How to generate random numbers from 1 to 8 without repeating them?

Question

I created the following shuffle puzzle using Java AWT. At the start of the program, as you can see, all numbers are in order. I want to generate random numbers without repeating. How to do this? Should I use the Random class?

import java.awt.*;
import java.awt.event.*;
class Puzzle extends Frame implements ActionListener
{
    Button b1,b2,b3,b4,b5,b6,b7,b8,b9;
    Puzzle()
    {
        setTitle("Shuffle");
        setSize(500,500);
        setLayout(new GridLayout(3,3));
        setVisible(true);
        Font f=new Font("Arial",Font.BOLD,100);

        b1=new Button("1");
                            b1.setFont(f);
                            b1.addActionListener(this);
        b2=new Button("2");
                            b2.setFont(f);
                            b2.addActionListener(this);
        b3=new Button("3");
                            b3.setFont(f);
                            b3.addActionListener(this);
        b4=new Button("4");
                            b4.setFont(f);
                            b4.addActionListener(this);
        b5=new Button("5");
                            b5.setFont(f);
                            b5.addActionListener(this);
        b6=new Button("6");
                            b6.setFont(f);
                            b6.addActionListener(this);
        b7=new Button("7");
                            b7.setFont(f);
                            b7.addActionListener(this);
        b8=new Button("8");
                            b8.setFont(f);
                            b8.addActionListener(this);
        b9=new Button(" ");
                            b9.setFont(f);
                            b9.addActionListener(this);

        add(b1); add(b2); add(b3);
        add(b4); add(b5); add(b6);
        add(b7); add(b8); add(b9);




    } 
    public void actionPerformed(ActionEvent ae)
    {
        if(ae.getSource() == b1)
        {
            if(b2.getLabel() == " ")
            {
                b2.setLabel(b1.getLabel());
                b1.setLabel(" ");
            }
        else if(b4.getLabel() == " ")
            {

              b4.setLabel(b1.getLabel());
                b1.setLabel(" ");
            }

        }
        if(ae.getSource() == b2)
        {
            if(b1.getLabel() == " ")
            {
                b1.setLabel(b2.getLabel());
                b2.setLabel(" ");
            }
        else if(b3.getLabel() == " ")
            {

              b3.setLabel(b2.getLabel());
                b2.setLabel(" ");
            }
            else if(b5.getLabel() == " ")
            {

              b5.setLabel(b2.getLabel());
                b2.setLabel(" ");
            }

        }
        if(ae.getSource() == b3)
        {
            if(b2.getLabel() == " ")
            {
                b2.setLabel(b3.getLabel());
                b3.setLabel(" ");
            }
        else if(b6.getLabel() == " ")
            {

              b6.setLabel(b3.getLabel());
                b3.setLabel(" ");
            }

        }
        if(ae.getSource() == b4)
        {
            if(b1.getLabel() == " ")
            {
                b1.setLabel(b4.getLabel());
                b4.setLabel(" ");
            }
        else if(b5.getLabel() == " ")
            {

              b5.setLabel(b4.getLabel());
                b4.setLabel(" ");
            }
            else if(b7.getLabel() == " ")
            {

              b7.setLabel(b4.getLabel());
                b4.setLabel(" ");
            }

        }
        if(ae.getSource() == b5)
        {
            if(b2.getLabel() == " ")
            {
                b2.setLabel(b5.getLabel());
                b5.setLabel(" ");
            }
        else if(b4.getLabel() == " ")
            {

              b4.setLabel(b5.getLabel());
                b5.setLabel(" ");
            }
            else if(b6.getLabel() == " ")
            {

              b6.setLabel(b5.getLabel());
                b5.setLabel(" ");
            }
            else if(b8.getLabel() == " ")
            {

              b8.setLabel(b5.getLabel());
                b5.setLabel(" ");
            }

        }
        if(ae.getSource() == b6)
        {
            if(b3.getLabel() == " ")
            {
                b3.setLabel(b6.getLabel());
                b6.setLabel(" ");
            }
        else if(b5.getLabel() == " ")
            {

              b5.setLabel(b6.getLabel());
                b6.setLabel(" ");
            }
        else if(b9.getLabel() == " ")
            {

