An important trend in programming languages is support for data encapsulation, or object-oriented code. Data encapsulation is best illustrated by the language Smalltalk, in which all programming is done in terms of so-called objects. An object in Smalltalk or similar object-oriented languages consists of data together with the procedures (program segments) to operate on that data. Encapsulation refers to the fact that an object’s data can be accessed only through the methods (procedures) provided. Programming is done by creating objects that send messages to one another so that tasks can be accomplished cooperatively by invoking each others’ methods. This object-oriented paradigm has been very influential. For example, the language C, which was popular for engineering applications and systems development, has largely been supplanted by its object-oriented extension C++. An object-oriented version of BASIC, named Visual BASIC, is available for personal computers and allows even novice programmers to create interactive applications with elegant graphical user interfaces (GUIs).
In 1995 Sun Microsystems, Inc., introduced Java, yet another object-oriented language. Applications written in Java are not translated into a particular machine language but into an intermediate language called Java Bytecode, which may be executed on any computer (such as those using UNIX, Macintosh, or Windows operating systems) with a Java interpretation program known as a Java virtual machine. (See Program translation below.) Thus Java is ideal for creating distributed applications or Web-based applications. The applications can reside on a server in Bytecode form, which is readily downloaded to and executed on any Java virtual machine. In many cases it is not desirable to download an entire application but only an interface through which a client may communicate interactively with the application. Java applets (small chunks of application
code) solve this problem. Residing on Web-based servers, they may be downloaded to and run in any standard Web browser to provide, for example, a client interface to a game or database residing on a server.
Concurrency refers to the execution of more than one procedure at the same time (perhaps with the access of shared data), either truly simultaneously (as on a multiprocessor) or in an unpredictably interleaved manner. Languages such as Ada (the U. S. Department of Defense standard applications language from 1983 until 1997) include both encapsulation and features to allow the programmer to specify the rules for interactions between concurrent procedures or tasks.
At a still higher level of abstraction lie visual programming languages, in which programmers graphically express what they want done by means of icons to represent data objects or processes and arrows to represent data flow or sequencing of operations. As of yet, none of these visual programming languages has found wide commercial acceptance. On the other hand, high-level user-interface languages for special-purpose software have been much more successful; for example, languages like Mathematica, in which sophisticated mathematics may be easily expressed, or the “fourth generation” database-querying languages that allow users to express requests for data with simple English-like commands. For example, a query such as “Select salary from payroll where employee = ‘Jones,’ ” written in the database language SQL (Structured Query Language), is easily understood by the reader.