Is it possible to shutdown computer from java code?

Question

In a beginners programming class we were assigned to store classmarks, average, lowest mark, highestmark etc.

We were also asked to shutdown the computer.

I outputted a menu and one of the cases was to shut down the computer.

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

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 < 4) && !(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 < 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 < 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 < 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 < 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 < marks.length; counter++) {

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

    //method 8
    public void lowestMark() {

        int small = 100;
        int num;

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

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

        }
        JOptionPane.showMessageDialog(null, small);

    }

    //method 9
    public void markAboveAverage() {

        averageMark();

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

            if (marks[counter] > 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 >= 0) && (marks <= 20)) {
            grade = 'U';

        }
        if ((marks >= 21) && (marks <= 40)) {
            grade = 'E';

        }

        if ((marks >= 41) && (marks <= 60)) {
            grade = 'D';

        }

        if ((marks >= 61) && (marks <= 80)) {
            grade = 'C';

        }

        if ((marks >= 81) && (marks <= 90)) {
            grade = 'B';

        }

        if ((marks >= 91) && (marks <= 100)) {
            grade = 'A';

        }

        return grade;
    }    
}

We need a lot less code and a lot more background information. What happens when you try to run your shutdown code? Does it give you a specific error message? Does it do nothing and quit? Does it cause a freeze? Does it make your computer play Joy to the World? What operating system are you running? Mac (version?) Linux (what kind, what version?) — Robert Columbia
– Robert Columbia, Commented Dec 23, 2016 at 14:29
Robert Columbia - You should always keep in mind that i am a beginner so go easy on me :). I am running this program on windows and this error is popping up error: <identifier> expected --->public void (main String[]) throws IOException{ — Nicholas Borg
– Nicholas Borg, Commented Dec 24, 2016 at 10:15
Robert, the program does work without the shutdown choice so the problem is from the shut down — Nicholas Borg
– Nicholas Borg, Commented Dec 24, 2016 at 10:23

Community · Accepted Answer · 2020-06-20 09:12:55Z

4

You can use CMD command to shut or restart your computer like

shutdown -s -t 10

Here is a way to shut and restart your computer that using windows :

Shut down your computer:

public void shutdownPC(int time){
    try {
        Runtime r = Runtime.getRuntime();
        // Shutdown system time mean, time to wait before my system will shutdow or restart
        r.exec("shutdown -s -t " + time);
    } catch (NumberFormatException | IOException e) {
        JOptionPane.showMessageDialog(null, "Restart failed.");
    }
}

Restart your computer:

public void restartPC(int time){
    try {
        Runtime r = Runtime.getRuntime();
        // Restart system
        r.exec("shutdown -r -t " + time);
    } catch (NumberFormatException | IOException e) {
        JOptionPane.showMessageDialog(null, "Restart failed.");
    }
}

If you are using linux or mac you can use this two command :

sudo poweroff

and

sudo reboot

You can learn about command line linux and mac

EDIT

First

You get and error in the 4th method in the case 7 because you call shutDown();, and this not exist in your code, so you should to call the right method.

Second

You get an error in the main method public void (main String[]) throws IOException {, because it is not created correctly, so you need to create it like this:

public static void main(String[] args) throws IOException {
   //your code here
}

don't forgot to import this import java.io.IOException;

Third

And about the two method that i set them in the previous answer, you need to make them static:

public static void shutdownPC(int time) {}

public static void restartPC(int time) {}

Fourth

And to call them from your method 4, you need to specify the time to restart or to shutdown you pc like this:

case 7:
    shutdownPC(5);//5 mean 5 second if you want to shut the pc imidattilly just set it 0
    break;

Hope this can help you.

edited Jun 20, 2020 at 9:12

CommunityBot

11 silver badge

answered Dec 23, 2016 at 14:35

Youcef LAIDANI

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6 Comments

Nicholas Borg Over a year ago

So i tried the first example but then an error popped up in the menu at method 2 saying cannot find symbol ...MIND YOU I ARRANGED THE OBJECT TO SHUTDOWNPC so the error isn't actually about the object name.

Youcef LAIDANI Over a year ago

what did you mean @NicholasBorg ? what error you get in my solution or what?

Nicholas Borg Over a year ago

I arranged the previous error now what appeared was error: method shutdownPC in class ClassMarks cannot be applied to given types;

Youcef LAIDANI Over a year ago

ok i will create another answer, this will help you @NicholasBorg

Youcef LAIDANI Over a year ago

i already create another answer you can check it @NicholasBorg

|

Keval Pithva · Accepted Answer · 2016-12-27 11:32:52Z

0

I would like to add some MrLy code to make programme very intelligent

public static void shutdownPC(int time){
    try {
        Runtime r = Runtime.getRuntime();
        // Shutdown system time mean, time to wait before my system will shutdow or restart
        if(System.getProperty("sun.desktop").equalsIgnoreCase("windows"))
        {
            r.exec("shutdown -s -t " + time);
        }
        else
        {
            r.exec("sudo poweroff");
        }  
    } catch (NumberFormatException | IOException e) {
        JOptionPane.showMessageDialog(null, "Restart failed.");
    }
}

edited Dec 27, 2016 at 11:32

answered Dec 23, 2016 at 15:48

Keval Pithva

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1 Comment

Nicholas Borg Over a year ago

error: method shutdownPC in class ClassMarks cannot be applied to given types;

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