Writing and Executing a Java Program - Revizia istoricului

Rhobincu: /* Program Execution Inside the Virtual Machine */

2013-10-22T09:44:50Z

Program Execution Inside the Virtual Machine

Rhobincu la 22 octombrie 2013 09:44

2013-10-22T09:44:35Z

Rhobincu: /* Compiling the Source */

2013-10-22T09:15:14Z

Compiling the Source

Rhobincu: Pagină nouă: In order to develop a Java program, there are two operations that need to be performed: the compilation of a source code and the execution of the program inside the virtual machine. T...

2013-10-22T08:59:30Z

Pagină nouă: In order to develop a Java program, there are two operations that need to be performed: the compilation of a source code and the execution of the program inside the virtual machine. T...

Pagină nouă

In order to develop a Java program, there are two operations that need to be performed: the compilation of a source code and the execution of the program inside the virtual machine. The source code can be written in any text editor. For Microsoft Windows, a good suggestion is [http://notepad-plus-plus.org/ Notepad++]. For Linux, depending on the X interface, you can use either ''Kate'' for KDE or ''gedit'' for Gnome/ Unity/ Cinnamon. During this lab, we will be using ''Kate''. You can run it by clicking Applications -> Accessories -> Kate.

== Command Line Tutorial ==

Before compiling and executing a Java program, we will need a short introduction for using the console in both MS Windows and Linux.

=== MS Windows cmd ===

In Windows, the console is stated by pressing "winkey + r", then typing ''cmd''. It looks like this:

[[Fișier:cmd.png|Consola sistemului de operare Windows]]

A few useful commands:

* if the files are on another partition, like D, or E, the command that changes the path to the D partition, for example, is:
<syntaxhighlight lang="dos">
c:\Users\Echo> d:
d:\>
</syntaxhighlight>
* for changing the current directory, the ''cd'' command is used (change directory):
<syntaxhighlight lang="dos">
c:\Users\Echo> cd Documents
c:\Users\Echo\Documents> cd work
c:\Users\Echo\Documents\work> cd ..
c:\Users\Echo\Documents>
</syntaxhighlight>
* for displaying the content of the current directory, you can use the ''dir'' command:
<syntaxhighlight lang="dos">
C:\Users\Echo\Documents\work\poo> dir
Volume in drive C has no label.
Volume Serial Number is 9C96-4AC6

Directory of C:\Users\Echo\Documents\work\poo

18-Jul-12 10:42 <DIR> .
18-Jul-12 10:42 <DIR> ..
18-Jul-12 10:43 117 MainClass.java
1 File(s) 117 bytes
2 Dir(s) 22,145,564,672 bytes free

C:\Users\Echo\Documents\work\poo>
</syntaxhighlight>
* for creating a new directory, use ''md'' (make directory):
<syntaxhighlight lang="dos">
C:\Users\Echo\Documents\work\poo> md test

C:\Users\Echo\Documents\work\poo> dir
Volume in drive C has no label.
Volume Serial Number is 9C96-4AC6

Directory of C:\Users\Echo\Documents\work\poo

18-Jul-12 10:45 <DIR> .
18-Jul-12 10:45 <DIR> ..
18-Jul-12 10:43 117 MainClass.java
18-Jul-12 10:45 <DIR> test
1 File(s) 117 bytes
3 Dir(s) 22,145,433,600 bytes free

C:\Users\Echo\Documents\work\poo>
</syntaxhighlight>

=== Linux Bash ===

In Linux, depending on the distribution and interface, you can start the terminal by either pressing "Alt + Ctrl + T", or by selecting '''Terminal''' from Applications -> Accessories:

[[Fișier:linux_console.png|Consola din Linux]]

A few useful commands:
* to display the current directory, use ''pwd'' (print working directory):
<syntaxhighlight lang="bash">
student@olympus07:~$ pwd
/home/student
student@olympus07:~$
</syntaxhighlight>
* for changing the current directory, the ''cd'' command is used (change directory):
<syntaxhighlight lang="bash">
student@olympus07:~$ cd work
student@olympus07:~/work$ pwd
/home/student/work
student@olympus07:~/work$ cd ..
student@olympus07:~$ pwd
/home/student
student@olympus07:~$
</syntaxhighlight>
* for displaying the content of the current directory, you can use the ''ls -l'' command (list structure, long listing format):
<syntaxhighlight lang="bash">
student@olympus07:~/work/poo$ ls -l
total 4
-rw-rw-r-- 1 student student 110 Jul 18 11:08 MainClass.java
student@olympus07:~/work/poo$
</syntaxhighlight>
* to create a new directory, use ''mkdir'' (make directory):
<syntaxhighlight lang="bash">
student@olympus07:~/work/poo$ mkdir test
student@olympus07:~/work/poo$ ls -l
total 8
-rw-rw-r-- 1 student student 110 Jul 18 11:08 MainClass.java
drwxrwxr-x 2 student student 4096 Jul 18 11:10 test
student@olympus07:~/work/poo$
</syntaxhighlight>

== Writing, Compiling and Executing a Java Program ==

=== Editing the Source Code ===

The first step in writing a Java program, is editing the source code. For this, use your favorite editor and save the file with a .java extension.

<div class="regula"><font color="#ff0000">Rule:</font> A Java source code will '''always''' have a .java extension.</div>

<div class="regula"><font color="#ff0000">Rule:</font> The name of a class contained in a source file must '''always''' have the same identical name with the file. I.e.: The class MainClass '''must''' be saved in a file named MainClass.java. '''Attention''': Java is case-sensitive!!!</div>

For example, we will write the following class:
<syntaxhighlight lang="java">
public class MainClass{

public static void main(String[] _args){
System.out.println("Hello world!");
}

}
</syntaxhighlight>

This class must be saved in a file called MainClass.java.

