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edit: @Misha's answer is a welcome improvement to mine, do take a look at that too.

edit: @Misha's answer is a welcome improvement to mine, do take a look at that too.

edit: @Misha 's answer is a welcome improvement to mine, do take a look at that too.

• Java's bracing convention is to put the opening brace on the same line, instead of what you have used (mostly). More importantly, have a consistent convention in your codebase. :) If you are more inclined to your current way, then do so throughout.

• HashMap<Character, Integer> map should be declared using the Map interface, for simplification.

• The method name getMaxViaHashmap() can be improved upon, as there should not be a need to tell callers how the derivation is done (ViaHashmap).

• If your method is meant to be used solely for the derivation, it should not print output to `System.out. From my example above, I get the results out first, then display it to the user.

• Even if you want to do the equivalent of this manually:

   if (map.containsKey(key)) {
   map.put(key, map.get(key) + newValue);
   } else {
   map.put(key, newValue);
   }
  

  There are the newer Map.compute() or Map.merge() methods to help you. For example:

   // input being the String
   Map<Character, Long> result = new HashMap<>();
   for (int i = 0; i < input.length(); i++) {
   result.merge(Character.valueOf(input.charAt(i)), 1L, (a, b) -> a + b);
   }
  

• Java's bracing convention is to put the opening brace on the same line, instead of what you have used (mostly). More importantly, have a consistent convention in your codebase. :) If you are more inclined to your current way, then do so throughout.

• HashMap<Character, Integer> map should be declared using the Map interface, for simplification.

• The method name getMaxViaHashmap() can be improved upon, as there should not be a need to tell callers how the derivation is done (ViaHashmap).

• If your method is meant to be used solely for the derivation, it should not print output to System.out. From my example above, I get the results out first, then display it to the user.

• Even if you want to do the equivalent of this manually:

   if (map.containsKey(key)) {
   map.put(key, map.get(key) + newValue);
   } else {
   map.put(key, newValue);
   }
  

  There are the newer Map.compute() or Map.merge() methods to help you. For example:

   // input being the String
   Map<Character, Long> result = new HashMap<>();
   for (int i = 0; i < input.length(); i++) {
   result.merge(Character.valueOf(input.charAt(i)), 1L, (a, b) -> a + b);
   }