Java Tips (memo)

• Assumption
• jar file: how to make/execute it.
• javadoc: how to make it.
• How to make a beep sound
• How to make a program which can run in both as an applet and as an application.
• Can I handle an URL name or a file name transparently?

Assumption

      topdir/package/name/prog.java

jar file

• How to make a executable jar file. (path and filename are assumed as the assumption.)

        jar cmf mainClass prog.jar topdir/
       

  Here, the character order of the option ``cmf'' is not changeable. `m' and `f' tells order of argments. Then, it means cmf: create, m = mainClass, f = prog.jar. The contain of the file mainClass is:

        Main-Class: topdir/package/name/prog
       

  NOTICE: This file seems needing a newline of this line. In such case, you find next message: ``Failed to load Main-Class manifest attribute from prog.jar''

• How to execute a jar file. (path and filename are assumed as the assumption.)

        java -jar prog.jar 
        

javadoc

• How to make javadoc files. (path and filename are assumed as the assumption.)

       javadoc -verbose -version -author topdir/package/name
       (javadoc -verbose -encoding EUCJIS -version -author topdir/package/name
        ... in case you want to use Japanese with encoding EUCJIS)
       

Programming

How to make a beep sound in Java.

      java.awt.Toolkit.getDefaultToolkit().beep();

How to make a program which can run in both as an applet and as an application.

There is a good utility class which is called com.sun.j3d.utils.applet.MainFrame in java3d. You can just new an applet and put it to the MainFrame for making an application. This code also works as an applet. Next is a sample code.

• LabelTest.java source code
• LabelTest.java applet page

Can I handle an URL name or a file name transparently?

I found this information at Maeda Atusi's Java(tm)Tips. (In Japanese)

When you want to process both of a file name or an URL name transparently, the URL context helps you.

  URL context = new URL("file:" + new File(".").getAbsolutePath());
  URL url     = new URL(context, fileOrUrl);

In this case, the fileOrUrl is interpreted under the context. Then, you do not need to care a fileOrUrl is a filename or an URL.

  % java URLFile index.html
  url = file:/an/absolute/path/index.html
  protocol = file

  % java URLFile http://www/index.html
  url = http://www/index.html
  protocol = http