Java get String CompareTo as a comparator object

Question

I would like to sort and binary search a static array of strings via the String CompareTo comparator   The problem is that both sorting  and binary searching requires that a Comparator object be passed in -- So how do I pass in the built in string comparator

User · Accepted Answer

The Arrays class has versions of sort   and binarySearch   which don t require a Comparator  For example  you can use the version of Arrays sort   which just takes an array of objects  These methods call the compareTo   method of the objects in the array

User · Answer

Again  don t need the comparator for Arrays binarySearch Object   a  Object key  so long as the types of objects are comparable  but with lambda expressions this is now way easier   Simply replace the comparator with the method reference  String  compareTo  E g    Arrays binarySearch someStringArray   The String to find    String  compareTo     You could also use  Arrays binarySearch someStringArray   The String to find     a b  - gt  a compareTo b      but even before lambdas  there were always anonymous classes   Arrays binarySearch                  someStringArray                   The String to find                    new Comparator lt String gt                           Override                     public int compare String o1  String o2                            return o1 compareTo o2

User · Answer

You can use the StringUtils compare  a    b

User · Answer

Ok this is a few years later but with java 8 you can use Comparator naturalOrder       http   docs oracle com javase 8 docs api java util Comparator html naturalOrder--  From javadoc   static  lt T extends Comparable lt   super T gt  gt  Comparator lt T gt  naturalOrder     Returns a comparator that compares Comparable objects in natural order  The returned comparator is serializable and throws NullPointerException when comparing null

User · Answer

Solution for Java 8 based on java util Comparator comparing        Comparator lt String gt  c   Comparator comparing String  toString     or  Comparator lt String gt  c   Comparator comparing  String x  - gt  x

User · Answer

Also  if you want case-insensitive comparison  in recent versions of Java the String class contains a public static final field called CASE INSENSITIVE ORDER which is of type Comparator lt String gt   as I just recently found out  So  you can get your job done using String CASE INSENSITIVE ORDER

User · Answer

Regarding Nambari s answer there was a mistake  If you compare values using double equal sign    program will never reach compare method  unless someone will use new keyword to create String object which is not the best practice  This might be a bit better solution   public int compare String o1  String o2            if  o1    null  amp  amp  o2    null  return 0           if  o1    null    return -1           if  o2    null    return 1           return o1 compareTo o2           P S  Thanks for comments

User · Answer

We can use the String CASE INSENSITIVE ORDER comparator to compare the strings in case insensitive order   Arrays binarySearch someStringArray   The String to find   String CASE INSENSITIVE ORDER

User · Answer

To generalize the good answer of Mike Nakis with String CASE INSENSITIVE ORDER  you can also use    Collator getInstance      See Collator

User · Answer

This is a generic Comparator for any kind of Comparable object  not just String   package util   import java util Comparator          The Default Comparator for classes implementing Comparable         param  lt E gt  the type of the comparable objects         author Michael Belivanakis  michael gr      public final class DefaultComparator lt E extends Comparable lt E gt  gt  implements Comparator lt E gt         SuppressWarnings   rawtypes        private static final DefaultComparator lt   gt  INSTANCE   new DefaultComparator                    Get an instance of DefaultComparator for any type of Comparable                 param  lt T gt  the type of Comparable of interest                 return an instance of DefaultComparator for comparing instances of the requested type              public static  lt T extends Comparable lt T gt  gt  Comparator lt T gt  getInstance                  SuppressWarnings  unchecked           Comparator lt T gt  result    Comparator lt T gt  INSTANCE          return result             private DefaultComparator                     Override     public int compare  E o1  E o2                 if  o1    o2               return 0          if  o1    null               return 1          if  o2    null               return -1          return o1 compareTo  o2              How to use with String   Comparator lt String gt  stringComparator   DefaultComparator getInstance

User · Answer

You may write your own comparator  public class ExampleComparator  implements Comparator lt String gt      public int compare String obj1  String obj2        if  obj1    obj2            return 0            if  obj1    null            return -1            if  obj2    null            return 1            return obj1 compareTo obj2

User · Answer

If you do find yourslef needing a Comparator  and you already use Guava  you can use Ordering natural

[java] Java get String CompareTo as a comparator object

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