              b9.setLabel(b6.getLabel());
                b6.setLabel(" ");
            }

        }
        if(ae.getSource() == b7)
        {
            if(b4.getLabel() == " ")
            {
                b4.setLabel(b7.getLabel());
                b7.setLabel(" ");
            }
        else if(b8.getLabel() == " ")
            {

              b8.setLabel(b7.getLabel());
                b7.setLabel(" ");
            }

        }
        if(ae.getSource() == b8)
        {
            if(b5.getLabel() == " ")
            {
                b5.setLabel(b8.getLabel());
                b8.setLabel(" ");
            }
        else if(b7.getLabel() == " ")
            {

              b7.setLabel(b8.getLabel());
                b8.setLabel(" ");
            }
            else if(b9.getLabel() == " ")
            {

              b9.setLabel(b8.getLabel());
                b8.setLabel(" ");
            }

        }
        if(ae.getSource() == b9)
        {
            if(b6.getLabel() == " ")
            {
                b6.setLabel(b9.getLabel());
                b9.setLabel(" ");
            }
        else if(b8.getLabel() == " ")
            {

              b8.setLabel(b9.getLabel());
                b9.setLabel(" ");
            }

        }

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

      new Puzzle();
    }
}

Maybe create an array from 1 - 8 and then shuffle it instead? java.util.Collections.shuffle(List>) — Daedric, Jul 11 '17 at 19:04
Have you made any attempt to shuffle? Please show that code. And yes, [Math.random()](https://docs.oracle.com/javase/7/docs/api/java/lang/Math.html#random()) is a good starting point. — Amber, Jul 11 '17 at 19:05
In the place of b1=new Button("1"),I did the following: [code] Random rand=new Random(); int a=rand.nextInt(); b1=new Button(+a); but it repeats the numbers. [\code] — , Jul 11 '17 at 19:08

Yahya · Accepted Answer · 2017-07-11T19:30:25.817

1

You can do something like this:

// global scope
List<Integer> container = new ArrayList<>();

//populate it
for(int i =1; i<=8; i++){
   container.add(i);
}
..........
..........
..........
public static int getRandom(){
    //to refill it if ya need to call it more than 8 times
    //if(container.size()==0){for(int i=1; i<=8; i++){container.add(i);} 
    Random generator = new Random();

    Integer randomNumber = container.get(generator.nextInt(container.size()));

    container.remove(randomNumber);

    return randomNumber;
}

Furthermore, if you want to name/label every button with a unique number from 1 to 8 randomly, simply you do for example:

b1=new Button(String.valueOf(getRandom()));

And so on.

edited Jul 11 '17 at 19:30

answered Jul 11 '17 at 19:07

Yahya

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Thanks,but it does repeat the same number sometimes right? – Jul 11 '17 at 19:15
@VishnuVardhan Not at all , it never repeats the number after returning it. every time you call the method it returns a unique number. But if you want to invoke the method more than 8 times , it will in case you refill it... I can add a little modification though – Yahya Jul 11 '17 at 19:17
I have implemented what you said. But how should I add the randomly generated numbers to my button? – Jul 11 '17 at 19:25
@VishnuVardhan Do ya want to name/label every button with a number from 1 to 8? – Yahya Jul 11 '17 at 19:27
yes. Because the buttons show the randomly generated numbers and the user have to arrange them in ascending order to win the game. – Jul 11 '17 at 19:30

El8dN8 · Answer 2 · 2017-07-11T20:19:15.303

A general answer:

EDIT: I apologize, here's essentially the same thing the other guy posted. He got to it first.

ArrayList<Integer> draw = new ArrayList<Integer>();
for(int i = 1; i<=8; i++){
    draw.add(i); //Add every number once
}

//Every time you call it, you pick a random item from the list.
//Then you remove it from it to prevent being recalled. Therefore it won't be re-accesed.
Random r = new Random();
int placeholder = r.nextInt(draw.size());
int num = draw.get(placeholder);
draw.remove(placeholder);

For you, this is what you should do:

