Why does my converted string continue to append

Question

I'm currently trying to create a randomly generated string. Problem is, with the way I have it setup it continues to add on to itself.

My code ( I'm calling a lot of static variables from another class so don't worry about that portion)

    class Generate1 extends Thread{
    @Override
    public void run() {
        while(RUNNING == true){
                generate();
            try {
                Thread.sleep(1000);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
    }
    private void generate(){
        for(int i=0;i<length;i++){
            int decider = rando.nextInt(6)+1;

            if(decider == 1){
                sb1.append("A");
            }
            if(decider == 2){
                sb1.append("B");
            }
            if(decider == 3){
                sb1.append("C");
            }
            if(decider == 4){
                sb1.append("D");
            }
            if(decider == 5){
                sb1.append("E");
            }
            if(decider == 6){
                sb1.append("F");
            }
        }
        Log.d("PSS",sb1.toString()); // this here is the stringbuilder being outputted 
    }
}

if I set length to 2, in my log it would look something like:

DF DFCA DFCAEF

instead of my desired output:

DF CA EF

how do I fix this? ( I know this is probably a stupid question but it's late and pondering through code hurts my eyes and brain )

edit - shmosel brought light to what was wrong. It was a really simple fix to me overlooking something

Answer 1

You're using the same StringBuilder instance for each call to generate(). Use a fresh one instead:

private void generate(){
    StringBuilder sb1 = new StringBuilder(length);
    // ...
}