- ScheduledThreadPoolExecutor: A thread pool for scheduling tasks at a fixed rate or delay.
- SingleThreadPoolExecutor: A single-threaded ExecutorService.
In this scenario, the CachedThreadPoolExecutor is suitable. It dynamically adjusts the number of threads based on the workload, making it efficient for short-lived tasks. SingleThreadPoolExecutor and FixedThreadPoolExecutor have limitations for such cases, and ScheduledThreadPoolExecutor is designed for scheduling tasks, not managing short-lived tasks.
The ________ interface is used to execute SQL stored procedures.
- CallableStatement
- Connection
- PreparedStatement
- Statement
In JDBC, the CallableStatement interface is used to execute SQL stored procedures. It allows you to call stored procedures that may take parameters and return values. Statement is used for executing regular SQL statements, Connection is used for establishing database connections, and PreparedStatement is used for executing parameterized SQL queries.
The ________ data type in Java can store decimal numbers up to 15 decimal places.
- BigDecimal
- double
- float
- long
In Java, the BigDecimal data type is used to store decimal numbers with precision up to 15 decimal places. It is commonly used in financial and scientific applications where high precision is required. The float and double types have limited precision and are not suitable for this purpose.
Lambda expressions eliminate the need for ________.
- Anonymous inner classes
- Arrays
- Inheritance
- Interfaces
Lambda expressions eliminate the need for anonymous inner classes. Before lambda expressions were introduced in Java, anonymous inner classes were used to implement single-method interfaces, like Runnable or ActionListener. Lambda expressions provide a more concise and expressive way to define such implementations, reducing the verbosity of code.
How does the compiler resolve the "+" operator when used with different data types (e.g., String and int)?
- It performs the operation based on the type of the first operand and ignores the second operand's type.
- It throws a compilation error because the + operator cannot be used with different data types.
- It throws a runtime error because the + operator is ambiguous with different data types.
- It uses type conversion to promote one of the operands to the type of the other operand, and then performs the operation.
It uses type conversion to promote one of the operands to the type of the other operand, and then performs the operation. For example, if you add a string and an int, the int is converted to a string, and string concatenation is performed. If you add two integers, normal addition is performed.
Imagine you are developing a text editor that frequently alters strings (like undo, redo, replace, cut, copy, and paste operations). Which class(es) would you utilize for efficient memory and performance management?
- String and PhantomReference
- StringBuffer and SoftReference
- StringBuilder and WeakReference
- StringJoiner and ReferenceQueue
In a text editor, where efficient memory and performance management are crucial, StringBuilder is used for in-place string manipulation, and WeakReference helps in memory management by allowing objects to be garbage collected when not strongly referenced. StringBuffer is thread-safe but may not provide the best performance. The other options are not suitable for such scenarios.