Android-java- How to sort a list of objects by a certain value within the object

Question

Im trying to sort through an arraylist of objects by a particular value within the object  What would be the best approach to do such a thing  Should I use Collections sort   with some kind of comparator    Im trying to sort a list of objects by a float value they hold in one of the variables   EDIT  This is what I have so far   public class CustomComparator implements Comparator lt Marker gt         Override     public int compare Mark o1  Mark o2            return o1 getDistance   compareTo o2 getDistance               the error states  Cannot invoke compareTo double  on the primitive type double   Is it because a comparator cant return anything other than a certain type

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It s very easy for Kotlin   listToBeSorted sortBy   it distance

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Now no need to Boxing  i e no need to Creating OBJECT using new Operator use valueOf insted with compareTo of Collections Sort     1 For Ascending order  Collections sort temp  new Comparator lt XYZBean gt             Override      public int compare XYZBean lhs  XYZBean rhs            return Integer valueOf lhs getDistance    compareTo rhs getDistance                    1 For Deascending order  Collections sort temp  new Comparator lt XYZBean gt             Override      public int compare XYZBean lhs  XYZBean rhs            return Integer valueOf rhs getDistance    compareTo lhs getDistance

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I think this will help you better   Person p   new Person  Bruce    Willis    Person p1    new Person  Tom    Hanks    Person p2   new Person  Nicolas    Cage    Person p3   new Person  John    Travolta     ArrayList lt Person gt  list   new ArrayList lt Person gt     list add p   list add p1   list add p2   list add p3    Collections sort list  new Comparator          Override     public int compare Object o1  Object o2            Person p1    Person  o1          Person p2    Person  o2          return p1 getFirstName   compareToIgnoreCase p2 getFirstName

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Follow this code to sort any ArrayList  Collections sort myList  new Comparator lt EmployeeClass gt         public int compare EmployeeClass obj1  EmployeeClass obj2                  Ascending order         return obj1 firstName compareToIgnoreCase obj2 firstName      To compare string values            return Integer valueOf obj1 empId  compareTo Integer valueOf obj2 empId       To compare integer values                Descending order            return obj2 firstName compareToIgnoreCase obj1 firstName      To compare string values            return Integer valueOf obj2 empId  compareTo Integer valueOf obj1 empId       To compare integer values

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You can compare two String by using this   Collections sort contactsList  new Comparator lt ContactsData gt                            Override                     public int compare ContactsData lhs  ContactsData rhs                             char l   Character toUpperCase lhs name charAt 0                             if  l  lt   A     l  gt   Z                                l     Z                            char r   Character toUpperCase rhs name charAt 0                             if  r  lt   A     r  gt   Z                                r     Z                            String s1   l   lhs name substring 1                            String s2   r   rhs name substring 1                            return s1 compareTo s2                                                 And Now make a ContactData Class   public class ContactsData    public String name  public String id  public String email  public String avatar   public String connection type  public String thumb  public String small  public String first name  public String last name  public String no of user  public int grpIndex   public ContactsData String name  String id  String email  String avatar  String connection type        this name   name      this id   id      this email   email      this avatar   avatar      this connection type   connection type         Here contactsList is    public static ArrayList lt ContactsData gt  contactsList   new ArrayList lt ContactsData gt

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Either make a Comparator that can compare your objects  or if they are all instances of the same class  you can make that class implement Comparable  You can then use Collections sort   to do the actual sorting

