Deadlock is an unrecoverable state sometimes encountered in thread programming. It occurs under the following circumstances: thread A has a lock on object X, and is waiting for the lock to object Y; meanwhile, thread B has the lock on object Y, and is waiting for the lock on object X. In the event of a deadlock, program execution will simply suspend indefinitely, making it difficult to debug.
A statement that creates an identifier and associates attributes with it. Declaring a data item may or may not reserve memory space. A method declaration may or may not also provide the implementation.
A Java keyword used within a switch block to indicate the code block to execute if no case value matches the switch value.