Which of the following is an invalid variable name in Java?
- $myVar
- 123var
- _myVariable
- myVar1
In Java, variable names must start with a letter, underscore (_), or dollar sign ($) and may be followed by letters, digits, underscores, or dollar signs. Option 2 (123var) is invalid because it starts with a digit, which is not allowed.
The ________ keyword is used to declare objects that cannot change.
- final
- static
- transient
- volatile
The final keyword in Java is used to declare objects that cannot change after they are initialized. It can be applied to variables, methods, and classes to make them unmodifiable, constant, or not extendable, respectively.
The method replace(oldChar, newChar) belongs to the ________ class in Java.
- Character
- String
- StringBuilder
- StringManipulator
The replace(oldChar, newChar) method in Java belongs to the String class. This method is used to replace all occurrences of oldChar with newChar in a given string. The other classes listed do not have this specific method.
The process of converting a primitive data type to a wrapper class object in Java is known as ________.
- Autoboxing
- Casting
- Parsing
- Unboxing
The process of converting a primitive data type to a wrapper class object in Java is known as "Autoboxing." Autoboxing is the automatic conversion of primitive data types to their corresponding wrapper classes. For example, converting an int to an Integer.
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.
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.