Creating a Java Program

1
Creating a Java Program

• by mr. Hanley
• 2/2/2007

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How do we create a java program?

• Steps
• Create a .java file with an editor
• Notepad, Jbuilder, BlueJ, JCreator, Eclipse
• AlgoPractice1.java saved
• Compile the program using javac
• javac AlgoPractice1.java
• AlgoPractice1.class is created if successful
• Execute the program by launching VM
• javaw AlgoPractice1.class

3
How does the VM work?

• The Java Virtual Machine is responsible for
  loading in your program and interpreting it on
  your current platform(Operating System)
• Thus, java is compiled at build time and
  interpreted at run time

4
How does java live up to Suns write once, run
everywhere motto?
library and user .class
AlgoPract1.class
Sun JVM
Windows JVM
Mac JVM
Solaris (Unix)
Windows XP
Mac OS
Sun Server Hardware
PC Hardware
Mac Hardware
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JVM interprets commands

• The JVM must take the .class files that you
  create via the compiler and translate them into
  commands for the particular operating system you
  are running on

6
Jbuilders approach

• New class allows you to edit a .java file (src
  directory)
• Note Comments dont compile
• Make attempts to compile your .java file and
  creates a .class file (classes directory)
• Run Project attempts to load .class file
  specified in project settings
• must have a main method in order to execute

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Run project

• Choosing Run Project(F9) or the Play Button will
  attempt to do both of the 2nd and 3rd prior steps
• It will compile any files that are changed
• It will attempt to start up the JVM