зеркало из https://github.com/mozilla/pjs.git
Added Compatibility discussion.
Tweaked Mac build instructions.
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fur
Родитель
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Коммит
444c8ac8b5
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@ -7,20 +7,11 @@
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</HEAD>
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<BODY>
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<CENTER>
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<H2>
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<FONT COLOR="#CC0000"><FONT SIZE=+3>WARNING:</FONT></FONT></H2></CENTER>
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<CENTER>
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<H2>
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<FONT COLOR="#CC0000">This document is a skeleton, still <BR>
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very much under construction.</FONT></H2></CENTER>
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<H2>
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Introduction</H2>
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This is the README file for the JavaScript LiveConnect implementation.
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It consists of build conventions and instructions, source code conventions,
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a design walk-through, and a brief file-by-file description of the source.
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and a brief file-by-file description of the source.
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<P>This document assumes basic familiarity with JSRef, the reference implementation
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of JavaScript, and with the LiveConnect technology (LiveConnect allows
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@ -39,6 +30,117 @@ Interface (JNI), as specified by JavaSoft. It then compiles a small
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that can be used interactively and with test scripts.
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<P><I>Scott Furman, 4/8/98</I>
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<H2>
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Compatibility</H2>
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Unlike this release, all previous versions of LiveConnect appeared only
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as a component of Netscape Navigator, not as a standalone module.
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The variants of LiveConnect that appeared in Navigator versions 3.x and
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4.x all behave much the same, modulo bugs. For brevity we refer to
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this classic version of LiveConnect as "LC1" and this most recent release
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as "LC2". The following incompatibilities with LC1 are known:
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<UL>
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<LI>
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As in LC1, JavaScript objects appear to Java as instances of <I>netscape.javascript.JSObject</I>.
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In LC1, two <I>JSObject</I>'s could be tested for equality, i.e. to see
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if they refer to the same instance, by using the `==' operator. Instead,
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developers must now use the <TT>equals()</TT>method of <I>netscape.javascript.JSObject</I>
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for comparison, a method that overrides <TT>java.lang.Object.equals()</TT>.
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Using <TT>equals()</TT> instead of `==' should work the same on both LC1
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and LC2. <BR>
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<BR>
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It is not possible to replicate the identity behavior of the `==' operator
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that LC1 provides without the use of "weak" references, i.e. references
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that do not contribute to making a Java object reachable for purposes of
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garbage collection, but which nonetheless allow reference to an object
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as long as it is reachable by other means. The use of weak references
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is not portable, however. It is not part of the JNI or the JDK and
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it is not provided on all JVMs. The JDK1.2 release will include standard
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support for weak references.<BR>
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<BR></LI>
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<LI>
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It's possible that, in a set of overloaded Java methods, more than one
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is compatible with the types of the actual arguments in a call from JavaScript
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via LiveConnect. LC1 resolved these ambiguities in a simplistic manner,
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by simply invoking whatever method was enumerated first by the JVM.
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The enumeration order of reflected methods using <I>java.lang.reflect</I>
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is not specified by Sun and may differ among vendor's JVMs, i.e. enumeration
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could be in order of classfile appearance, hashtable order, etc.
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With the Netscape and Sun JVMs, it is possible to change the behavior of
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an LC1 program by changing the order that Java methods appear in a source
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file, thus changing the method enumeration order. Hence, the Java
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method chosen when there is more than one compatible method may vary depending
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on the JVM.<BR>
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<BR>
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A future release of LiveConnect will provide a new algorithm for overloaded
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Java method resolution that is both independent of the JVM used and more
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likely than LC1 to invoke the method that the developer expects.<BR>
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<BR></LI>
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<LI>
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There are several minor changes in error handling to make LiveConnect more
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conformant to ECMAScript. These include, for example, making any
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attempt to delete JavaObject, JavaClass or JavaPackage properties fail
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silently, rather than causing an error. Also, some error messages
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have been changed to be more informative. These changes should generally
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be backward-compatible with LC1 because few programs that use LiveConnect
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will depend on the exact behavior of LiveConnect when handling errors.</LI>
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</UL>
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<H2>
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New Features</H2>
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Several minor features have been added to this release of LiveConnect.
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These features were not available in the versions of LiveConnect that were
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integrated with Netscape Naviagtor versions 4.x and earlier.
