Sample 1: using the JRE only (no configuration of the JVM) (Re: New candidate JEP: 454: Foreign Function & Memory API

[Rony G. Flatscher]

This sample should make the reader aware, that it is useful and helpful to use plain Java programs, 
commands with an installed JRE, without any need for any special configuration.

Once Java/JDK gets installed globally all processes have access to the appropriate "Java/JDK runtime 
environment (JRE)".

A globally installed JRE can be exploited in many ways.

One way, following the important property of Java's "once compiled, run everyhwere" and the 
excellent support of Java class libraries to abstract operating system dependent functionality in a 
portable manner it is very attractive to exploit Java/JDK in form of Java commands.

Here is a simple command that will list all installed font families on any computer, no matter 
whether it is Windows, Linux or macOS. As the font family names are output to standard output such a 
Java program can be exploited in pipes making it easy to use Java commands in shell programs.

Here the Java program ListFonts.java

    import java.awt.*;

    // demonstrate a simple Java command tool to list fonts available on the
    // user's platform to stdout to allow e..g integration with pipes
    public class ListFonts
    {
         public static void main (String args[])
         {
             listFonts();
         }

         // list font names to stdout: allows for making it available for piping
         public static void listFonts ()
         {
             for (String fn :
    GraphicsEnvironment.getLocalGraphicsEnvironment().getAvailableFontFamilyNames())
             {
                 System.out.println(fn);
             }
         }
    }

As simple as this Java program seems, it is an incredible time saver compared to programs in other 
programming languages!

The reason being simple: you compile that program once and can use it unchanged on all operating 
systems like Windows, Linux and macOS, via the JRE with its standard runtime Java class libraries.

It is a command that is easy to use, no configuration whatsoever necessary.

On my Windows machine the output of running:

    java ListFonts

is something like:

    Arial
    Arial Black
    Arial Narrow
    Arial Rounded MT Bold
    Bahnschrift
    Baskerville Old Face
    Bauhaus 93
    ... cut ...
    Wingdings
    Wingdings 2
    Wingdings 3
    Yu Gothic
    Yu Gothic Light
    Yu Gothic Medium
    Yu Gothic UI
    Yu Gothic UI Light
    Yu Gothic UI Semibold
    Yu Gothic UI Semilight
    ZWAdobeF

---

As this is a Java command that writes to stdout one can use it in a little script, e.g. to learn 
which "Gothic" fonts are installed on a particular machine:

On my Windows machine the output of running:

    java ListFonts | grep -i gothic

  is:

    Century Gothic
    Copperplate Gothic Bold
    Copperplate Gothic Light
    Franklin Gothic Book
    Franklin Gothic Demi
    Franklin Gothic Demi Cond
    Franklin Gothic Heavy
    Franklin Gothic Medium
    Franklin Gothic Medium Cond
    Malgun Gothic
    Malgun Gothic Semilight
    Microsoft NeoGothic
    MS Gothic
    MS PGothic
    MS UI Gothic
    Showcard Gothic
    Yu Gothic
    Yu Gothic Light
    Yu Gothic Medium
    Yu Gothic UI
    Yu Gothic UI Light
    Yu Gothic UI Semibold
    Yu Gothic UI Semilight

---

There are (even quite complex) Java programs that can serve as commands and used in pipes making it 
easy to exploit the functionality of the Java class libraries contained in the JRE on all operating 
system platforms. It is easy because it is easy to launch the Java programs as the JRE is available.

If the JRE gets updated by installing a bugfix or a newer Java/JDK all of the existing Java programs 
keep on running unchanged and uninterrupted.

It is easy to exploit Java in this manner and has been done for decades.

---rony

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