Java Programing

either declare the exceptions it can generate or catch and deal with them itself. This promotes error information to the same level of importance as argument and return typing. As a Java programmer, you know precisely what exceptional conditions you must deal with, and you have help from the compiler in writing correct software that doesn’t leave them unhandled. 1.4.6 Multithreading 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. For complete coverage of threads, refer to Java Threads, by Scott Oaks and Henry Wong (O’Reilly & Associates). 1.4.7 Scalability At the lowest level, Java programs consist of classes. Classes are intended to be small, modular components. They can be separated physically on different systems, retrieved dynamically, stored in a compressed format, and even cached in various distribution schemes. Over classes, Java provides packages , a layer of structure that groups classes into functional units. Packages provide a naming convention for organizing classes and a second level of organizational control over the visibility of variables and methods in Java applications. Within a package, a class is either publicly visible or protected from outside access. Packages form another type of scope that is closer to the application level. This lends itself to building reusable components that work together in a system. Packages also help in designing a scalable application that can grow without becoming a bird’s nest of tightly coupled code dependency. 1.5 Safety of Implementation It’s one thing to create a language that prevents you from shooting yourself in the foot; it’s quite another to create one that prevents others from shooting you in the foot. Encapsulation is a technique for hiding data and behavior within a class; it’s an important part of object-oriented design. It helps you write clean, modular software. In most languages, however, the visibility of data items is simply part of the relationship between the programmer and the compiler. It’s a matter of semantics, not an assertion about the actual security of the data in the context of the running program’s environment. When Bjarne Stroustrup chose the keyword private to designate hidden members of classes in C++, he was probably thinking about shielding you from the messy details of a class developer’s - 14

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