ShowClass.java Source code

Introduction

Here is the source code for ShowClass.java

Source

/*
 * Copyright (c) 2004 David Flanagan.  All rights reserved.
 * This code is from the book Java Examples in a Nutshell, 3nd Edition.
 * It is provided AS-IS, WITHOUT ANY WARRANTY either expressed or implied.
 * You may study, use, and modify it for any non-commercial purpose,
 * including teaching and use in open-source projects.
 * You may distribute it non-commercially as long as you retain this notice.
 * For a commercial use license, or to purchase the book, 
 * please visit http://www.davidflanagan.com/javaexamples3.
 */
//package je3.reflect;
import java.lang.reflect.Constructor;
import java.lang.reflect.Field;
import java.lang.reflect.Member;
import java.lang.reflect.Method;
import java.lang.reflect.Modifier;

/** A program that displays a class synopsis for the named class */
public class ShowClass {
    /** The main method. Print info about the named class */
    public static void main(String[] args) throws ClassNotFoundException {
        Class c = Class.forName(args[0]);
        print_class(c);
    }

    /**
     * Display the modifiers, name, superclass and interfaces of a class or
     * interface. Then go and list all constructors, fields, and methods.
     */
    public static void print_class(Class c) {
        // Print modifiers, type (class or interface), name and superclass.
        if (c.isInterface()) {
            // The modifiers will include the "interface" keyword here...
            System.out.print(Modifier.toString(c.getModifiers()) + " " + typename(c));
        } else if (c.getSuperclass() != null) {
            System.out.print(Modifier.toString(c.getModifiers()) + " class " + typename(c) + " extends "
                    + typename(c.getSuperclass()));
        } else {
            System.out.print(Modifier.toString(c.getModifiers()) + " class " + typename(c));
        }

        // Print interfaces or super-interfaces of the class or interface.
        Class[] interfaces = c.getInterfaces();
        if ((interfaces != null) && (interfaces.length > 0)) {
            if (c.isInterface())
                System.out.print(" extends ");
            else
                System.out.print(" implements ");
            for (int i = 0; i < interfaces.length; i++) {
                if (i > 0)
                    System.out.print(", ");
                System.out.print(typename(interfaces[i]));
            }
        }

        System.out.println(" {"); // Begin class member listing.

        // Now look up and display the members of the class.
        System.out.println("  // Constructors");
        Constructor[] constructors = c.getDeclaredConstructors();
        for (int i = 0; i < constructors.length; i++)
            // Display constructors.
            print_method_or_constructor(constructors[i]);

        System.out.println("  // Fields");
        Field[] fields = c.getDeclaredFields(); // Look up fields.
        for (int i = 0; i < fields.length; i++)
            // Display them.
            print_field(fields[i]);

        System.out.println("  // Methods");
        Method[] methods = c.getDeclaredMethods(); // Look up methods.
        for (int i = 0; i < methods.length; i++)
            // Display them.
            print_method_or_constructor(methods[i]);

        System.out.println("}"); // End class member listing.
    }

    /** Return the name of an interface or primitive type, handling arrays. */
    public static String typename(Class t) {
        String brackets = "";
        while (t.isArray()) {
            brackets += "[]";
            t = t.getComponentType();
        }
        String name = t.getName();
        int pos = name.lastIndexOf('.');
        if (pos != -1)
            name = name.substring(pos + 1);
        return name + brackets;
    }

    /** Return a string version of modifiers, handling spaces nicely. */
    public static String modifiers(int m) {
        if (m == 0)
            return "";
        else
            return Modifier.toString(m) + " ";
    }

    /** Print the modifiers, type, and name of a field */
    public static void print_field(Field f) {
        System.out.println("  " + modifiers(f.getModifiers()) + typename(f.getType()) + " " + f.getName() + ";");
    }

    /**
     * Print the modifiers, return type, name, parameter types and exception type
     * of a method or constructor. Note the use of the Member interface to allow
     * this method to work with both Method and Constructor objects
     */
    public static void print_method_or_constructor(Member member) {
        Class returntype = null, parameters[], exceptions[];
        if (member instanceof Method) {
            Method m = (Method) member;
            returntype = m.getReturnType();
            parameters = m.getParameterTypes();
            exceptions = m.getExceptionTypes();
            System.out.print(
                    "  " + modifiers(member.getModifiers()) + typename(returntype) + " " + member.getName() + "(");
        } else {
            Constructor c = (Constructor) member;
            parameters = c.getParameterTypes();
            exceptions = c.getExceptionTypes();
            System.out.print("  " + modifiers(member.getModifiers()) + typename(c.getDeclaringClass()) + "(");
        }

        for (int i = 0; i < parameters.length; i++) {
            if (i > 0)
                System.out.print(", ");
            System.out.print(typename(parameters[i]));
        }
        System.out.print(")");
        if (exceptions.length > 0)
            System.out.print(" throws ");
        for (int i = 0; i < exceptions.length; i++) {
            if (i > 0)
                System.out.print(", ");
            System.out.print(typename(exceptions[i]));
        }
        System.out.println(";");
    }
}