showclass.java

These are the examples from the book Java Examples in a Nutshell, 2nd Edition, by David Flanagan.

/*
 * Copyright (c) 2000 David Flanagan.  All rights reserved.
 * This code is from the book Java Examples in a Nutshell, 2nd 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.
 * You may distribute it non-commercially as long as you retain this notice.
 * For a commercial use license, or to purchase the book (recommended),
 * visit http://www.davidflanagan.com/javaexamples2.
 */
package com.davidflanagan.examples.reflect;
import java.lang.reflect.*;

/** 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(";");
    }
}