Comparator

Comparator

    public static void main(String[] args) {

        List integerList = Arrays.asList(5, 2, 6, 5, 8, 8, 4);
        Comparator comparator = new Comparator() {
            @Override
            public int compare(Integer o1, Integer o2) {
                // 升序
                // 此处的 o1 对应数组 a[1] ; o2 对应数组 a[0]
                // 如果 o1 > o2 即 a[1] > a[0] 依次递增，升序
                if(o1 > o2){
                    return 1 ;
                }else if(o1 < o2){
                    // 如果 o1 < o2 反转
                    return -1 ;
                }
                return 0;
            }
        };
        Collections.sort(integerList,comparator);
        // [2, 4, 5, 5, 6, 8, 8]
        System.out.println(integerList);


        Comparator comparatorAsc = new Comparator() {
            @Override
            public int compare(Integer o1, Integer o2) {
                return o1 - o2;
            }
        };

        List integerList1 = Arrays.asList(1, 2, 3, 4, 5, 6, 7, 8);
        // [1, 2, 3, 4, 5, 6, 7, 8]
        System.out.println(integerList1);
        Collections.sort(integerList1,comparatorAsc);
        // [1, 2, 3, 4, 5, 6, 7, 8]
        System.out.println(integerList1);

        List integerList2 = Arrays.asList(8, 7, 6, 5, 4, 3, 2, 1);
        // [8, 7, 6, 5, 4, 3, 2, 1]
        System.out.println(integerList2);
        Collections.sort(integerList2,comparatorAsc);
        // [1, 2, 3, 4, 5, 6, 7, 8]
        System.out.println(integerList2);

        Comparator comparatorDesc = new Comparator() {
            @Override
            public int compare(Integer o1, Integer o2) {
                return o2 - o1;
            }
        };
        List integerList3 = Arrays.asList(1, 2, 3, 4, 5, 6, 7, 8);
        // [1, 2, 3, 4, 5, 6, 7, 8]
        System.out.println(integerList3);
        Collections.sort(integerList3,comparatorDesc);
        // [1, 2, 3, 4, 5, 6, 7, 8]
        System.out.println(integerList3);

        List integerList4 = Arrays.asList(8, 7, 6, 5, 4, 3, 2, 1);
        // [8, 7, 6, 5, 4, 3, 2, 1]
        System.out.println(integerList4);
        Collections.sort(integerList4,comparatorDesc);
        // [1, 2, 3, 4, 5, 6, 7, 8]
        System.out.println(integerList4);
        }

	// Collections - sort 

    public static  void sort(List list, Comparator c) {
        Object[] a = list.toArray();
        Arrays.sort(a, (Comparator)c);
        ListIterator i = list.listIterator();
        for (int j=0; j void sort(T[] a, Comparator c) {
        if (LegacyMergeSort.userRequested)
            legacyMergeSort(a, c);
        else
            TimSort.sort(a, c);
    }	
	
	// TimSort - sort 

    static  void sort(T[] a, Comparator c) {
        sort(a, 0, a.length, c);
    }
	
    static  void sort(T[] a, int lo, int hi, Comparator c) {
        if (c == null) {
            Arrays.sort(a, lo, hi);
            return;
        }

        rangeCheck(a.length, lo, hi);
        int nRemaining  = hi - lo;
        if (nRemaining < 2)
            return;  // Arrays of size 0 and 1 are always sorted

        // If array is small, do a "mini-TimSort" with no merges
        if (nRemaining < MIN_MERGE) {
            int initRunLen = countRunAndMakeAscending(a, lo, hi, c);
            binarySort(a, lo, hi, lo + initRunLen, c);
            return;
        }

        /**
         * March over the array once, left to right, finding natural runs,
         * extending short natural runs to minRun elements, and merging runs
         * to maintain stack invariant.
         */
        TimSort ts = new TimSort<>(a, c);
        int minRun = minRunLength(nRemaining);
        do {
            // Identify next run
            int runLen = countRunAndMakeAscending(a, lo, hi, c);

            // If run is short, extend to min(minRun, nRemaining)
            if (runLen < minRun) {
                int force = nRemaining <= minRun ? nRemaining : minRun;
                binarySort(a, lo, lo + force, lo + runLen, c);
                runLen = force;
            }

            // Push run onto pending-run stack, and maybe merge
            ts.pushRun(lo, runLen);
            ts.mergeCollapse();

            // Advance to find next run
            lo += runLen;
            nRemaining -= runLen;
        } while (nRemaining != 0);

        // Merge all remaining runs to complete sort
        assert lo == hi;
        ts.mergeForceCollapse();
        assert ts.stackSize == 1;
    }
	
	
	// TimeSort - countRunAndMakeAscending

    private static  int countRunAndMakeAscending(T[] a, int lo, int hi,
                                                    Comparator c) {
        assert lo < hi;
        int runHi = lo + 1;
        if (runHi == hi)
            return 1;
		// 此处用 a[1] 与 a[0] 进行比较
        // Find end of run, and reverse range if descending
        if (c.compare(a[runHi++], a[lo]) < 0) { // Descending
            while (runHi < hi && c.compare(a[runHi], a[runHi - 1]) < 0)
                runHi++;
            reverseRange(a, lo, runHi);
        } else {                              // Ascending
            while (runHi < hi && c.compare(a[runHi], a[runHi - 1]) >= 0)
                runHi++;
        }

        return runHi - lo;
    }