=== Compiling the Source ===

În consolă, se navighează folosind comenzile prezentate mai sus până în directorul în care a fost salvat fișierul sursă. Apoi, folosind executabilul ''javac'' (Java Compiler), se compilează:
<syntaxhighlight lang="bash">
student@olympus07:~/work/poo$ javac MainClass.java
student@olympus07:~/work/poo$ ls -l
total 8
-rw-rw-r-- 1 student student 424 Jul 18 11:22 MainClass.class
-rw-rw-r-- 1 student student 110 Jul 18 11:08 MainClass.java
</syntaxhighlight>

<div class="regula"><font color="#ff0000">Regulă:</font> Întotdeauna, compilatorul Java va lua ca argument '''numele fișierului''' (cu tot cu extensie) care trebuie compilat.</div>

Dacă execuția compilatorului nu a afișat nici o eroare, atunci compilarea s-a încheiat cu succes și a fost generat fișierul executabil pentru mașina virtuală, cu extensia .class.

Dacă compilatorul nu a putut fi găsit, atunci verificați variabila de sistem PATH, conform instrucțiunilor de instalare pentru JDK.

Dacă compilatorul a afișat erori, citiți-le cu atenție și reparați problemele din codul sursă Java.

=== Execuția programului în mașina virtuală ===

În locul unde s-a compilat codul sursă, folosind executabilul ''java'' (mașina virtuală), se execută programul:

<syntaxhighlight lang="bash">
student@olympus07:~/work/poo$ java MainClass
Hello world!
student@olympus07:~/work/poo$
</syntaxhighlight>

<div class="regula"><font color="#ff0000">Regulă:</font> Întotdeauna, mașina virtuală Java va lua ca argument '''numele clasei''' (fără extensie) care trebuie executat.</div>

<div class="regula"><font color="#ff0000">Regulă:</font> O clasă Java nu poate fi rulată în mașina virtuală decât dacă conține metoda main, exact cum este defintă în specificație: ''public static void main(String[])''</div>

← Versiunea anterioară		Versiunea de la data 22 octombrie 2013 09:44
Linia 156:		Linia 156:


−	<div class="regula"><font color="#ff0000">Rule:</font> The JVM will '''always''' take as an argument the '''name of the class''' (without the extension) which needs to be executed.div>	+	<div class="regula"><font color="#ff0000">Rule:</font> The JVM will '''always''' take as an argument the '''name of the class''' (without the extension) which needs to be executed.</div>


	<div class="regula"><font color="#ff0000">Rule:</font> A Java class can only be ran in the virtual machine if it contains, as a member, the '''main''' method, exactly how it is defined in the specification: ''public static void main(String[])''</div>		<div class="regula"><font color="#ff0000">Rule:</font> A Java class can only be ran in the virtual machine if it contains, as a member, the '''main''' method, exactly how it is defined in the specification: ''public static void main(String[])''</div>

@@ Linia 145: / Linia 145: @@
 If the compiler displayed error messages, then read them carefully and fix the Java source code problems.
-=== Execuția programului în mașina virtuală ===
+=== Program Execution Inside the Virtual Machine ===
-În locul unde s-a compilat codul sursă, folosind executabilul ''java'' (mașina virtuală), se execută programul:
+In the directory where the source code has been compiled, using the ''java'' executable (the virtual machine), the program is executed:
 <syntaxhighlight lang="bash">
@@ Linia 156: / Linia 156: @@
-<div class="regula"><font color="#ff0000">Regulă:</font> Întotdeauna, mașina virtuală Java va lua ca argument '''numele clasei''' (fără extensie) care trebuie executat.</div>
+<div class="regula"><font color="#ff0000">Rule:</font> The JVM will '''always''' take as an argument the '''name of the class''' (without the extension) which needs to be executed.div>
-<div class="regula"><font color="#ff0000">Regulă:</font> O clasă Java nu poate fi rulată în mașina virtuală decât dacă conține metoda main, exact cum este defintă în specificație: ''public static void main(String[])''</div>
+<div class="regula"><font color="#ff0000">Rule:</font> A Java class can only be ran in the virtual machine if it contains, as a member, the '''main''' method, exactly how it is defined in the specification: ''public static void main(String[])''</div>

@@ Linia 127: / Linia 127: @@
 === Compiling the Source ===
+Open a console, navigate to the directory where the source file has been saved. Then, use the ''javac'' executable (Java Compiler) to compile the code:
 <syntaxhighlight lang="bash">
 student@olympus07:~/work/poo$ javac MainClass.java
@@ Linia 138: / Linia 137: @@
-<div class="regula"><font color="#ff0000">Regulă:</font> Întotdeauna, compilatorul Java va lua ca argument '''numele fișierului''' (cu tot cu extensie) care trebuie compilat.</div>
+<div class="regula"><font color="#ff0000">Rule:</font> The Java compiler will '''always''' take as argument the '''file name''' (extension included) which needs to be compiled. </div>
-Dacă execuția compilatorului nu a afișat nici o eroare, atunci compilarea s-a încheiat cu succes și a fost generat fișierul executabil pentru mașina virtuală, cu extensia .class.
+If the compilation did not display any message, then it has completed successfully and the executable file for the virtual machine has been created (.class extension).
-Dacă compilatorul nu a putut fi găsit, atunci verificați variabila de sistem PATH, conform instrucțiunilor de instalare pentru JDK.
+If the compiler could not be found, then check the PATH environment variable as per the JDK installation instructions.
-Dacă compilatorul a afișat erori, citiți-le cu atenție și reparați problemele din codul sursă Java.
+If the compiler displayed error messages, then read them carefully and fix the Java source code problems.
 === Execuția programului în mașina virtuală ===