Question

I need to compile an external java file (say a.java). This is the code i wrote for the same.

(String path contains the path to the java and class file)

    command[0] = "javac";
    command[1] = path+"a.java";
    p = Runtime.getRuntime().exec(command);        

The above code seems to work just fine. But the below code

    command[0] = "java";
    command[1] = "a";
    command[2] = "-cp";
    command[3] = "."+path+"a";
    p = Runtime.getRuntime().exec(command);        
    stdInput = new BufferedReader(new InputStreamReader(p.getInputStream()));
    stdError = new BufferedReader(new InputStreamReader(p.getErrorStream()));
    while ((temp = stdInput.readLine()) != null) result += "\n" + temp;
    while ((temp = stdError.readLine()) != null) result += "\n" + temp;

Causes the following error

java.lang.NoClassDefFoundError: a
Exception in thread "main" 

Could someone explaine the problem with this code. Thanks !

Answer 1

You’re specifying the class name first, and then the arguments for the classpath. The class name is always the last thing to come before the program-specific arguments. In your case, the classpath part will therefore not be treated as an option – it’ll be considered as two arguments (-cp and the path) to the Java program itself.

So instead of:

java a -cp (whatever)

you want

java -cp (whatever) a