How does bubbleSort know to start the loop over?

Question

Algorithms

public class Bubble {
  public static void main(String args[]){
    int bubble[] = {2,1,7,5,6,8,3,1};
    int temp;
    boolean check = false;
    while(check == false){
      check = true;
    
      for(int i = 0;i < bubble.length-1;i++){
        
        if(bubble[i] > bubble[i+1]){
          temp = bubble[i+1];
          bubble[i+1] = bubble[i];
          bubble[i] = temp;
          check = false;
        }
      }
    }
    for(int i = 0; i < bubble.length;i++){
      System.out.println(bubble[i]);
    }
  }
}

I understand every line, except for the place in the for condition.
Why does it say length -1? I don't quite understand how it works, but I think the answer lies in this.
The loop goes through all the indexes and then it should return and start again, but I don't see that in the code.

Answer 1

length-1 - because indexes start at zero, hence the last number is length-1.
"Start over" is the next iteration of the outer while loop. It will stop only when the condition in the if does not work inside the inner loop, i.e. when the array is sorted. Then check will become true and the next iteration of the while will not run.

Answer 2

Why does it say length -1

because indexing starts from 0, respectively the index of the last element is "size-1"
for( int i = 0; i < bubble.length-1;i++)