QUESTION: What is the difference between yielding and sleeping?
ANSWER: When a task invokes its yield() method, it returns to the ready state. When a task invokes its sleep() method, it returns to the waiting state.
QUESTION: When a thread blocks on I/O, what state does it enter?
ANSWER: A thread enters the waiting state when it blocks on I/O.
QUESTION: When a thread is created and started, what is its initial state?
ANSWER: A thread is in the ready state after it has been created and started.
QUESTION: What invokes a thread's run() method?
ANSWER: After a thread is started, via its start() method or that of the Thread class, the JVM invokes the thread's run() method when the thread is initially executed.
QUESTION: What method is invoked to cause an object to begin executing as a separate thread?
ANSWER: The start() method of the Thread class is invoked to cause an object to begin executing as a separate thread.
QUESTION: What is the purpose of the wait(), notify(), and notifyAll() methods?
ANSWER: The wait(),notify(), and notifyAll() methods are used to provide an efficient way for threads to wait for a shared resource. When a thread executes an object's wait() method, it enters the waiting state. It only enters the ready state after another thread invokes the object's notify() or notifyAll() methods.
QUESTION: What are the high-level thread states?
ANSWER: The high-level thread states are ready, running, waiting, and dead
QUESTION: What happens when a thread cannot acquire a lock on an object?
ANSWER: If a thread attempts to execute a synchronized method or synchronized statement and is unable to acquire an object's lock, it enters the waiting state until the lock becomes available.
QUESTION: How does multithreading take place on a computer with a single CPU?
ANSWER: The operating system's task scheduler allocates execution time to multiple tasks. By quickly switching between executing tasks, it creates the impression that tasks execute sequentially.
QUESTION: What happens when you invoke a thread's interrupt method while it is sleeping or waiting?
ANSWER: When a task's interrupt() method is executed, the task enters the ready state. The next time the task enters the running state, an InterruptedException is thrown.
QUESTION: What state is a thread in when it is executing?
ANSWER: An executing thread is in the running state
QUESTION: What are three ways in which a thread can enter the waiting state?
ANSWER: A thread can enter the waiting state by invoking its sleep() method, by blocking on I/O, by unsuccessfully attempting to acquire an object's lock, or by invoking an object's wait() method. It can also enter the waiting state by invoking its (deprecated) suspend() method.
QUESTION: What method must be implemented by all threads?
ANSWER: All tasks must implement the run() method, whether they are a subclass of Thread or implement the Runnable interface.
QUESTION: What are the two basic ways in which classes that can be run as threads may be defined?
ANSWER: A thread class may be declared as a subclass of Thread, or it may implement the Runnable interface.
