Sort objects in Java with case sensitive String key

Question

I have a requirement to sort objects(Zone) with their names(Zone Name : String) considering the case. I tried this with Java Comparator interface.

class NameComparator implements Comparator<Zone> {
    public int compare(Zone z1, Zone z2) {
        return z1.getZoneName().compareTo(z2.getZoneName());
   }
}

But this Comparator only sort lexicographically.

Ex : Required order for the zone names.

['Zone AAa3','Zone aaa3','Zone BBB7','Zone BBb7','Zone bbb7']

Current Output :

['Zone AAa3','Zone BBB7','Zone BBb7','Zone aaa3','Zone bbb7']

Is there any way to achieve this, other than writing a raw object sorting method?

erickson · Accepted Answer · 2016-06-16 16:40:47Z

10

There is a pre-defined comparator for case-insensitive sorting. You can use it with a Zone by extracting a sort key.

Comparator<Zone> byName = Comparator
    .comparing(Zone::getZoneName, String.CASE_INSENSITIVE_ORDER)
    .thenComparing(Zone::getZoneName);

edited Jun 16, 2016 at 16:40

answered Jun 6, 2016 at 4:15

erickson

271k59 gold badges407 silver badges502 bronze badges

Sign up to request clarification or add additional context in comments.

6 Comments

shamika Dharmasiri Over a year ago

This seems only work for Java 8.But looks like a easier way.Thank you.

erickson Over a year ago

@shamikaDharmasiri Well, Java 7 ended support (including security) over a year ago, and Java 9 is almost here. Getting current is worth some effort.

Subhrajyoti Majumder Over a year ago

But this does not solve the use case of ordering ('Zone AAa3' < 'Zone aaa3') - If input is Zone aaa3, Zone AAa3, then it does not return Zone AAa3, aaa3.

erickson Over a year ago

@SubhrajyotiMajumder Updated to handle that case.

Holger Over a year ago

Whenever you find yourself writing ::compareTo, you should rethink what you are doing. The presence of a compareTo method suggests the presence of a natural order which allows either, the use of Comparator.naturalOrder() or, in most cases, omitting the comparator entirely, i.e.

Comparator<Zone> byName = Comparator.comparing(Zone::getZoneName, String.CASE_INSENSITIVE_ORDER).thenComparing(Zone::getZoneName);

. Though in this specific case, you perhaps want to use Comparator.comparing(Zone::getZoneName, Collator.getInstance()) instead…

|

Subhrajyoti Majumder · Accepted Answer · 2016-06-06 06:20:29Z

1

Tweak the logic, convert both name to lower case or upper case and then compare.

public int compare(Zone z1, Zone z2){
  if(z1.getZoneName().toLowerCase().equals(z2.getZoneName().toLowerCase()))
      return z1.getZoneName().compareTo(z2.getZoneName());
  else
      return z1.getZoneName().toLowerCase().compareTo(z2.getZoneName().toLowerCase());
}

Using lambda -

Comparator<Zone> byName = (z1, z2)->{
    if(z1.getZoneName().toLowerCase().equals(z2.getZoneName().toLowerCase()))
       return z1.getZoneName().compareTo(z2.getZoneName());
    else
       return z1.getZoneName().toLowerCase().compareTo(z2.getZoneName().toLowerCase());
};

edited Jun 6, 2016 at 6:20

answered Jun 6, 2016 at 3:54

Subhrajyoti Majumder

41.3k13 gold badges84 silver badges103 bronze badges

3 Comments

shamika Dharmasiri Over a year ago

Then the case is not considered.I also need the case to be considered.I cannot assure this order, 'Zone AAa3' < 'Zone aaa3'

Subhrajyoti Majumder Over a year ago

updated answer - supported use case 'Zone AAa3' < 'Zone aaa3'

Holger Over a year ago

The conversion to lower case is an unnecessary waste of performance and may not cover all cases of Unicode letters. Mind the existence of String.compareToIgnoreCase(String) and String.equalsIgnoreCase(String) which perform exactly the desired operation.

Collectives™ on Stack Overflow

Sort objects in Java with case sensitive String key

2 Answers 2

6 Comments

3 Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

6 Comments

3 Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related