51. What is the purpose of the assert statement in Java?
The assert statement is used to test assumptions in code. If an assertion fails, it throws an AssertionError, aiding in identifying bugs during development. Assertions are typically disabled at runtime and should not replace standard error handling. GeeksforGeeks
Q52. How do ArrayList and LinkedList differ in Java?
- ArrayList: Uses a dynamic array, offering fast random access (O(1)), but slower insertions/deletions (O(n)).
- LinkedList: Implemented as a doubly-linked list, providing efficient insertions/deletions (O(1)), but slower random access (O(n)).
Q53. What is the role of the hashCode() method in Java?
The hashCode() method returns an integer hash code for an object, which is used in hash-based collections like HashMap, HashSet, and Hashtable to determine the bucket location for storing objects.
Q54. Why is the toString() method important in Java?
The toString() method provides a string representation of an object, useful for debugging and logging. Overriding this method allows developers to display object information in a readable format.
Q55. How is encapsulation achieved in Java?
Encapsulation is implemented by declaring class variables as private and providing public getter and setter methods to access and modify them. This restricts direct access to class internals and promotes data integrity.
Q56. What are method references in Java?
Method references are a shorthand notation of lambda expressions to call methods directly. They enhance code readability and are represented using the :: operator. For example: String::toUpperCase. GeeksforGeeks
Q57. What are annotations in Java?
Annotations are metadata that provide information about the program but are not part of the program itself. They can influence program behavior at compile-time or runtime and are denoted by the @ symbol, such as @Override or @Deprecated. Oracle Docs
Q58. What is the BitSet class used for in Java?
The BitSet class represents a set of bits or flags that can be set, cleared, and flipped individually. It’s efficient for handling large sets of boolean values and supports logical operations like AND, OR, and XOR. Oracle Docs
Q59. What is a CyclicBarrier in Java?
A CyclicBarrier is a synchronization aid that allows a set of threads to all wait for each other to reach a common barrier point. It’s useful in scenarios where threads must wait for others to complete before proceeding.
Q60. What are the types of JDBC statements in Java?
- Statement: Used for executing static SQL queries without parameters.
- PreparedStatement: Precompiled SQL statement with parameters, enhancing performance and security.
- CallableStatement: Used to execute stored procedures in the database.
Q61. What is the Java String Pool?
The Java String Pool is a special memory region where string literals are stored to optimize memory usage. When a new string literal is created, the JVM checks the pool first; if the string exists, it returns the reference, avoiding duplicate objects. Baeldung+1CodeHS+1
Q62. What is the difference between Path and Classpath?
- Path: An environment variable used by the operating system to locate executable files.
- Classpath: Used by the JVM to locate user-defined classes and packages. Stack Overflow
Q63. How do Heap and Stack memory differ in Java?
- Heap Memory: Used for dynamic memory allocation for Java objects and JRE classes.
- Stack Memory: Stores method calls and local variables. Each thread has its own stack. Oracle Docs+8GeeksforGeeks+8Oracle Docs+8DigitalOcean+1Baeldung+1
Q64. Can we use String with a switch-case statement?
Yes, from Java 7 onwards, strings can be used in switch-case statements. The switch statement compares the string’s hash code and then checks for equality. Oracle Docs
Q65. What are the different types of class loaders in Java?
- Bootstrap ClassLoader: Loads core Java classes.
- Extension ClassLoader: Loads classes from the JDK’s extensions directory.
- System ClassLoader: Loads classes from the application’s classpath.
Q66. What is the difference between fail-fast and fail-safe iterators?
- Fail-Fast Iterators: Immediately throw ConcurrentModificationException if the collection is modified during iteration.
- Fail-Safe Iterators: Operate on a cloned copy of the collection, allowing modifications without exceptions.
Q67. What is a compile-time constant in Java?
A compile-time constant is a variable declared as static final and initialized with a constant expression. Its value is determined at compile time and cannot be changed.
Q68. What is the difference between Map and Queue in Java?
- Map: An object that maps keys to values, with no duplicate keys.
- Queue: A collection designed for holding elements prior to processing, typically in FIFO (first-in-first-out) order.
Q69. What is the difference between LinkedHashMap and PriorityQueue?
- LinkedHashMap: Maintains insertion order of keys.
- PriorityQueue: Orders elements based on their natural ordering or a provided comparator.
Q70. What is a memory-mapped buffer in Java?
A memory-mapped buffer allows a file to be mapped into memory, enabling faster file I/O operations by reading and writing directly to memory. It’s useful for large files and can improve performance significantly.
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