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Java and JavaScript

Comparative characteristics of JavaScript and Java.

Basically, Java and JavaScript differ in the number of features and complexity. JavaScript has a freer implementation than Java, so for example, you can choose not to declare variables, and it is easier to convert data types. In addition, the source code of a program in JavaScript does not need to be compiled, unlike Java applets: the JavaScript language is interpreted. The JavaScript interpreter reads the program line by line and reports errors (if any) after each line it reads (and not after processing the entire text of the program, as the Java compiler does). The source code of a Java program must be converted to a byte-byte-byte format before the program is executed, and therefore JavaScript programs can be developed and debugged much faster.

Like the Java language, JavaScript is an object-oriented language, although it has neither the classes nor the built-in inheritance mechanisms that are standard for Java. Java programs use object classes, and these programs are completely object-oriented. Both Java and JavaScript are among the safe languages - in the sense that each of them supports tools that do not allow data received from an unknown source to be written to the hard disk. As for the portability of code written in these two languages, there are slight differences. A compiled Java program will be executed by any "Java-oriented" browser. JavaScript initially only required a 32-bit version of Netscape 2.0, but it can now run on a 16-bit platform.

What can I use JavaScript for?

All events that are generated by the Netscape Navigator browser, such as button clicks, field processing, and movement between pages, can be intercepted and processed by JavaScript. This capability is very important because you can use it to create applications with a specific structure.

The JavaScript language provides, in addition to the means of processing individual user requests for hyperlinks, the ability to recognize the moment of transition to another page and perform appropriate actions when this event occurs. The JavaScript language is perfect for solving routine daily tasks, such as data validation, form processing, as well as for performing actions on string and numeric values, i.e. those tasks that cannot be solved using existing dialects of the HTML language. With it, you can dynamically create HTML documents, that is, such documents that are created by a program in the JavaScript language, and the user himself. Therefore, the document can manage the structure of the document according to the specified rules. Most importantly, with the advent of JavaScript, the static nature of HTML pages became a thing of the past. The following are the main areas of application of the JavaScript language:

  • Dynamically create an HTML document using a program
  • Validating HTML Form Fields Before Uploading Them to the Server
  • Locally enter information to control a JavaScript program
  • Allow the user to choose which operations the browser performs
  • Display messages to the user (such as warnings) in the appropriate windows
  • Local form processing, local user input, and other "home" tasks

Learning JavaScript will help novice programmers prepare to learn the more complex and important Java language. Both JavaScript and Java are full-fledged programming languages; they use similar means. We can even say that the JavaScript language is a kind of model of the Java language. A Java program also uses classes and their methods, but it is more complex than JavaScript because java must declare classes and implement their methods.

It is important to clearly delineate the applicability of each of these programming environments. JavaScript has never been considered a replacement for Java; ideally, it should be used as a supplement to the Java language, allowing you to merge the entire operating environment of a Web application together and provide it to the user. Java is used primarily to solve "critical tasks", for example, to develop graphical user interfaces, whereas the JavaScript language is designed to tie together all the building blocks of an application. In short, JavaScript is essentially a foundation-building tool.

The requirements of the JavaScript language are also significantly less stringent in matters of syntax and type checking. The Java compiled system is based on the concept of classes that are implemented by declaring them. JavaScript is implemented as an interpreter (that is, no object code is generated) with a small number of primitive base types, which include strings, as well as numeric and Boolean types. You can also build objects based on primitive types by defining their properties using the assignment operator. The main thing to always remember when developing scripts is that Web pages are quickly becoming a thing of the past; the emphasis is now on completed "applications" that are combined into a single whole using technologies such as Java, JavaScript and HTML.


Originally, JavaScript was to be called LiveScript and more like Scheme, one of the dialects of Lisp. But at that time, Java was just out, so Netscape marketers renamed the language and made the syntax Java-like, for better promotion in the market. Now even in the syntax there are differences (for example, arrows for anonymous functions: -> in Java and => in ECMAScript 6).

In addition:
1) Brandon Ike was helped to develop the language by Bill Joy, one of the founders of Sun (the one where Java was invented);
2) Java (with JDK 6) includes a JavaScript interpreter that can be used in any Java application;
3) often Java and JavaScript are used instead - on the server and client, respectively;
4) there is a GUI framework GWT, which converts code written in Java into JavaScript, HTML and CSS.

Now the scripting language is officially called ECMAScript (in standards, for example), but the old name is also used for compatibility.