Java Compiler
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Java Language
The
Java language has its own structure, syntax rules, and programming paradigm
like any programming language. The Java language's programming paradigm is
based on the concept of OOP, which the language's features support.
Java Compilation
When
you write program for the Java platform, you write source code in .java files
and then compile them. The compiler checks your code against the language's
syntax rules, then writes out byte code in .class files. Byte code is
a set of instructions targeted to run on a Java virtual machine (JVM). In
adding this level of abstraction, the Java compiler differs from other language
compilers, which write out instructions suitable for the CPU chipset the
program will run on.
Public
class MyFirstJavaProgram {
/* this is my first java program.
* This will print 'Hello World' as the
output
*/
Public
static void main (String [] args) {
System.out.println
("Hello World"); // prints Hello World
}
}
Let's Folow
these steps how to save the file, compile and run the program.
·
Open notepad and add the code
as above.
·
Save the file as:
MyFirstJavaProgram.java.
·
Open a command prompt window
and go to the directory where you saved the class. Assume its C:\.
·
Type ' javac
MyFirstJavaProgram.java' and press enter to compile your code. If there are no
errors in your code, the command prompt will take you to the next line (Assumption:
The path variable is set).
·
Now, type ' java
MyFirstJavaProgram ' to run your program.
You
will be able to see ' Hello World ' printed on the window.
C :\>javac MyFirstJavaProgram.java
C :\> java MyFirstJavaProgram
Basic Syntax:
About
Java programs, it is very important to keep in mind the following points:
Case
Sensitivity - Java is case sensitive, which means
identifier Helloand hello would have different meaning in Java.
Class
Names - For all class names the first letter should be in Upper
Case.
If several words are used to form a name of the class, each inner word's first letter should be in Upper Case.
If several words are used to form a name of the class, each inner word's first letter should be in Upper Case.
Example class
MyFirstJavaClass
Method
Names - All method names should start with a Lower Case letter.
If several words are used to form the name of the method, then each inner word's first letter should be in Upper Case.
If several words are used to form the name of the method, then each inner word's first letter should be in Upper Case.
Example public
void myMethodName ()
Program
File Name - Name of the program file should exactly match the class
name.
When saving the file, you should save it using the class name (Remember Java is case sensitive) and append '.java' to the end of the name (if the file name and the class name do not match your program will not compile).
When saving the file, you should save it using the class name (Remember Java is case sensitive) and append '.java' to the end of the name (if the file name and the class name do not match your program will not compile).
Example:
Assume 'MyFirstJavaProgram' is the class name. Then the file should be saved
as 'MyFirstJavaProgram.java'
Public
static void main(String args[]) - Java program processing starts from the
main() method which is a mandatory part of every Java program.
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