Sorting hashmap based on keys

Question

I have the following hashmap in java:

{B046=0.0, A061=3.0, A071=0.0, B085=0.0, B075=3.0, B076=9.0, B086=3.0, B095=0.0, B096=0.0, A052=0.0, B066=0.0, B056=9.0, B065=0.0, B055=9.0}

How should I go about sorting the hashmap such that the Alphabet, followed by the numerical figures are taken into account?

The resulting hashmap should look like this:

{A052=0.0,A061=3.0,A071=0.0,B046=0.0,B055=9.0,B056=9.0,B065=0.0,B066=0.0,B075=3.0,B076=9.0,B085=0.0,B086=3.0,B095=0.0,B096=0.0}

Appreciate the help!

Answer 1

Use sorted TreeMap:

Map<String, Float> map = new TreeMap<>(yourMap); 

It will automatically put entries sorted by keys. I think natural String ordering will be fine in your case.

Note that HashMap due to lookup optimizations does not preserve order.

Answer 2

Use a TreeMap with a custom comparator.

class MyComparator implements Comparator<String>     {         public int compare(String o1,String o2)         {             // Your logic for comparing the key strings         }     }  TreeMap<String, Float> tm = new TreeMap<String , Float>(new MyComparator()); 

As you add new elements, they will be automatically sorted.

In your case, it might not even be necessary to implement a comparator because String ordering might be sufficient. But if you want to implement special cases, like lower case alphas appear before upper case, or treat the numbers a certain way, use the comparator.