diff --git a/yuicompressor.php b/yuicompressor.php
index aef0d36..6da5652 100644
--- a/yuicompressor.php
+++ b/yuicompressor.php
@@ -2,104 +2,116 @@
 
 class YUICompressor
 {
-    
-    // absolute path to YUI jar file.
-    private static $JAR_PATH;
-    private static $TEMP_FILES_DIR;
-    private $options = array('type' => 'js',
-                             'linebreak' => false,
-                             'verbose' => false,
-                             'nomunge' => false,
-                             'semi' => false,
-                             'nooptimize' => false);
-    private $files = array();
-    private $string = '';
-    
-    // construct with a path to the YUI jar and a path to a place to put temporary files
-    function __construct($JAR_PATH, $TEMP_FILES_DIR, $options = array())
-    {
-        $this->JAR_PATH = $JAR_PATH;
-        $this->TEMP_FILES_DIR = $TEMP_FILES_DIR;
-        
-        foreach ($options as $option => $value)
-        {
-            $this->setOption($option, $value);
-        }
-    }
-    
-    // set one of the YUI compressor options
-    function setOption($option, $value)
-    {
-        $this->options[$option] = $value;
-    }
+	const DEFAULT_JAR_PATH = 'yuicompressor.jar';
+	const DEFAULT_TMP_DIR = '/tmp/yuicompressor';
+	
+	private $JAR_PATH;
+	private $TEMP_FILES_DIR;
+	private $options = [
+		'type'		 	=> 'js',
+		'linebreak' 	=> false,
+		'verbose'	 	=> false,
+		'nomunge'		=> false,
+		'semi'			=> false,
+		'nooptimize'	=> false
+	];
+	
+	private $files = array();
+	private $string = '';
 
-    // add a file (absolute path) to be compressed
-    function addFile($file)
-    {
-        array_push($this->files, $file);
-    }
-    
-    // add a strong to be compressed
-    function addString($string)
-    {
-        $this->string .= ' ' . $string;
-    }
+	public function __construct($JAR_PATH = null, $TEMP_FILES_DIR = null, $options = array())
+	{
+		$this->JAR_PATH = realpath ( $JAR_PATH ?: self::DEFAULT_JAR_PATH );
+		$this->TEMP_FILES_DIR = realpath ( $TEMP_FILES_DIR ?: self::DEFAULT_TMP_DIR );
+		
+		if ( ! file_exists ( $this->JAR_PATH) )
+			throw new Exception ( "Cannot find the JAR file: " . $this->JAR_PATH );
+		if ( ! file_exists ( $this->TEMP_FILES_DIR) )
+			throw new Exception ( "Cannot find the specified directory: " . $this->TEMP_FILES_DIR);	
+		
+		foreach ($options as $option => $value)
+			$this->setOption($option, $value);
+	}
     
-    // the meat and potatoes, executes the compression command in shell
-    function compress()
-    {
-        
-        // read the input
-        foreach ($this->files as $file) {
-    		$this->string .= file_get_contents($file) or die("Cannot read from uploaded file");        
-        }
-    	
-        // create single file from all input
-        $input_hash = sha1($this->string);
-        $file = $this->TEMP_FILES_DIR . '/' . $input_hash . '.txt';
-        $fh = fopen($file, 'w') or die("Can't create new file");
-        fwrite($fh, $this->string);
-        fclose($fh);
-    	
+	/**
+	 * Sets an option to the YUICompressor
+	 * @see http://yui.github.com/yuicompressor
+	 */
+	public function setOption ($option, $value)
+	{
+		$this->options[$option] = $value;
+	}
+
+	/**
+	 * Adds a file which should be compressed.
+	 * Path may be relative or absolute
+	 */
+	public function addFile ($file)
+	{
+		$file = realpath ($file);
+
+		if ( ! file_exists ($file))
+			throw new Exception ( "Cannot locate file: " . $file);
+		
+		array_push($this->files, $file);
+		$this->string .= file_get_contents ($file);
+	}
+
+	/**
+	 * Used to pass a string instead of a file,
+	 * i.e. with file_get_contents()
+	 */
+	public function addString ($string)
+	{
+		$this->string .= ' ' . $string;
+	}
+
+	/**
+	 * Compresses the given files and returns the compressed
+	 * data as a string.
+	 */
+	public function compress()
+	{
+		if ( strlen ( $this->string) == 0 )
+			throw new Exception ("Invalid State: Cannot compress when no data is given.");
+		
+		// create single file from all input
+		$input_hash = sha1($this->string);
+		$file = $this->TEMP_FILES_DIR . DIRECTORY_SEPARATOR . $input_hash . '.txt';
+		
+		$fh = fopen($file, 'w');
+		
+		if ( ! $fh )
+			throw new Exception ( "Cannot write data to temp file" );
+		
+		fwrite($fh, $this->string);
+		fclose($fh);
+
     	// start with basic command
-        $cmd = "java -Xmx32m -jar " . escapeshellarg($this->JAR_PATH) . ' ' . escapeshellarg($file) . " --charset UTF-8";
-    
-        // set the file type
-    	$cmd .= " --type " . (strtolower($this->options['type']) == "css" ? "css" : "js");
-    	
-    	// and add options as needed
-    	if ($this->options['linebreak'] && intval($this->options['linebreak']) > 0) {
-            $cmd .= ' --line-break ' . intval($this->options['linebreak']);
-    	}
+		$cmd = "java -Xmx32m -jar " . escapeshellarg($this->JAR_PATH) . ' ' . escapeshellarg($file) . " --charset UTF-8";
+		
+		// set the file type
+		$cmd .= " --type " . (strtolower($this->options['type']) == "css" ? "css" : "js");
+		
+		// and add options as needed
+		if ($this->options['linebreak'] && intval($this->options['linebreak']) > 0)
+			$cmd .= ' --line-break ' . intval($this->options['linebreak']);
 
-    	if ($this->options['verbose']) {
-    	   $cmd .= " -v";
-        }
-            
-		if ($this->options['nomunge']) {
+		if ($this->options['verbose'])
+			$cmd .= " -v";
+		
+		if ($this->options['nomunge'])
 			$cmd .= ' --nomunge';
-		}
 		
-		if ($this->options['semi']) {
+		if ($this->options['semi'])
 			$cmd .= ' --preserve-semi';
-		}
 		
-		if ($this->options['nooptimize']) {
+		if ($this->options['nooptimize'])
 			$cmd .= ' --disable-optimizations';
-		}
-    
-        // execute the command
-    	exec($cmd . ' 2>&1', $raw_output);
-    	
-    	// add line breaks to show errors in an intelligible manner
-        $flattened_output = implode("\n", $raw_output);
-    	
-    	// clean up (remove temp file)
-    	unlink($file);
-    	
-    	// return compressed output
-    	return $flattened_output;
-    }
+		
+		exec($cmd . ' 2>&1', $raw_output);
+		unlink($file);
+		
+		return $raw_output;
+	}
 }
-
-?>
\ No newline at end of file