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  1<html><head><meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1"><title>The Mandatory First Example</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-basics.html" title="Chapter 13. Macro Basics"><link rel="previous" href="single-macros.html" title="Single Execution Macros"><link rel="next" href="predefined-variables.html" title="Predefined Variables in BeanShell"></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">The Mandatory First Example</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="single-macros.html">Prev</a> </td><th width="60%" align="center">Chapter 13. Macro Basics</th><td width="20%" align="right"> <a accesskey="n" href="predefined-variables.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="first-example"></a>The Mandatory First Example</h2></div></div><div></div></div><div class="informalexample"><table border="0" bgcolor="#E0E0E0"><tr><td><pre class="programlisting">Macros.message(view, "Hello world!");</pre></td></tr></table></div><p>
  2   Running this one line script causes jEdit to display a message
  3   box (more precisely, a <tt class="classname">JOptionPane</tt> object) with
  4   the traditional beginner's message and an <span><b class="guilabel">OK</b></span> button.
  5   Let's see what is happening here.
  6  </p><p>
  7   This statement calls a static method (or function) named
  8   <tt class="function">message</tt> in jEdit's <a href="../api/org/gjt/sp/jedit/Macros.html" target="_top">Macros</a>
  9   class. If you don't know anything about classes or static methods or
 10   Java (or C++, which employs the same concept), you will need to gain
 11   some understanding of a few terms. Obviously this is not the place for
 12   academic precision, but if you are entirely new to object-oriented
 13   programming, here are a few skeleton ideas to help you with BeanShell.
 14  </p><div class="itemizedlist"><ul type="disc"><li><p>
 15     An <i class="glossterm">object</i> is a collection of data that can be
 16     initialized, accessed and manipulated in certain defined ways.
 17    </p></li><li><p>
 18     A <i class="glossterm">class</i> is a specification of what data an object
 19     contains and what methods can be used to work with the data. A Java
 20     application consists of one or more classes (in the case of jEdit ,over
 21     600 classes) written by the programmer that defines the application's
 22     behavior. A BeanShell macro uses these classes, along with built-in
 23     classes that are supplied with the Java platform, to define its own
 24     behavior.
 25    </p></li><li><p>
 26     A <i class="glossterm">subclass</i> (or child class) is a class which
 27     uses (or &#8220;<span class="quote">inherits</span>&#8221;) the data and methods of its parent
 28     class along with additions or modifications that alter the subclass's
 29     behavior.  Classes are typically organized in hierarchies of parent
 30     and child classes to organize program code, to define common
 31     behavior in shared parent class code, and to specify the types of
 32     similar behavior that child classes will perform in their own specific ways.
 33    </p></li><li><p>
 34     A <i class="glossterm">method</i> (or function) is a procedure that works
 35     with data in a particular object, other data (including other objects)
 36     supplied as <i class="glossterm">parameters</i>, or both. Methods
 37     typically are applied to a particular object which is an
 38     <i class="glossterm">instance</i> of the class to which the method
 39     belongs.
 40    </p></li><li><p>
 41     A <i class="glossterm">static method</i> differs from other methods
 42     in that it does not deal with the data in a particular object but is
 43     included within a class for the sake of convenience.
 44    </p></li></ul></div><p>
 45   Java has a rich set of classes defined as part of the Java platform.
 46   Like all Java applications, jEdit is organized as a set of classes that
 47   are themselves derived from the Java platform's classes. We will refer
 48   to <i class="firstterm">Java classes</i> and <i class="firstterm">jEdit
 49   classes</i> to make this distinction. Some of jEdit's classes
 50   (such as those dealing with regular expressions and XML) are derived
 51   from or make use of classes in other open-source Java packages. Except
 52   for BeanShell itself, we won't be discussing them in this guide.