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<BR>
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<BLOCKQUOTE>
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<LI>
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The Java methods of <I>java.lang.Object</I> are now invokeable methods
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of <TT><FONT SIZE=+1>JavaArray</FONT></TT> objects, matching the behavior
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of arrays when accessed from Java<I>.</I> (Java arrays are a subclass
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of <I>java.lang.Object</I>.) For example, Java's <TT><FONT SIZE=+1>getClass()</FONT></TT>
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and <TT><FONT SIZE=+1>hashCode()</FONT></TT> methods can now be called
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on <TT><FONT SIZE=+1>JavaArray</FONT></TT> objects. (In prior versions
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of LiveConnect, the methods of <I>java.lang.Object</I> were only inherited
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by non-array Java objects.)</LI>
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<P>Note that this change has caused the string representation of JavaArray
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objects to change. Previously, the JavaArray toString() method always
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printed "<TT><FONT SIZE=+1>[object JavaArray]"</FONT></TT> for all <TT><FONT SIZE=+1>JavaArray</FONT></TT>'s.
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Now, the Java <TT><FONT SIZE=+1>java.lang.Object.toString()</FONT></TT>
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method is called to convert JavaArray objects to strings, just as with
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other, non-array Java objects that are accessible via LiveConnect.
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<TT><FONT SIZE=+1>java.lang.Object.toString()</FONT></TT>is defined in
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the <I>Java Language Specification</I> to return the value of the following
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expression:
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<P><TT><FONT SIZE=-1>getClass().getName() + '@' + Integer.toHexString(hashCode())</FONT></TT>
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<BR>
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<LI>
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A one-character string is now an acceptable match for an argument to a
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Java method of type <TT><FONT SIZE=+1>char</FONT></TT>. (In earlier
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versions of LiveConnect, the only acceptable match for a <TT><FONT SIZE=+1>char</FONT></TT>
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had to be a JavaScript value that was convertible to a number.) For
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example, the following is now possible:</LI>
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<P><TT><FONT SIZE=-1>c = new java.lang.Character("F")</FONT></TT>
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<BR>
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<LI>
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A JavaClass object is now an acceptable match for an argument to a Java
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method of type <I>java.lang.Class</I>. For example, you can now write:</LI>
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<P><TT><FONT SIZE=-1>java.lang.reflect.Array.newInstance(java.lang.String,
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3)</FONT></TT>
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<P>instead of the more verbose:
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<P><TT><FONT SIZE=-1>jls = java.lang.Class.forName("java.lang.String")</FONT></TT>
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<BR><TT><FONT SIZE=-1>java.lang.reflect.Array.newInstance(jls, 3)</FONT></TT>
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<BR> </BLOCKQUOTE>
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<H2>
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Build conventions</H2>
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Update your JVM's <TT><FONT SIZE=+1>CLASSPATH</FONT></TT> to point to the
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@ -46,14 +148,17 @@ Update your JVM's <TT><FONT SIZE=+1>CLASSPATH</FONT></TT> to point to the
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you do not, LiveConnect will still operate but with the limitation that
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JS objects may not be passed as arguments of Java methods and it will not
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be possible to call from Java into JavaScript, i.e. the <I>netscape.javascript.JSObject</I>
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class will be inaccessible. If your <TT><FONT SIZE=+1>CLASSPATH</FONT></TT>
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class will be inaccessible. Another downside of operating without
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these classes is that Java error messages will not include a Java stack
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trace, when one is available. If your <TT><FONT SIZE=+1>CLASSPATH</FONT></TT>
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is set improperly, you will see a message like, "<TT><FONT SIZE=+1>initialization
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error: Can't load class netscape/javascript/JSObject</FONT></TT>" when
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starting a LiveConnect debug build.
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<P>To enable multi-threaded execution, define the <TT><FONT SIZE=+1>JS_THREADSAFE</FONT></TT>
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cpp macro and flesh out the stubs and required headers in jslock.c/.h.
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See the JS API docs for more. JSRef must also be built with <TT><FONT SIZE=+1>JS_THREADSAFE</FONT></TT>.
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<P>By default, LiveConnect is not re-entrant. To enable multi-threaded
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execution, define the <TT><FONT SIZE=+1>JS_THREADSAFE</FONT></TT> cpp macro
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and flesh out the stubs and required headers in jslock.c/.h. See
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the JS API docs for more. JSRef must also be built with <TT><FONT SIZE=+1>JS_THREADSAFE</FONT></TT>.
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<BR>
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<UL><B>Windows</B>
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<UL>
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@ -87,54 +192,48 @@ in the JDK's bin directory.</LI>
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<LI>
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Use any Java compiler to compile the java source files in the <TT><FONT SIZE=+1>js/ref/liveconnect/classes/netscape/javascript</FONT></TT>
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directory.<BR>
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<BR></LI>
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directory.</LI>
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</UL>
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<BR>
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<B>Mac OS</B>
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<UL>
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<LI>Using CodeWarrior Pro 3 is recommended. CodeWarrior
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Pro 2 should work but has not been tested. The
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CodeWarrior project files are <TT><FONT
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SIZE="+1">js/ref/liveconnect/macbuild/LiveConnect.mcp</FONT></TT>,
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<TT><FONT
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SIZE="+1">js/ref/liveconnect/macbuild/LiveConnectShell.mcp</FONT></TT>,
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and<TT><FONT SIZE="+1"> js/ref/macbuild/JSRef.mcp</FONT></TT>.
