1	// Example 8.3 joi/examples/ReflectionDemo.java
     2	//
     3	//
     4	// Copyright 2003 Bill Campbell and Ethan Bolker
     5	
     6	import java.lang.reflect.*;
     7	
     8	// A short program to illustrate how Java uses
     9	// class information dynamically.
    10	//
    11	// This file declares class Greeting as well as class
    12	// ReflectionDemo. Java requires that a public class be
    13	// declared in a file that matches its name, but Greeting
    14	// is not marked public.
    15	//
    16	// %> java ReflectionDemo
    17	// Greeting@93dee9 is an instance of class Greeting
    18	// classOfG.toString(): class Greeting
    19	// classOfG.getName():  Greeting
    20	// fields in class Greeting (not inherited):
    21	// name: message, type: class java.lang.String
    22	// methods in class Greeting (not inherited):
    23	// invoking hello
    24	// hello, world!
    25	// Creating an object when you know the name of its class:
    26	// g = (Greeting)Class.forName("Greeting").newInstance();
    27	// g.toString(): Greeting@6f0472
    28	// Try to create an instance of nonexistent class Foo:
    29	// java.lang.ClassNotFoundException: Foo
    30	
    31	public class ReflectionDemo 
    32	{
    33	    public static void main( String[] args )  
    34	    {
    35	        Greeting g = new Greeting();
    36	        Class classOfG = g.getClass();
    37	        out(g.toString() + " is an instance of " +
    38	                           classOfG.toString());
    39	        out("classOfG.toString(): " + classOfG.toString());
    40	        out("classOfG.getName():  " + classOfG.getName());
    41	
    42	        out("fields in class Greeting (not inherited):");
    43	
    44	        Field[] greetingFields = classOfG.getFields();
    45	        for (int i=0; i < greetingFields.length; i++) {
    46	            Field f = greetingFields[i];
    47	            if (f.getDeclaringClass() == classOfG) {
    48	                out("name: " + f.getName() + ", type: " + f.getType());
    49	            }
    50	        }
    51	
    52	        out("methods in class Greeting (not inherited):");
    53	
    54	        Method[] greetingMethods = classOfG.getMethods();
    55	        for (int i=0; i < greetingMethods.length; i++) {
    56	            Method m = greetingMethods[i];
    57	            if (m.getDeclaringClass() == classOfG) {
    58	                out("invoking " + m.getName());
    59	                try {
    60	                    m.invoke(g, null);
    61	                }
    62	                catch( Exception e) {
    63	                    out(e.toString());
    64	                }
    65	            }
    66	        }
    67	
    68	        out("Creating an object when you know the name of its class:");
    69	        out("g = (Greeting)Class.forName(\"Greeting\").newInstance();");
    70	        try { 
    71	            g = (Greeting)Class.forName("Greeting").newInstance();
    72	            out( "g.toString(): " + g.toString());
    73	        }
    74	        catch (Exception e) { // couldn't find class
    75	            out(e.toString());
    76	        }
    77	
    78	        out("Try to create an instance of nonexistent class Foo:");
    79	        Object o;
    80	        try { 
    81	            o = Class.forName("Foo").newInstance();
    82	        }
    83	        catch (Exception e) { // couldn't find class
    84	            out(e.toString());
    85	        }
    86	    }
    87	
    88	    // too lazy to type "System.out.println()
    89	    public static void out( String s ) 
    90	    {
    91	        System.out.println(s);
    92	    }
    93	}
    94	 
    95	class Greeting 
    96	{ 
    97	    public String message = "hello, world";
    98	    
    99	    public void hello() 
   100	    {
   101	        System.out.println(message + "!");
   102	    }
   103	}