Java Core Classes and Threads

The question requires storing currencies (keys) with USD prices (values) in a thread-safe manner. HashSet and HashMap are not synchronized. Vector is synchronized but is a List, not a Map. TreeMap is not inherently synchronized. Hashtable would be the correct synchronized Map choice, but it's not listed. Therefore 'None of the above' is correct.

The question asks for a collection that maintains entries by last-accessed order. HashSet doesn't maintain any access order. Hashtable is synchronized but doesn't track access order. Vector maintains insertion order, not access order. LinkedHashMap with accessOrder=true would be correct, but plain LinkedHashMap (default) maintains insertion order, not access order. Hence none of these are correct.

In Java, IllegalArgumentException is the standard runtime exception thrown to indicate that a method has been passed an illegal or inappropriate argument. AssertionError is for internal invariants, and IllegalStateException is for invalid object states.

A thread continues running after start() completes; it executes the run() method. Thread priority is set via setPriority(), not constructor (in Java). notify() wakes waiting threads, not sleeping ones. Option D is correct because Java requires holding an object's lock before calling notify() on it.

Thread.sleep(10000) guarantees that the thread will sleep for at least 10,000 milliseconds (10 seconds) before resuming, unless interrupted. It does not guarantee an exact execution time due to OS scheduling overhead, but it ensures at least 10 seconds have elapsed.

wait() is an instance method of Object class (A), must be called in synchronized context (F), and requires the calling thread to hold the object's lock (D). It's not static (B), not in Thread class (C), and multiple threads can wait on the same object (E). Three options are correct.

In Java, synchronized methods can be overridden to be non-synchronized (and vice versa) because synchronization is a property of the implementation, not the method signature. Additionally, while a thread holds a lock on a synchronized method, other threads can freely access non-synchronized methods.

When a client attempts to connect to a server that is not running, Java throws a ConnectException. This is a runtime exception indicating the connection was refused because no server is listening at the specified host and port.

The transient modifier in Java tells the JVM to skip that field during serialization - it won't be written to the persistent stream. This is useful for fields that can be recalculated, are derived from other data, contain sensitive information, or reference non-serializable objects.

Hashtable extends the abstract Dictionary class, which was part of Java's original collection framework in version 1.0. While Dictionary is now deprecated and Hashtable implements the Map interface (since Java 2), Dictionary remains its direct superclass in the class hierarchy.

When a Java program starts, the JVM creates several threads beyond the main thread, including garbage collector threads and possibly other JVM-internal threads for monitoring, JIT compilation, and other runtime services. The main thread is just one of many threads running from the beginning.

In JUnit 3, methods must start with 'test' to be recognized, but JUnit 4+ uses annotations like @Test and allows any method name. The statement is false because method naming conventions vary by framework version.

Console.readPassword() reads password input from the console with echoing disabled (characters don't appear on screen). It returns char[] not String for security (can be cleared from memory).