>723643 Grundbegriffe der Java -Programmierung

Fundamental Concepts of Java  Programming

Texts

A text  is a sequence of characters  or of lines  (each of which is a sequence of characters ).

Example of a text with four lines

,yX@AI2["x/z-P%H%){5j{U)WW.8!4,V}x"!?90lkPycj-|Jy.aj5)O)
JO&!rgN:3^Y"K@?wb1Y!_\\&xQ|]@QR-n9[Lgz+bo*8, wLxX*vC4j3(h
eSZ2j[RR|SFYwg7A1x=}9r g\as}Q@BV
xIckHxFec>

A text editor  is a program for writing and modifying text.

A file that has been saved under a name is called a text file  (or plain text file ).

A text editor also enables us to save texts as text files or to read texts from text files.

When a program is being started, sometimes files are created automatically, which will be processed again later. Source text  is a text that is not  generated automatically from another text, but rather is a source for subsequent steps of processing.

Source text also is know as source code  and usually is written by humans. When source test has been saved into a file, that file also is called a source file.

Programs

A programming language  establishes that certain texts are programs. The rules to determine this are called the syntax  of the programming language.

A programming language  also establishes what the programs mean. The rules to determine this are called the semantics  of the programming language.

Since every program also is a text, text editors can be used to edit programs and to save them as text files.

A program can be used to specify up front what a computer is supposed to do later. This usually allows one to program everything the computer can do as a device. For example, when a computer has a loudspeaker, one can write a program that uses this loudspeaker to emit sounds.

Java 

Java  is a programming language.

A Java  program is a text that is a program according to the syntax of Java.

Example of a Java  program with four lines

public final class Main
{ public static void main( final java.lang.String[] args )
  { java.lang.System.out.println
    ( "hello, world!" ); }}

Implementations

To execute  a program means to do what the program requires according to the semantics of its programming language.

A Java  implementation is a machine that is able to execute Java  programs. The word “implementation” means as much as as “conversion”, “actualization”, or “realization”. Provided that there is no risk of confusion with other types of implementations, a Java  implementation can simply be called an “implementation ”.

The execution of a program by an implementation

 .-------.     .----------------.
( program )--->| implementation |
 '-------'     '----------------'
                       |
                       V
                    \      /
                   - action -
                    /      \

Programming  is the activity of writing of programs, that is, controlling an implementation with pre-written text files. Given that programs today control just about everything from elevators to TV sets, we can say that our world is controlled by text files!

A good programmer can, for example, write down (in English!) how the laces of shoes are tied, so that somebody who does not know how to tie laces can learn this from the text in an unambiguous way and without the need to ask the author any questions about the test.

A text that is to be executed as a Java program will first be checked for errors using a program that is called a compiler  or translator. So when a program is being compiled, it is being check for errors by the compiler.

The compiler also prepares a program for execution, so one can say that an implementation often consists of a compiler and an executor.

implementation = compiler + executor

Development Systems

To develop  a program means to write  the program.

A Java  development system (also known as a Java  development environment ) is a system that can be used to develop Java  programs. Usually, it contains a text editor and a Java implementation. The text editor is being used to write and save  programs, while the Java  implementation is used to start  programs.

development system = editor + implementation