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I have a listview which shows the Information about the all clients I am sorting the clients name using this custom comparator class  They are having some extra lerret apart from english letters which  i am managing with this setStrength Collator SECONDARY    public class CustomNameComparator implements Comparator lt ClientInfo gt             Override      public int compare ClientInfo o1  ClientInfo o2              Locale locale Locale getDefault            Collator collator   Collator getInstance locale           collator setStrength Collator SECONDARY           return collator compare o1 title  o2 title              PRIMARY strength  Typically  this is used to denote differences between base characters  for example   a   lt   b    It is the strongest difference  For example  dictionaries are divided into different sections by base character   SECONDARY strength  Accents in the characters are considered secondary differences  for example   as   lt     s   lt   at    Other differences between letters can also be considered secondary differences  depending on the language  A secondary difference is ignored when there is a primary difference anywhere in the strings   TERTIARY strength  Upper and lower case differences in characters are distinguished at tertiary strength  for example   ao   lt   Ao   lt   a      In addition  a variant of a letter differs from the base form on the tertiary strength  such as  A  and       Another example is the difference between large and small Kana  A tertiary difference is ignored when there is a primary or secondary difference anywhere in the strings   IDENTICAL strength  When all other strengths are equal  the IDENTICAL strength is used as a tiebreaker  The Unicode code point values of the NFD form of each string are compared  just in case there is no difference  For example  Hebrew cantellation marks are only distinguished at this strength  This strength should be used sparingly  as only code point value differences between two strings are an extremely rare occurrence  Using this strength substantially decreases the performance for both comparison and collation key generation APIs  This strength also increases the size of the collation key      Here is a another way to make a rule base sorting if u need it just sharing            String rules   lt        lt        lt  a A lt  b B lt  c C lt  d D lt     lt  e E lt  f F lt  g G lt  h H lt     lt  i I    lt  j J lt  k K lt  l L lt  m M lt  n N lt        lt  o O lt  p P lt  q Q lt  r R    lt  s S lt  t T lt     lt  u U lt  v V lt  w W lt  x X lt  y Y lt  z Z           RuleBasedCollator rbc   null          try               rbc   new RuleBasedCollator rules             catch  ParseException e                   TODO Auto-generated catch block             e printStackTrace                      String myTitles    o1 title o2 title           Collections sort Arrays asList myTitles   rbc

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You should use Comparable instead of a Comparator if a default sort is what your looking for   See here  this may be of some help - When should a class be Comparable and or Comparator   Try this -   import java util ArrayList  import java util Collections  import java util List   public class TestSort        public static void main String args              ToSort toSort1   new ToSort new Float 3    3            ToSort toSort2   new ToSort new Float 6    6            ToSort toSort3   new ToSort new Float 9    9            ToSort toSort4   new ToSort new Float 1    1            ToSort toSort5   new ToSort new Float 5    5            ToSort toSort6   new ToSort new Float 0    0            ToSort toSort7   new ToSort new Float 3    3            ToSort toSort8   new ToSort new Float -3    -3             List lt ToSort gt  sortList   new ArrayList lt ToSort gt             sortList add toSort1           sortList add toSort2           sortList add toSort3           sortList add toSort4           sortList add toSort5           sortList add toSort6           sortList add toSort7           sortList add toSort8            Collections sort sortList            for ToSort toSort   sortList               System out println toSort toString                         public class ToSort implements Comparable lt ToSort gt         private Float val      private String id       public ToSort Float val  String id           this val   val          this id   id              Override     public int compareTo ToSort f             if  val floatValue    gt  f val floatValue                  return 1                    else if  val floatValue    lt   f val floatValue                  return -1                    else               return 0                         Override     public String toString            return this id

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For Kotlin  you can use this function  fun sortList list  List lt YourCustomPOJOClass  gt            descending     Collections sort          list         o1  o2 - gt  Integer valueOf o1   intValueXYZ    compareTo o2   intValueXYZ               ascending       Collections sort            list           o1  o2 - gt  Integer valueOf o2   intValueXYZ    compareTo o1   intValueXYZ          and just call it in your activity or fragment by  sortList list

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public class DateComparator implements Comparator lt Marker gt         Override     public int compare Mark lhs  Mark rhs            Double distance   Double valueOf lhs getDistance             Double distance1   Double valueOf rhs getDistance             if  distance compareTo distance1   lt  0                return -1            else if  distance compareTo distance1   gt  0                return 1            else               return 0                     ArrayList Marker  arraylist    How To use   Collections sort arraylist  new DateComparator

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Model Class    public class ToDoModel implements Comparable lt ToDoModel gt        private String id      private Date taskDate       public String getId             return id             public void setId String id            this id   id             public Date getTaskDate             return taskDate             public void setTaskDate Date taskDate            this taskDate   taskDate              Override     public int compareTo ToDoModel another            return getTaskDate   compareTo another getTaskDate                 Now set data in ArrayList  for  int i   0  i  lt  your array length  i          ToDoModel tm   new ToDoModel        tm setId your id       tm setTaskDate your date       mArrayList add tm       Now Sort ArrayList  Collections sort toDoList     Summary  It will sort your data datewise

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Android-java  is here by no means different than  normal java   so yes Collections sort   would be a good approach

[java] Android-java- How to sort a list of objects by a certain value within the object

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