Is it possible to shutdown computer from java code?
<p>In a beginners programming class we were assigned to store classmarks, average, lowest mark, highestmark etc. </p>

<p>We were also asked to shutdown the computer. </p>

<p>I outputted a menu and one of the cases was to shut down the computer. </p>

<p>However it isn't working. Method 4 and method 8 are the only ones associated with the problem.</p>

<pre><code>import javax.swing.*;
import java.io.*;

class ClassMarks {

    String names[];
    int marks[];
    int counter;
    String marksString;

    final String PASSWORD = "Top Secret";
    String name, surname;
    int mark;

    int total;
    double average;

    //method to check password
    public void checkPassword() {
        int counter = 0;
        String password_user;
        do {
            password_user = JOptionPane.showInputDialog("Enter password: ");

            if (password_user.equals(PASSWORD)) {

                JOptionPane.showMessageDialog(null, "Access Granted");
                outputMenu();
            } else {
                JOptionPane.showMessageDialog(null, "Access Denied");
            }
            counter++;
        } while ((counter &lt; 4) &amp;&amp; !(password_user.equals(PASSWORD)));
        JOptionPane.showMessageDialog(null, "No more attempts available");

    }

    public void compulsoryMethod() {

        String namesString = JOptionPane.showInputDialog("Enter number of students");
        int noOfNames = Integer.parseInt(namesString);

        //print all the array elements
        for (counter = 0; counter &lt; noOfNames; counter++) {
            names[counter] = JOptionPane.showInputDialog("Enter names");
            marksString = JOptionPane.showInputDialog("Enter Mark for" + names[counter] + " ");
            marks[counter] = Integer.parseInt(marksString);
        }
    }

    // method 4
    public void outputMenu() {
        int input;
        do {

            String stringInput = JOptionPane.showInputDialog("Choose the decision you want to make: \n\n 1.Enter marks \n 2. See marks \n 3.Find Average \n 4.See highest mark \n 5.See lowest mark \n 6.See any mark above average \n 7.Turn off this Pc/Laptop/any other device\n 8.See Grade");

            input = Integer.parseInt(stringInput); // to convert stringInput which is String to input which is int

            switch (input) {
                case 1:
                    enterMarks();
                    break;
                case 2:
                    viewMarks();
                    break;
                case 3:
                    averageMark();
                    break;
                case 4:
                    highestMark();
                    break;
                case 5:
                    lowestMark();
                    break;
                case 6:
                    markAboveAverage();
                    break;
                case 7:
                    shutDown();
                    break;
                case 8:
                    viewMarks();
                    break;

                default:
                    JOptionPane.showMessageDialog(null, "Invalid choice");
            }
        } while (input != 7);
    }

    //method 3
    public void enterMarks() {

        String namesString = JOptionPane.showInputDialog("Enter no of students:");
        int noOfNames = Integer.parseInt(namesString);

        names = new String[noOfNames];
        marks = new int[noOfNames];
        for (counter = 0; counter &lt; marks.length; counter++) {
            names[counter] = JOptionPane.showInputDialog("Enter names:");

            marksString = JOptionPane.showInputDialog("Enter Mark for " + names[counter] + " ");
            marks[counter] = Integer.parseInt(marksString);

        }

    }

    // method 5
    public void viewMarks() {

        for (counter = 0; counter &lt; marks.length; counter++) {
            JOptionPane.showMessageDialog(null, new JTextArea(names[counter] + "\t\t" + marks[counter] + "\t\t" + displayGrade(marks[counter])));
        }
    }

    //method 6
    public void averageMark() {
        int total = 0;
        for (counter = 0; counter &lt; marks.length; counter++) {
            total = total + marks[counter];
        }

        average = total / 5;
        JOptionPane.showMessageDialog(null, "Average is:" + average);
    }

    //method 7
    public void highestMark() {
        int large = 0;
        int num;

        // i starts from 2 because we already took one num value
        for (int counter = 0; counter &lt; marks.length; counter++) {

            if (marks[counter] &gt; large) {
                large = marks[counter];
            }
        }
        JOptionPane.showMessageDialog(null, large);
    }

    //method 8
    public void lowestMark() {

        int small = 100;
        int num;

        for (int counter = 0; counter &lt; marks.length; counter++) {

            if (marks[counter] &lt; small) {
                small = marks[counter];
            }

        }
        JOptionPane.showMessageDialog(null, small);

    }

    //method 9
    public void markAboveAverage() {

        averageMark();

        for (int counter = 0; counter &lt; marks.length; counter++) {

            if (marks[counter] &gt; average) {

                JOptionPane.showMessageDialog(null, marks[counter] + ": This mark is above average");
            } else {
                JOptionPane.showMessageDialog(null, marks[counter] + "This mark is below average");
            }
        }
    }

    //method 10
    public void (main String[]) throws IOException {
        Runtime runtime = Runtime.getRuntime();
        Process proc = runtime.exec("shutdown -s -t 0");
        System.exit(0);
    }

    //method11
    public char displayGrade(int marks) {

        char grade = ' ';
        if ((marks &gt;= 0) &amp;&amp; (marks &lt;= 20)) {
            grade = 'U';

        }
        if ((marks &gt;= 21) &amp;&amp; (marks &lt;= 40)) {
            grade = 'E';

        }

        if ((marks &gt;= 41) &amp;&amp; (marks &lt;= 60)) {
            grade = 'D';

        }

        if ((marks &gt;= 61) &amp;&amp; (marks &lt;= 80)) {
            grade = 'C';

        }

        if ((marks &gt;= 81) &amp;&amp; (marks &lt;= 90)) {
            grade = 'B';

        }

        if ((marks &gt;= 91) &amp;&amp; (marks &lt;= 100)) {
            grade = 'A';

        }

        return grade;
    }    
}
</code></pre>