JavaCompilerobject giving an error WITHOUT ide

I am writing a program, where i need to compile one java file from within another, on the fly.

the code is correct, and is working correctly under BlueJ. but when i export a jar file, or run it from the command-line, it gives me a null-pointer exception!! PLS HELP!!!

Code :

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JavaCompiler compiler = ToolProvider.getSystemJavaCompiler();
           if(compiler.run(null, null, null, "Hello.java")
           {}
           else
           {}

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:-L

Quote:

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it gives me a null-pointer exception

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Its tough to give any advice given the code posted and a lack of any stack trace that references said code. Recommend you post an SSCCE which clearly demonstrates the problem.