使用自定义比较器（如Excel坐标顺序）订购TreeMap

Question

I'm using a TreeMap and its subMap to manage Excel files. I use as key the Excel coordinate.

In Excel the order is like A , B , C , ..., AA , AB , AC , ..., BA ... but the order I have is A , AA , AAA , AB , ..., B .

I thought the solution is to use a custom comparator but I don't know how to make it to obtain Excel alphabetical order.

Comparator<String> excelOrder= new Comparator<String>() {
    @Override public int compare(String s1, String s2) {
        //make order
    }           
};

and then use

   SortedMap<String,String> map = new TreeMap<String,String>(secondCharComparator);

Answer 1

First, you want to compare the String by their length (using String.length() ) and then lexicographically (this is exactly what's done by default with String.compareTo(other) ). The following does exactly that:

Comparator<String> excelOrder = new Comparator<String>() {
    @Override
    public int compare(String s1, String s2) {
       int s1Length = s1.length();
       int s2Length = s2.length();
       if (s1Length < s2Length) {
           return -1;
       } else if (s1Length > s2Length) {
           return 1;
       } else {
           return s1.compareTo(s2);
       }
    }           
};

Note that if you are using Java 8, this can be written a lot more simply (this code is using the following static import import static java.util.Comparator.comparingInt; ):

Comparator<String> excelOrder = comparingInt(String::length).thenComparing(String::compareTo);