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Quick Start

Download and Run BeanShell

If your project is built with Maven or Gradle you can skip the download and pull BeanShell from Maven Central instead, as io.github.beanshell:bsh:2.1.1.

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

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

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

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

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.

Scripted Methods

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

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

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

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");

Conclusion

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