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# Quick Start

Welcome to BeanShell. This is a crash course to get you going. We'll leave out many important options and details. Please see the rest of the user's guide for more information.

## Download and Run BeanShell

Download the latest JAR file from http://www.beanshell.org and start up BeanShell either in the graphical desktop mode or on the command line.

If you just want to start playing around you may be able to launch the BeanShell desktop by simply double clicking on the BeanShell JAR file. More generally however you'll want to add the jar to your classpath so that you can work with your own classes and applications easily.

To do this you can either drop the BeanShell JAR file into your Java extensions folder or add it to your classpath. (Important: If you put BeanShell in the extensions folder and wish to use it with BSF applications like Jakarta Ant you must install the bsf.jar in the same location).

    To install as an extension place the bsh.jar file in your
    $JAVA_HOME/jre/lib/ext folder.  (OSX users: place the bsh.jar in
    /Library/Java/Extensions or ~/Library/Java/Extensions for individual users.)

    Or add BeanShell to your classpath like this:

    unix:     export CLASSPATH=$CLASSPATH:bsh-xx.jar
    windows:  set classpath=%classpath%;bsh-xx.jar

Tip: You can modify the classpath from within BeanShell using the addClassPath() and setClassPath() commands.

You can then run BeanShell in either a GUI or command line mode:

        java bsh.Console       // run the graphical desktop
    or
        java bsh.Interpreter   // run as text-only on the command line
    or
        java bsh.Interpreter filename [ args ] // run script file

It's also possible to call BeanShell from within your own Java applications, to reach it in a remote server mode for debugging, to use it as a servlet, or even in an applet. See "BeanShell Modes of Operation" for more details.

## The BeanShell GUI

The BeanShell GUI desktop is meant to allow some experimentation with the features of BeanShell. It is not intended to be a replacement for a full featured IDE. Please check out the jEdit editor for an example of a full featured development environment based in part on BeanShell scripting capabilities.

Upon starting the BeanShell in GUI mode a console window will open. By right clicking on the desktop background you can open additional console windows and other tools such as a simple class browser.

Each console window runs a separate instance of the BeanShell interpreter. The graphical console supports basic command history, line editing, cut and paste, and even class and variable name completion. From the console you can open a simple editor window. In it you can write scripts and use the 'eval' option to evaluate the text in the attached console's workspace or a new workspace.

## Java Statements and Expressions

BeanShell understands standard Java statements, expressions, and method declarations. Statements and expressions are all of the normal things that you'd say inside a Java method such as variable declarations and assignments, method calls, loops, and conditionals.

You can use these exactly as they would appear in Java, however in BeanShell you also have the option of working with "loosely typed" variables. That is, you can simply omit the types of variables that you use (both primitives and objects). BeanShell will only signal an error if you attempt to misuse the actual type of the variable.

Here are some examples:

    foo = "Foo";
    four = (2 + 2)*2/2;
    print( foo + " = " + four );  // print() is a BeanShell command

    // Do a loop
    for (i=0; i<5; i++)
        print(i);

    // Pop up a frame with a button in it
    button = new JButton( "My Button" );
    frame = new JFrame( "My Frame" );
    frame.getContentPane().add( button, "Center" );
    frame.pack();
    frame.setVisible(true);

## Useful BeanShell Commands

In the previous example we used a convenient "built-in" BeanShell command called print(), to display values. print() does pretty much the same thing as System.out.println() except that it insures that the output always goes to the command line. print() also displays some types of objects (such as arrays) more verbosely than Java would. Another related command is show(), which toggles on and off automatic display of the result of every line you type.

Here are a few other examples of BeanShell commands:

- source(), run() - Read a bsh script into this interpreter, or run it in a new interpreter
- frame() - Display a GUI component in a Frame or JFrame.
- load(), save() - Load or save serializable objects to a file.
- cd(), cat(), dir(), pwd(), etc. - Unix-like shell commands
- exec() - Run a native application
- javap() - Print the methods and fields of an object, similar to the output of the Java javap command.
- setAccessibility() - Turn on unrestricted access to private and protected components.

See the complete list of BeanShell Commands for more information.

Tip: BeanShell commands are not really "built-in" but are simply BeanShell scripts that are automatically loaded from the classpath. You can add your own scripts to the classpath to extend the basic command set.

## Scripted Methods

You can declare and use methods in BeanShell just as you would in a Java class.

    int addTwoNumbers( int a, int b ) {
        return a + b;
    }

    sum = addTwoNumbers( 5, 7 );  // 12

Bsh methods may also allow dynamic (loose) argument and return types.

    add( a, b ) {
        return a + b;
    }

    foo = add(1, 2);            // 3
    foo = add("Oh", " baby");   // "Oh baby"

## Implementing Interfaces

Note: implementing arbitrary interfaces requires BeanShell be run under a Java 1.3 or higher environment.

You can use the standard Java anonymous inner class syntax to implement an interface type with a script. For example:

    ActionListener scriptedListener = new ActionListener() {
        actionPerformed( event ) { ... }
    }

You don't have to script all of the methods of an interface. You can opt to script only those that you intend to call if you want to. The calling code will simply throw an exception if it tries to invoke a method that isn't defined. If you wish to override the behavior of a large number of methods - say to produce a "dummy" adapter for logging - you can implement a special method signature: invoke(name, args) in your scripted object. The invoke() method is called to handle any undefined method invocations:

    ml = new MouseListener() {
        mousePressed( event ) { ... }
        // handle the rest
        invoke( name, args ) { print("Method: "+name+" invoked!");
    }

## Scripted Objects

In BeanShell, as in JavaScript and Perl, method "closures" allow you to create scripted objects. You can turn the results of a method call into an object reference by having the method return the special value this. You can then use the reference to refer to any variables set during the method call. Useful objects need methods of course, so in BeanShell scripted methods may also contain methods at any level. For example:

    foo() {
        print("foo");
        x=5;

        bar() {
            print("bar");
        }

        return this;
    }

    myfoo = foo();    // prints "foo"
    print( myfoo.x ); // prints "5"
    myfoo.bar();      // prints "bar"

If this "closure" thing seems strange to don't worry. It's just an evolutionary step that languages acquired along the path to Objects. Please see the user's manual for a more thorough explanation.

Within your scripts, BeanShell scripted objects (i.e. any 'this' type reference like myFoo in the previous example) can automatically implement any Java interface type. When Java code calls methods on the interface the corresponding scripted methods will be invoked to handle them. BeanShell will automatically "cast" your scripted object when you attempt to pass it as an argument to a method that takes an interface type. For passing script references outside of BeanShell, you can perform an explicit cast where necessary. Please see the user manual for full details.

## Calling BeanShell From Your Application

You can evaluate text and run scripts from within your application by creating an instance of the BeanShell interpreter and using the eval() or source() commands. You may pass in variable references to objects you wish to use in scripts via the set() method and retrieve results with the get() method.

    import bsh.Interpreter;

    Interpreter i = new Interpreter();  // Construct an interpreter
    i.set("foo", 5);                    // Set variables
    i.set("date", new Date() );

    Date date = (Date)i.get("date");    // retrieve a variable

    // Eval a statement and get the result
    i.eval("bar = foo*10");
    System.out.println( i.get("bar") );

    // Source an external script file
    i.source("somefile.bsh");

Tip: In the above example the Interpreter's eval() method also returned the value of bar as the result of the evaluation.

## Conclusion

We hope this brief introduction gets you started. Please see the full user manual for more details. Please consult the mailing list archives for more useful information. http://www.beanshell.org/

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