Use of Comparator custom sorting

Java's custom sorting methods for collections are:

Arrays.sort(T[],Comparator<? super T> c);
Collections.sort(List<T> list,Comparator<? super T> c);

Record the pair here Comparator's own understanding.

Demo code is as follows:

1. Entity class code:
class SortObj {

        String letter;
        int num;

        public SortObj(String letter, int num) {
            this.letter = letter;
            this.num = num;
        }

    }


2. Comparator implementation code, The two classes are:
/**
     * Character sorting (# comes last)
     */
    class StrComparator implements Comparator<SortObj> {

        @Override
        public int compare(SortObj o1, SortObj o2) {
            if("#".equals(o1.letter) && "#".equals(o2.letter)){
                return 0;
            }else if("#".equals(o1.letter)){
                return 1;
            }else if("#".equals(o2.letter)){
                return -1;
            }
            return o1.letter.compareTo(o2.letter);

        }
    }

    /**
     * 数字排序 （升序）
     */
    class NumComparator implements Comparator<SortObj> {

        @Override
        public int compare(SortObj o1, SortObj o2) {

            if(o1.num > o2.num){
                return 1;
            }else if(o1.num < o2.on one){
                return -1;
            }else{
                return 0;
            }
        }
    }

3.调用排序并展示：
findViewById(R.id.btn_num_sort).setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Collections.sort(dataNum, new NumComparator());
                printInfo(dataNum);
            }
        });

        findViewById(R.id.btn_str_sort).setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Collections.sort(dataStr, new StrComparator());
                printInfo(dataStr);
            }
        });

display the result as follows:
Number sorting:
SortTest: (b,1) (r,2) (a,2) (a,3) (#,4) (#,5)
Character sorting :
SortTest: (a,3) (a,2) (b,1) (r,2) (#,4) (#,5)


The sorting algorithm is executed in the compare: the
returned results are 3 kinds: positive integer (1 ), negative integer (-1), 0

's own understanding of the returned result ( purely my own opinion ):
This is a bit of a bubble sort. When it is a positive integer, swap the positions of o1 and o2, when it is a negative integer. , do not change positions