When a class implements Serializable, it should have a static final field named ______.
- classVersion
- serialVersion
- serialVersionUID
- versionID
When a class implements the Serializable interface, it's recommended to have a static final long serialVersionUID field. This field helps ensure that the serialized and deserialized versions of the class are compatible. It's used to verify that the class being deserialized is compatible with the one that was originally serialized. The other options are not standard.
How can you configure the thread names of an ExecutorService for debugging and identification purposes?
- Thread names are automatically derived from the name of the task submitted to the ExecutorService.
- You can change thread names by calling the setName method on the ExecutorService instance after it's created.
- You can set the thread names when creating a new thread pool using the ThreadFactory interface and providing a custom ThreadFactory implementation.
- You cannot configure thread names for threads in an ExecutorService; they are automatically generated by Java.
To configure thread names of an ExecutorService for debugging and identification purposes, you can provide a custom ThreadFactory implementation when creating the thread pool. This allows you to set meaningful names for the threads, making it easier to identify their purpose in logs and debugging. Thread names are not automatically configurable and are typically based on the default naming conventions unless you specify otherwise.
The class ________ allows an application to write primitive Java data types to an output stream in a portable way.
- ByteArrayOutputStream
- DataOutputStream
- ObjectOutputStream
- PrintStream
The class ObjectOutputStream in Java is used for writing primitive Java data types to an output stream in a portable way. It provides methods for writing various data types to the stream.
If multiple case labels match the switch expression, then only the ________ matching case will be executed.
- all
- first
- first-matching
- last
When there are multiple case labels that match the switch expression in Java, only the first-matching case will be executed. Subsequent cases with matching labels will be ignored, ensuring that only the first matching case block is executed.
Considering threading, which collection class might introduce higher overhead in managing read and write access?
- ArrayList
- HashSet
- CopyOnWriteArrayList
- ConcurrentHashMap
In Java, when considering threading and concurrent access, the CopyOnWriteArrayList can introduce higher overhead in managing read and write access. This is because it creates a new copy of the underlying array every time a modification operation is performed (e.g., add or remove). While this ensures thread safety during iterations, it can be inefficient for scenarios with frequent write operations. So, option (c) is correct, with the explanation that CopyOnWriteArrayList is used for thread-safe iteration but may introduce overhead in write operations.
To retrieve the result of a computation from a Future, you use the ________ method.
- acquire()
- fetch()
- get()
- obtain()
In Java, to retrieve the result of a computation from a Future object, you use the get() method. The get() method blocks until the computation is complete and then returns the result. This is a fundamental method when working with concurrent programming and asynchronous tasks.
The method read() of FileReader class returns ________ when the end of the file is reached.
- True
- -1
- 0
- FALSE
The read() method of the FileReader class returns -1 when the end of the file is reached. This indicates that there are no more characters to read from the file.
The ________ interface provides methods to retrieve the meta data of the database such as its structure (tables, schemas), the user on the connection, etc.
- ConnectionMetaData
- DatabaseMetaData
- ResultSetMetaData
- StatementMetaData
The DatabaseMetaData interface in JDBC provides methods for retrieving metadata about the database, including information about its structure (tables, schemas), the user associated with the connection, and more. It's essential for database introspection and querying the database schema. The other options are not used for this purpose.
How does Java handle overriding methods that throw exceptions?
- The overridden method must declare exceptions
- The overriding method cannot declare exceptions
- The overriding method may declare exceptions
- The overriding method must declare exceptions
In Java, when a subclass overrides a method from its superclass, it must adhere to the method signature, including the exceptions it can throw. If the superclass method declares exceptions, the overriding method can declare the same exceptions or subtypes of those exceptions. This rule ensures that the subclass does not throw unexpected exceptions.
What will be the output of the following code snippet: System.out.println("2" + 3);?
- "23"
- "5"
- 23
- Compilation error
In this code snippet, Java performs string concatenation when you use the '+' operator with a string and another data type. So, "2" + 3 results in "23". The integer 3 is automatically converted to a string and then concatenated with "2".