netbeans中的JavaScript错误“ java.lang.NullPointerException”

Question

Im trying to use javascript with netbeans. Im supposed to make a mastermind game using javascript. when ı tried to add something to .js ı always have this error;

Exception in thread "main" java.lang.NullPointerException
at java.io.Reader.<init>(Reader.java:78)
at java.io.InputStreamReader.<init>(InputStreamReader.java:72)
at assgn1.Main.main(Main.java:32)

ı couldnt figur out why. thanks for any help.

my codes are;

Main.java

package assgn1;

import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.Reader;
import javax.script.ScriptEngine;
import javax.script.ScriptEngineManager;
import javax.script.ScriptException;


public class Main {


public static void main(String[] args) throws ScriptException {
    // TODO code application logic here
    // create manager
    ScriptEngineManager m = new ScriptEngineManager();
    // create javascript script engine
    ScriptEngine js = m.getEngineByName("javascript");
    // evaluate "hello.js"
    InputStream strm = Main.class.getResourceAsStream("/hello.js");
    Reader r = new InputStreamReader(strm);
    js.eval(r);
}

}

hello.js

importPackage(javax.swing);
importClass(java.lang.System);

function exit(){
   System.exit(0);
}
var f= new JFrame("MasterMind");
var b= new JButton("exit");
b.addActionListener(exit);

f.add(path);
f.add(b,"South");
f.setSize(800,800);
f.visible=true;

Answer 1

You should check if

InputStream strm = Main.class.getResourceAsStream("/hello.js");

doesnt return a null object because the path is wrong. Seems like you get the NullPointerException because of that.