How to generate random numbers and distribute them randomly to some buttons?

Question

I am rookie in android programming and want to generate some numbers randomly in a specific range. Provided that, the sum of two of them equals a certain number, I wrote the following in onCreate() and onRestart to re-generate them every time the activity starts, but it doesn't work every time:

//i1,i2,i3..... are initialized in the class body as integers

      do {
        i1=r.nextInt((30-1)+1)+1;
        i2=r.nextInt((30-1)+1)+1;
        i3=r.nextInt((30-1)+1)+1;
        i4=r.nextInt((30-1)+1)+1;
        i5=r.nextInt((30-1)+1)+1;
        i6=r.nextInt((30-1)+1)+1;
        i7=r.nextInt((30-1)+1)+1;
        i8=r.nextInt((30-1)+1)+1;
        i9=r.nextInt((30-1)+1)+1;
    }  while (i1+i2!=25);

    String[] str= {String.valueOf(i1),String.valueOf(i2),String.valueOf(i3),
            String.valueOf(i4),String.valueOf(i5),String.valueOf(i6),
            String.valueOf(i7),String.valueOf(i8),String.valueOf(i9)};

    btn1= (Button) findViewById(R.id.btn1);
    btn2= (Button) findViewById(R.id.btn2);
    btn3= (Button) findViewById(R.id.btn3);
    btn4= (Button) findViewById(R.id.btn4);
    btn5= (Button) findViewById(R.id.btn5);
    btn6= (Button) findViewById(R.id.btn6);
    btn7= (Button) findViewById(R.id.btn7);
    btn8= (Button) findViewById(R.id.btn8);
    btn9= (Button) findViewById(R.id.btn9);

    btn1.setOnClickListener(this);
    btn2.setOnClickListener(this);
    btn3.setOnClickListener(this);
    btn4.setOnClickListener(this);
    btn5.setOnClickListener(this);
    btn6.setOnClickListener(this);
    btn7.setOnClickListener(this);
    btn8.setOnClickListener(this);
    btn9.setOnClickListener(this);

    // this is the code which distribute the numbers randomly to the buttons:
    btn1.setText(str[random.nextInt(str.length)]);
    btn2.setText(str[random.nextInt(str.length)]);
    btn3.setText(str[random.nextInt(str.length)]);
    btn4.setText(str[random.nextInt(str.length)]);
    btn5.setText(str[random.nextInt(str.length)]);
    btn6.setText(str[random.nextInt(str.length)]);
    btn7.setText(str[random.nextInt(str.length)]);
    btn8.setText(str[random.nextInt(str.length)]);
    btn9.setText(str[random.nextInt(str.length)]);

Sometimes there are really two numbers of them whose sum is '25' but sometimes no, and I don't understand the reason. And, I want to know how to generate those numbers without repeating.

Answer 1

You can use Random class like this

  final int total=25;
  int otherno;
  Random num =new Random();
    int mo=num.nextInt(24);
  otherno= total-mo;

this will generate two no mo and otherno with sum equal 25 and it will be generated at a random if you want multiple pair just put this in for loop .I am using final key word as the total is not going to change for any no. for more info ,amout random no ex

Answer 2

In your activity.xml: take a linearLayout and id it as ll_main.

In your onCreate()

       ArrayList<Integer> al_list=new ArrayList<Integer>();
          //generate random number
         ll.removeAllViews();
          for(int i=0;i<10;i++)
              {

                  int num=getRandomNumberInRange(0,10);
                  if(num!=-1){
                 al_list.add(num); 
                 Button btn=new Button(this);
                 btn.setId(num);
                 btn.setText(num+"");
                 ll_main.addView(btn);                      
                  }


              }

    private  int getRandomNumberInRange(int min, int max) {

          if (min >= max) {
        throw new IllegalArgumentException("max must be greater than min");
    }

    Random r = new Random();
int num=r.nextInt((max - min) + 1) + min;
     if(al_list.contains(num))
       {
        getRandomNumberInRange(0,10);
     return -1;
        }
      else{
      return num;
      }  
}