what is the better alternative to following if-else ladder in java?

Question

Situation : I am examining filenames , the filename is stored in a String variable called str and according to the conditions checked in if statements i am setting the value of a variable called mailType .

if(str.contains("template"))
        {                   
          if(str.contains("unsupported"))
              mailType="unsupported";      
              else
                  if(str.contains("final_result"))                
                      mailType="final_result";            
                  else
                      if(str.contains("process_success"))
                          mailType="Process Success"; 
                      else
                          if(str.contains("receive"))                         
                              mailType="Receive";                         
                          else
                          if(str.contains("sen"))
                              mailType="sent"; 
                          else
                              if(str.contains("welcome"))
                                  mailType="welcome";
                              else
                                  if(str.contains("manual"))
                                     mailType="Manual";                    
        }       
        else                
if(str.contains("properties"))
        {

          if(str.contains("unsupported"))
              mailType="unsupported";      
              else
                  if(str.contains("final_result"))                
                      mailType="final_result";            
                  else
                      if(str.contains("process_success"))
                          mailType="Process Success"; 
                      else
                          if(str.contains("receive"))                         
                              mailType="Receive";                         
                          else
                          if(str.contains("sen"))
                              mailType="sent"; 
                          else
                              if(str.contains("welcome"))
                                  mailType="welcome";
                              else
                                  if(str.contains("manual"))
                                     mailType="Manual";

        }

Problem : Is there any better way to do this in java that shortens my code and is memory friendly ?

Answer 1

Use a LinkedHashMap<String, String>:

LinkedHashMap<String, String> mapping = new LinkedHashMap<>();
mapping.put("unsupported", "unsupported");
mapping.put("final_result", "final_result");
// ... etc

Then iterate the map until you find a matching key:

for (Map.Entry<String, String> entry : mapping.entrySet()) {
  if (str.contains(entry.getKey()) {
    mailType = entry.getValue();
    break;
  }
}

The key point here is that LinkedHashMap preserves insertion order (unlike HashMap) so you can actually specify the order in which you want to test for matches (other map implementations do this too, e.g. Guava's ImmutableMap; LinkedHashMap is simply one that you have out of the box).

If you need to nest this for the outer cases, you can simply apply the same pattern:

LinkedHashMap<String, LinkedHashMap<String, String>> outerMapping =
    new LinkedHashMap<>();
outerMapping.put("template", mapping);
outerMapping.put("properties", someOtherMapping);

And then just iterate through the keys in the same way:

for (Map.Entry<String, LinkedHashMap<String, String>> outerEntry : outerMapping.entrySet()) {
  if (str.contains(outerEntry.getKey()) {
    // Apply the iteration above, using outerEntry.getValue().
  }
}