class getMethod Reflection

Method method = A.class.getMethod("ff", new Class<?>[]{});

Method method = A.class.getMethod("ff", null);

Method method = A.class.getMethod("ff", (Class<?>)null);

    /**
     * Returns a <code>Method</code> object that reflects the specified public
     * member method of the class or interface represented by this
     * <code>Class</code> object. The <code>name</code> parameter is a
     * <code>String</code> specifying the simple name of the desired method. The
     * <code>parameterTypes</code> parameter is an array of <code>Class</code>
     * objects that identify the method's formal parameter types, in declared
     * order. If <code>parameterTypes</code> is <code>null</code>, it is 
     * treated as if it were an empty array.
     *
     * <p> If the <code>name</code> is "{@code <init>};"or "{@code <clinit>}" a
     * <code>NoSuchMethodException</code> is raised. Otherwise, the method to
     * be reflected is determined by the algorithm that follows.  Let C be the
     * class represented by this object:
     * <OL>
     * <LI> C is searched for any <I>matching methods</I>. If no matching
     *         method is found, the algorithm of step 1 is invoked recursively on
     *         the superclass of C.</LI>
     * <LI> If no method was found in step 1 above, the superinterfaces of C
     *      are searched for a matching method. If any such method is found, it
     *      is reflected.</LI>
     * </OL>
     *
     * To find a matching method in a class C:&nbsp; If C declares exactly one
     * public method with the specified name and exactly the same formal
     * parameter types, that is the method reflected. If more than one such
     * method is found in C, and one of these methods has a return type that is
     * more specific than any of the others, that method is reflected;
     * otherwise one of the methods is chosen arbitrarily.
     *
     * <p>Note that there may be more than one matching method in a
     * class because while the Java language forbids a class to
     * declare multiple methods with the same signature but different
     * return types, the Java virtual machine does not.  This
     * increased flexibility in the virtual machine can be used to
     * implement various language features.  For example, covariant
     * returns can be implemented with {@linkplain
     * java.lang.reflect.Method#isBridge bridge methods}; the bridge
     * method and the method being overridden would have the same
     * signature but different return types.
     *
     * <p> See <em>The Java Language Specification</em>, sections 8.2 and 8.4.
     *
     * @param name the name of the method
     * @param parameterTypes the list of parameters
     * @return the <code>Method</code> object that matches the specified
     * <code>name</code> and <code>parameterTypes</code>
     * @exception NoSuchMethodException if a matching method is not found
     *            or if the name is "&lt;init&gt;"or "&lt;clinit&gt;".
     * @exception NullPointerException if <code>name</code> is <code>null</code>
     * @exception  SecurityException
     *             If a security manager, <i>s</i>, is present and any of the
     *             following conditions is met:
     *
     *             <ul>
     *
     *             <li> invocation of 
     *             <tt>{@link SecurityManager#checkMemberAccess
     *             s.checkMemberAccess(this, Member.PUBLIC)}</tt> denies
     *             access to the method
     *
     *             <li> the caller's class loader is not the same as or an
     *             ancestor of the class loader for the current class and
     *             invocation of <tt>{@link SecurityManager#checkPackageAccess
     *             s.checkPackageAccess()}</tt> denies access to the package
     *             of this class
     *
     *             </ul>
     *
     * @since JDK1.1
     */
    public Method getMethod(String name, Class<?>... parameterTypes)
        throws NoSuchMethodException, SecurityException {
    // be very careful not to change the stack depth of this
    // checkMemberAccess call for security reasons 
    // see java.lang.SecurityManager.checkMemberAccess
        checkMemberAccess(Member.PUBLIC, ClassLoader.getCallerClassLoader(), true);
        Method method = getMethod0(name, parameterTypes);
        if (method == null) {
            throw new NoSuchMethodException(getName() + "." + name + argumentTypesToString(parameterTypes));
        }
        return method;
    }