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<LI>
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Using CodeWarrior Pro 3 is recommended. With some modifications,
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the project files can be made to work with CodeWarrior Pro 2. The
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CodeWarrior project files are <TT><FONT SIZE=+1>js/ref/liveconnect/macbuild/LiveConnect.mcp</FONT></TT>,
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<TT><FONT SIZE=+1>js/ref/liveconnect/macbuild/LiveConnectShell.mcp</FONT></TT>,
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and<TT><FONT SIZE=+1> js/ref/macbuild/JSRef.mcp</FONT></TT>.</LI>
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<LI>Install Apple's JVM, MRJ 2.0 (or later),and the
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<A HREF="ftp://dev.apple.com/devworld/Java/MRJSDK2.0.1EarlyAccess4.hqx">MRJ
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SDK v2.0.1ea4</A>.
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<LI>
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Install Apple's JVM, MRJ 2.0 (or later), and the <A HREF="ftp://dev.apple.com/devworld/Java/MRJSDK2.0.1EarlyAccess4.hqx">MRJ
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SDK v2.0.1ea4</A>. Note: You do not need to install MRJ if you are
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running a recent version of MacOS 8, since it is shipped with the OS.</LI>
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<LI>Copy the folders CIncludes & Libraries from
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Interfaces&Libraries to <TT><FONT
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SIZE="+1">js/ref/liveconnect/macbuild/JavaSession</FONT></TT>.
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<LI>
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Copy the folders CIncludes & Libraries from the SDK's Interfaces&Libraries
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directory to <TT><FONT SIZE=+1>js/ref/liveconnect/macbuild/JavaSession</FONT></TT>.</LI>
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<LI>Build the JavaScript test application, <TT><FONT
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SIZE="+1">JSRef</FONT></TT>, with <TT><FONT
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SIZE="+1">js/ref/macbuild/JSRef.mcp</FONT></TT>.
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<LI>
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Build the JavaScript test application, <TT><FONT SIZE=+1>JSRef</FONT></TT>,
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with <TT><FONT SIZE=+1>js/ref/macbuild/JSRef.mcp</FONT></TT>.</LI>
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<LI>Build the LiveConnect test application, <TT><FONT
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SIZE="+1">LiveConnectShell</FONT></TT>, with <TT><FONT
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SIZE="+1">js/ref/liveconnect/macbuild/LiveConnectShell.mcp</FONT></TT>.
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<LI>Build <TT><FONT SIZE="+1">liveconnect.jar</FONT></TT> with
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<TT><FONT
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SIZE="+1">js/ref/liveconnect/macbuild/LiveConnect.mcp</FONT></TT>.
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<LI>Make an alias to <TT><FONT
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SIZE="+1">liveconnect.jar</FONT></TT> and place it in
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"<TT><FONT SIZE="+1">{SystemFolder}Extensions:MRJ
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Libraries:MRJClasses</FONT></TT>".<BR>
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<BR>
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<LI>
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Build the LiveConnect test application, <TT><FONT SIZE=+1>LiveConnectShell</FONT></TT>,
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with <TT><FONT SIZE=+1>js/ref/liveconnect/macbuild/LiveConnectShell.mcp</FONT></TT>.</LI>
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<LI>
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Build <TT><FONT SIZE=+1>liveconnect.jar</FONT></TT> with <TT><FONT SIZE=+1>js/ref/liveconnect/macbuild/LiveConnect.mcp</FONT></TT>.</LI>
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<LI>
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Make an alias to <TT><FONT SIZE=+1>liveconnect.jar</FONT></TT> and place
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it in "<TT><FONT SIZE=+1>{SystemFolder}Extensions:MRJ Libraries:MRJClasses</FONT></TT>".<BR>
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<BR></LI>
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</UL>
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<B>Unix</B>
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<UL>
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<LI>
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<FONT COLOR="#FF0000">No Makefiles created yet</FONT></LI>
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<FONT COLOR="#FF0000">No Makefiles have been completed yet. These
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notes are a work in progress.</FONT></LI>
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<LI>
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Use vendor cc or gcc (ftp://prep.ai.mit.edu/pub/gnu) for compiling,
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@ -215,12 +314,9 @@ be used after the return type and before the function name).</LI>
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The LiveConnect API</H2>
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All public LiveConnect entry points and callbacks are documented in jsjava.h,
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the header file that exports those functions.
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<H2>
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Design walk-through</H2>
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<BR>
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<H2>
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File walk-through</H2>
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File Walk-through</H2>
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<TABLE BORDER=3 CELLSPACING=0 CELLPADDING=4 >
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<TR>
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