macro-tips-BeanShell.html

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<html><head><meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1"><title>Advanced BeanShell Techniques</title><meta name="generator" content="DocBook XSL Stylesheets V1.65.1"><link rel="home" href="index.html" title="jEdit 4.2 User's Guide"><link rel="up" href="macro-tips.html" title="Chapter 15. Macro Tips and Techniques"><link rel="previous" href="scripts-command-line.html" title="Running Scripts from the Command
Line"><link rel="next" href="macro-tips-debugging.html" title="Debugging Macros"></head><body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">Advanced BeanShell Techniques</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="scripts-command-line.html">Prev</a> </td><th width="60%" align="center">Chapter 15. Macro Tips and Techniques</th><td width="20%" align="right"> <a accesskey="n" href="macro-tips-debugging.html">Next</a></td></tr></table><hr></div><div class="sect1" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="macro-tips-BeanShell"></a>Advanced BeanShell Techniques</h2></div></div><div></div></div><p>
  BeanShell has a few advanced features that we haven't mentioned yet.
  They will be discussed in this section.
</p><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="macro-tips-BeanShell-convenience"></a>BeanShell's Convenience Syntax</h3></div></div><div></div></div><p>
  We noted earlier that BeanShell syntax does not require that variables
  be declared or defined with their type, and that variables that are
  not typed when first used can have values of differing types assigned
  to them. In addition to this &#8220;<span class="quote">loose</span>&#8221; syntax, BeanShell
  allows a &#8220;<span class="quote">convenience</span>&#8221; syntax for dealing with the
  properties of JavaBeans.  They may be accessed or set as if they were
  data members. They may also be accessed using the name of the property
  enclosed in quotation marks and curly brackets.  For example, the following
  statement are all equivalent, assuming <tt class="varname">btn</tt> is
  a <tt class="classname">JButton</tt> instance:
</p><div class="informalexample"><table border="0" bgcolor="#E0E0E0"><tr><td><pre class="programlisting">b.setText("Choose");
b.text = "Choose";
b{"text"} = "Choose";
</pre></td></tr></table></div><p>
  The last form can also be used to access a key-value pair of a
  <tt class="classname">Hashtable</tt> object.
</p></div><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="macro-tips-BeanShell-keywords"></a>Special BeanShell Keywords</h3></div></div><div></div></div><p>
  BeanShell uses special keywords to refer to variables or methods defined in
  the current or an enclosing block's scope:
</p><div class="itemizedlist"><ul type="disc"><li><p>
      The keyword <tt class="function">this</tt> refers to the current scope.
    </p></li><li><p>
      The keyword <tt class="function">super</tt> refers to the immediately
      enclosing scope.
    </p></li><li><p>
      The keyword <tt class="function">global</tt> refers to the top-level
      scope of the macro script.
    </p></li></ul></div><p>
  The following script illustrates the use of these keywords:
</p><div class="informalexample"><table border="0" bgcolor="#E0E0E0"><tr><td><pre class="programlisting">a = "top\n";
foo() {
    a = "middle\n";
    bar() {
        a = "bottom\n";
        textArea.setSelectedText(global.a);
        textArea.setSelectedText(super.a);
        // equivalent to textArea.setSelectedText(this.a):
        textArea.setSelectedText(a);
    }

    bar();
}
foo();</pre></td></tr></table></div><p>
  When the script is run, the following text is inserted in the current
  buffer:
</p><table border="0" bgcolor="#E0E0E0"><tr><td><pre class="screen">top
middle
bottom</pre></td></tr></table></div><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="macro-tips-BeanShell-class"></a>Implementing Classes and Interfaces</h3></div></div><div></div></div><p>
  As discussed in the macro example in <a href="dialog-macro.html" title="Chapter 14. A Dialog-Based Macro">Chapter 14, <i>A Dialog-Based Macro</i></a>, scripted objects can implicitly implement Java
  interfaces such as <tt class="classname">ActionListener</tt>. For example:
</p><table border="0" bgcolor="#E0E0E0"><tr><td><pre class="programlisting">myRunnable() {
    run() {
        System.out.println("Hello world!");
    }
    
    return this;
}

Runnable r = myRunnable();
new Thread(r).start();</pre></td></tr></table><p>
  Frequently it will not be necessary to implement all of the methods of
  a particular interface in order to specify the behavior of a scripted
  object. To prevent BeanShell from throwing exceptions for missing interface methods, implement the <tt class="function">invoke()</tt> method,
  which is called when an undefined method is invoked on a scripted
  object. Typically, the implementation of this method will do nothing,
  as in the following example:
</p><div class="informalexample"><table border="0" bgcolor="#E0E0E0"><tr><td><pre class="programlisting">invoke(method, args) {}</pre></td></tr></table></div><p>
  In addition to the implicit interface definitions described above,
  BeanShell permits full-blown classes to be defined. Indeed, almost any Java class definition should work in BeanShell:
</p><table border="0" bgcolor="#E0E0E0"><tr><td><pre class="programlisting">class Cons {
    // Long-live LISP!
    Object car;
    Object cdr;

    rplaca(Object car) {
        this.car = car;
    }

    rplacd(Object cdr) {
        this.cdr = cdr;
    }
}</pre></td></tr></table></div></div><div class="navfooter"><hr><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="scripts-command-line.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="macro-tips.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="macro-tips-debugging.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">Running Scripts from the Command
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