Java Cookbook

Printing Class Information

Problem

You want to print all the information about a class, similar to the way javap does.

Solution

Get a Class object, call its getFields( ) and getMethods( ), and print the results.

Discussion

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, ...