PHP validation class using method dispatch

I wrote this validation class. I'm kinda new to the whole OO(PHP) style, so I don't know if my class is acceptable. I looked around at other people's validation classes, but most are huge (1k+ lines of code) or similar to mine in some ways.

class Validation{

    private $errors = array();
    private $defaultErrors = array();

    public function __construct(){
        $this->defaultErrors = array(
            'required' => "This field is required",
            'unique' => "This value is already in use",
            'number' => "Not a number",
            'numberRange' => "Number is not in range",
            'email' => "Not a valid email",
            'characters' => "Only letters are allowed",
            'length' => "This value is too long or short",
            'postcode' => "This postcode is not valid",
            'message' => "This message is not valid",
            'compareString' => "These values are not the same"
        );
    }

    public function validationMethod($data) {
        foreach ($data as $input => $rule) {
            $methods = explode('|', $rule[0]);
            foreach ($methods as $method) {
                switch ($method) {
                    case 'number':
                        self::validate($method, 'validateNumber', $input, null);
                        break;
                    case 'numberRange':
                        self::validate($method, 'numberRange', $input, array($rule[1], $rule[2]));
                        break;
                    case 'characters':
                        self::validate($method, 'validateChars', $input, null);
                        break;
                    case 'length':
                        self::validate($method, 'validateLength', $input, array($rule[1], $rule[2]));
                        break;
                    case 'email':
                        self::validate($method, 'validateEmail', $input, null);
                        break;
                    case 'postcode':
                        self::validate($method, 'validatePostcode', $input, null);
                        break;
                    case 'message':
                        self::validate($method, 'validateMessage', $input, null);
                        break;
                    case 'compareString':
                        self::validate($method, 'compareStrings', $input, $rule[1]);
                        break;
                    default:                            
                        break;
                }
            }
        }

        if(count($this->errors) > 0): return false; endif;
        return true;
    }

    private function validate($method, $func, $input, $options) {
        $tmp = self::$func($input, $options);
        if(!$tmp): self::setErrors($method); endif;
    }

    private function setErrors($method) {
        $this->errors[] = $this->defaultErrors[$method];
    }

    public function getErrors() {
        return $this->errors;
    }

    private function validateNumber($data) {
        if(is_int($data)):return true; endif;
        return false;
    }

    private function numberRange($number, $range) {
        if(($number > $range[0]) && ($number < $range[1])): return true; endif;
        return false;
    }

    private function validateChars($data) {
        if (ctype_alpha(str_replace(' ', '', $data)) === true): return true; endif;
        return false;
    }

    private function validateLength($data, $limit) {
        $data = strlen($data);
        if(($data > $limit[0]) && ($data < $limit[1])): return true; endif;
        return false;
    }

    private function validateEmail($data) {
        if(preg_match("~^[a-z0-9!#$%&'*+/=?^_`{|}-]+(?:\.[a-z0-9!#$%&'*+/=?^_`{|}-]+)*@(?:[a-z0-9](?:[a-z0-9-]*[a-z0-9])?\.)+[a-z0-9](?:[a-z0-9-]*[a-z0-9])?$~", $data)):return true; endif;
        return false;
    }

    private function validatePostcode($data) {
        if(preg_match('/^([0-9]{4}[a-zA-Z]{2})$/', $data)): return true; endif;
        return false;
    }

    private function validateMessage($data) {
        if($data == strip_tags($data)): return true; endif;
        return false;
    }

    private function compareStrings($string1, $string2) {
        if($string1 === $string2): return true; endif;
        return false;
    }
}

Anyway, Any suggestions on how to improve this class? All suggestions are greatly appreciated :)