The following example code shows how to make a method private in Ruby. source: Ruby Programming/Syntax/Classes [wikibooks.org]


Simple example:

 class Example
   def methodA
   end
   
   private # all methods that follow will be made private: not accessible for outside objects
   
   def methodP
   end
 end

If private is invoked without arguments, it sets access to private for all subseqent methods. It can also be invoked with named arguments.

Named private method example:

 class Example
   def methodA
   end
   
   def methodP
   end
   
   private :methodP
 end

Here private was invoked with an argument, altering the visibility of methodP to private.

This class uses reflection to enable you to invoke private methods on a class, or access its private fields. This can be useful for unit testing.

import java.lang.reflect.Field;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;

import junit.framework.Assert;

/**
 * Provides access to private members in classes.
 */
public class PrivateAccessor {
	
  public static Object getPrivateField (Object o, String fieldName) {   
	 // Check we have valid arguments... 
    Assert.assertNotNull(o);
    Assert.assertNotNull(fieldName);
    
    // Go and find the private field... 
    final Field fields[] = o.getClass().getDeclaredFields();
    for (int i = 0; i < fields.length; ++i) {
      if (fieldName.equals(fields[i].getName())) {
        try {
          fields[i].setAccessible(true);
          return fields[i].get(o);
        } 
        catch (IllegalAccessException ex) {
          Assert.fail ("IllegalAccessException accessing " + fieldName);
        }
      }
    }
    Assert.fail ("Field '" + fieldName +"' not found");
    return null;
  }
  
  public static Object invokePrivateMethod (Object o, String methodName, Object[] params) {   
		 // Check we have valid arguments... 
	    Assert.assertNotNull(o);
	    Assert.assertNotNull(methodName);
	    Assert.assertNotNull(params);
	    
	    // Go and find the private method... 
	    final Method methods[] = o.getClass().getDeclaredMethods();
	    for (int i = 0; i < methods.length; ++i) {
	      if (methodName.equals(methods[i].getName())) {
	        try {
	          methods[i].setAccessible(true);
	          return methods[i].invoke(o, params);
	        } 
	        catch (IllegalAccessException ex) {
	          Assert.fail ("IllegalAccessException accessing " + methodName);
	        }
	        catch (InvocationTargetException ite) {
	        	Assert.fail ("InvocationTargetException accessing " + methodName);	        	
	        }
	      }
	    }
	    Assert.fail ("Method '" + methodName +"' not found");
	    return null;
	  }  
}