...
ArrayList<Button> buttonlist = new ArrayList<Button>(); /// ADD THIS. Put this outside the method/function.
...
Puzzle(){
    setTitle("Shuffle");
    setSize(500,500);
    setLayout(new GridLayout(3,3));
    setVisible(true);
    Font f=new Font("Arial",Font.BOLD,100);

    b1=new Button("1");
                        b1.setFont(f);
                        b1.addActionListener(this);
                        buttonlist.add(b1); /// ADD THIS
    b2=new Button("2");
                        b2.setFont(f);
                        b2.addActionListener(this);
                        buttonlist.add(b2); /// ADD THIS
    b3=new Button("3");
                        b3.setFont(f);
                        b3.addActionListener(this);
                        buttonlist.add(b3); /// ADD THIS
    b4=new Button("4");
                        b4.setFont(f);
                        b4.addActionListener(this);
                        buttonlist.add(b4); /// ADD THIS
    b5=new Button("5");
                        b5.setFont(f);
                        b5.addActionListener(this);
                        buttonlist.add(b5); /// ADD THIS
    b6=new Button("6");
                        b6.setFont(f);
                        b6.addActionListener(this);
                        buttonlist.add(b6); /// ADD THIS
    b7=new Button("7");
                        b7.setFont(f);
                        b7.addActionListener(this);
                        buttonlist.add(b7); /// ADD THIS
    b8=new Button("8");
                        b8.setFont(f);
                        b8.addActionListener(this);
                        buttonlist.add(b8); /// ADD THIS
    b9=new Button(" ");
                        b9.setFont(f);
                        b9.addActionListener(this);
                        buttonlist.add(b9); /// ADD THIS
    Random r = new Random(); /// ADD THIS
    while(buttonlist.size() != 0){ /// ADD THIS
        int placeholder = r.nextInt(buttonlist.size()); /// ADD THIS
        Button button = buttonlist.get(placeholder); /// ADD THIS
        add(button); /// ADD THIS AFTER REPLACING all the original add(b1)...
        buttonlist.remove(placeholder); /// ADD THIS
    } /// ADD THIS
}

This is a little bit different from the other's response who recommended givingg it an individual name, I believe this method would work a little better so b1 doesn't have the label 3 or something. This way the answer to the shuffle the order would just be in b1,b2,b3... instead of a random order. This retains order while actually shuffling the buttons on the border, otherwise you will have difficulty identifying the objects.

Thanks a lot.But how should I place it in the button? And the above method repeats the same number sometimes right? — , Jul 11 '17 at 19:17
It does not. As it removes it from the list with draw.remove(placeholder); — El8dN8, Jul 11 '17 at 19:18
@VishnuVardhanSIstla, Did this work? or did you something else? — El8dN8, Jul 11 '17 at 19:49
@VishnuVardhanSIstla Sorry, I copied and pasted. that "draw" should be "buttonlist." The issue will be fixed in a couple seconds. — El8dN8, Jul 11 '17 at 20:02
@user277827 nope. Not working. I compiled it and a awt window appeared looking empty. Not even the old buttons which I created were visible. — , Jul 11 '17 at 20:11
@VishnuVardhanSIstla, If you copied and pasted It may cause an issue. Rollback to a working set where you got the 9 buttons, and add the lines that I will //////////Comment. Remember to replace the add(b1).... with the code below. — El8dN8, Jul 11 '17 at 20:17

Edwin Buck · Answer 3 · 2017-07-11T19:21:51.780

Since you are randomly selecting a number from a collection, don't use the Random number generator to pick the number, use the Random number generator to pick from the remaining available numbers.

 List<Integer> choices = getNewChoices();
 int choice = choices.remove(random.nextInt(choices.size());

Choices will eventually get smaller and smaller, but the unselected elements are still in the List.

You can wrap that into a protective method selectOne

public class Whatever {

     public void run() {
         ...
         List<Integer> choices = getNewChoices();
         ...
         int choice = selectOne(choices);
     }

     public List<Integer> getNewChoices() {
         return Arrays.toList(new Integer[] { 1, 2, 3, 4, 5, 6, 7, 8});
     }

     public int selectOne(List<Integer> choices) {
         if (choices.length() > 0) {
             return choices.remove(random.nextInt(choices.size());
         }
         throw new RuntimeException("out of choices");
     }
 }

How to generate random numbers from 1 to 8 without repeating them?

3 Answers3