Multithreading of Java

Applications today require a high degree of parallelism. Even a very single- minded application can have a complex user interface—which requires concurrent activities. As machines get faster, users become more sensitive to waiting for unrelated tasks that seize control of their time. Threads provide efficient multiprocessing and distribution of tasks for both client and server applications. Java makes threads easy to use because support for them is built into the language. Concurrency is nice, but there’s more to programming with threads than just performing multiple tasks simultaneously. In many cases, threads need to be synchronized, which can be tricky without explicit language support. Java supports synchronization based on the monitor and condition model developed by C.A.R. Hoare—a sort of lock and key system for accessing resources. The keyword
synchronized designates methods for safe, serialized access within an object. Only one synchronized method within the object may run at a given time. There are also simple, primitive methods for explicit waiting and signaling between threads interested in the same object. Learning to program with threads is an important part of learning to program in Java. See Chapter 8, for a discussion of this topic.