 53  </p><p>
 54   In our one line script, the static method
 55   <tt class="function">Macros.message()</tt> has two parameters because that is
 56   the way the method is defined in the <a href="../api/org/gjt/sp/jedit/Macros.html" target="_top">Macros</a>
 57   class. You must specify both parameters when you call the function. The
 58   first parameter, <i class="parameter"><tt>view</tt></i>, is a variable naming
 59   the current, active <a href="../api/org/gjt/sp/jedit/View.html" target="_top">View</a> object. Information
 60   about pre-defined variables can be found in <a href="predefined-variables.html" title="Predefined Variables in BeanShell">the section called &#8220;Predefined Variables in BeanShell&#8221;</a>.
 61  </p><p>
 62   The second parameter, which appears to be quoted text, is a
 63   <i class="glossterm">string literal</i> - a sequence of characters of
 64   fixed length and content. Behind the scenes, BeanShell and Java take
 65   this string literal and use it to create a <tt class="classname">String</tt>
 66   object. Normally, if you want to create an object in Java or BeanShell,
 67   you must construct the object using the <tt class="function">new</tt> keyword
 68   and a <i class="firstterm">constructor</i> method that is part of the
 69   object's class. We'll show an example of that later. However, both Java
 70   and BeanShell let you use a string literal anytime a method's parameter
 71   calls for a <tt class="classname">String</tt>.
 72  </p><p>
 73   If you are a Java programmer, you might wonder about a few things
 74   missing from this one line program. There is no class definition, for
 75   example. You can think of a BeanShell script as an implicit definition
 76   of a <tt class="function">main()</tt> method in an anonymous class. That is
 77   in fact how BeanShell is implemented; the class is derived from
 78   a BeanShell class called <a href="../api/bsh/XThis.html" target="_top">XThis</a>. If you
 79   don't find that helpful, just think of a script as one or more blocks of
 80   procedural statements conforming to Java syntax rules. You will also get
 81   along fine (for the most part) with C or C++ syntax if you leave out
 82   anything to do with pointers or memory management - Java and BeanShell
 83   do not have pointers and deal with memory management automatically.
 84  </p><p>
 85    Another missing item from a Java perspective is a
 86    <tt class="function">package</tt> statement. In Java, such a statement is
 87    used to bundle together a number of files so that their classes become
 88    visible to one another. Packages are not part of BeanShell,
 89    and you don't need to know anything about them to write
 90    BeanShell macros.
 91  </p><p>
 92    Finally, there are no <tt class="function">import</tt> statements in this
 93    script. In Java, an <tt class="function">import</tt> statement makes public
 94    classes from other packages visible within the file in which the
 95    statement occurs without having to specify a fully
 96    qualified class name. Without an import statement or a fully qualified
 97    name, Java cannot identify most classes using a single name as an identifier.
 98  </p><p>
 99   jEdit automatically imports a number of commonly-used packages into the
100   namespace of every BeanShell script. Because of this, the script output
101   of a recorded macro does not contain <tt class="function">import</tt>
102   statements. For the same reason, most BeanShell scripts you write will
103   not require <tt class="function">import</tt> statements.
104  </p><p>
105    Java requires <tt class="literal">import</tt> statement to be located
106    at the beginning of a source file. BeanShell allows you to place
107    <tt class="literal">import</tt>
108    statements anywhere in a script, including inside a block of
109    statements. The <tt class="literal">import</tt> statement will cover all names
110    used following the statement in the enclosing block.
111  </p><p>
112    If you try to use a class that is not imported without its
113    fully-qualified name, the BeanShell interpreter will complain with an
114    error message relating to the offending line of code.
115  </p><div class="sidebar"><p>
116    Here is the full list of packages automatically imported by jEdit:
117   </p><table border="0" bgcolor="#E0E0E0"><tr><td><pre class="programlisting">java.awt
138org.gjt.sp.util</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="single-macros.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="macro-basics.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="predefined-variables.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">Single Execution Macros </td><td width="20%" align="center"><a accesskey="h" href="index.html">Home</a></td><td width="40%" align="right" valign="top"> Predefined Variables in BeanShell</td></tr></table></div></body></html>