java.lang.NullPointerException Error when compiling java application

[mickey0]

Hello,
I have my class file 'MyClass'; I would like compile it from my application; I wrote it but I got a java.lang.NullP ointerException
Any reasons for this?
thanks.

JavaCompiler compiler = ToolProvider.getSystemJavaCompiler();
	    		int res =  compiler.run(null, null, null, "MyClass.java" );           //here exception