The JDK includes a program called javap , the Java Printer. Sun’s JDK version normally prints the outline of a class file -- a list of its methods and fields -- but can also print out the Java bytecodes or machine instructions. The Kaffe package did not include a version of javap, so I wrote one and contributed it (see Example 25-8). The Kaffe folk have expanded it somewhat, but it still works basically the same. My version doesn’t print the bytecodes; it behaves rather like Sun’s behaves when you don’t give theirs any command-line options.
The getFields( ) and getMethods( ) methods
return array of Field
and Method respectively; these are both in package
java.lang.reflect. I use a
Modifiers object to get details on the
permissions and storage
attributes of the fields and methods. In many implementations you can
bypass this, and simply call toString( )
in
each Field and Method object.
Doing it this way gives me a bit more control over the
formatting.
Example 25-8. MyJavaP.java
import java.io.*;
import java.util.*;
import java.lang.reflect.*;
/**
* JavaP prints structural information about classes.
* For each class, all public fields and methods are listed.
* "Reflectance" is used to look up the information.
*/
public class MyJavaP {
/** A "Modifier" object, to decode modifiers of fields/methods */
Modifier m = new Modifier( );
/** Simple main program, construct self, process each class name
* found in argv.
*/
public static void main(String[] argv) {
MyJavaP pp = new MyJavaP( );
if (argv.length == 0) {
System.err.println("Usage: javap className [...]");
System.exit(1);
} else for (int i=0; i<argv.length; i++)
pp.doClass(argv[i]);
}
/** Format the fields and methods of one class, given its name.
*/
protected void doClass(String className) {
try {
Class c = Class.forName(className);
System.out.println(m.toString(c.getModifiers( )) + ' ' + c + " {");
int i, mods;
Field fields[] = c.getFields( );
for (i = 0; i < fields.length; i++) {
if (!m.isPrivate(fields[i].getModifiers( ))
&& !m.isProtected(fields[i].getModifiers( )))
System.out.println(" " + fields[i]);
}
Method methods[] = c.getMethods( );
for (i = 0; i < methods.length; i++) {
if (!m.isPrivate(methods[i].getModifiers( ))
&& !m.isProtected(methods[i].getModifiers( )))
System.out.println(" " + methods[i]);
}
} catch (ClassNotFoundException e) {
System.err.println("Error: Class " +
className + " not found!");
} catch (Exception e) {
System.err.println(e);
} finally {
System.out.println("}");
}
}
}