Java error “Value of local variable is not used”

Question

I am really new to java (started learning 2 days ago). Sorry if this is a stupid question. I am trying to learn how to use rt.exec & similar methods so I tried to make a

Answer 1

There is no such thing as a stupid qiestion(only misplaced ones, in the worst case).

The "Editor does not contain a main type" refers to the fact that you have not defined a main method. All java programs require a main method, as such:

public static void main(String [] args){
    
}

This is where you must place your code.

The "Value not used" is just a warning; it tells you that your variable p only exists within the try-block. You can declare your p-variable before the try - that way, you can use it outside the try-scope(the scope of a variable refers to where it exists, in this case, only inside the try-block).

If you want to use your p, this is what you're after:

public class Main {
    public static void main(String[] args) {
        Process p;
        try {
            Runtime rt = Runtime.getRuntime();
            p = rt.exec("calc.exe");
        } catch(Exception exc) {/*handle exception*/}
    }
}

[EDIT]: Note that it is part of the java coding convention to use Capital letters for the first letter of a class, e.g. Main.java(not main.java)