Android-java- How to sort a list of objects by a specific value inside an object

Question

Im trying to sort an arrailist of objects by a specific value inside the object. What would be the best approach to such things. Should I use Collections.sort () with some sort of comparator?

Im trying to sort a list of objects by a floating-point value that they store in one of the variables.

EDIT: This is what I have so far:

public class CustomComparator implements Comparator<Marker> { @Override public int compare(Mark o1, Mark o2) { return o1.getDistance().compareTo(o2.getDistance()); } } 

error state: cannot call compareTo (double) in a double type primitive.

Is it because the comparator cannot return anything other than a specific type?

Answer 1

You should use Comparable instead of Comparator, if the default sort is what you are looking for.

See here, this can be useful - When should a class be comparable and / or a comparator?

Try it -

 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<ToSort> sortList = new ArrayList<ToSort>(); 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<ToSort> { 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() > f.val.floatValue()) { return 1; } else if (val.floatValue() < f.val.floatValue()) { return -1; } else { return 0; } } @Override public String toString(){ return this.id; } } 

Answer 2

Follow this code to sort any ArrayList

 Collections.sort(myList, new Comparator<EmployeeClass>(){ 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(obj2.empId); // To compare integer values // ## Descending order // return obj2.firstName.compareToIgnoreCase(obj1.firstName); // To compare string values // return Integer.valueOf(obj2.empId).compareTo(obj1.empId); // To compare integer values } }); 

Answer 3

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<Person> list = new ArrayList<Person>(); 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()); } }); 

Answer 4

Now there is no need for boxing (there is no need to create an OBJECT using the new operator usage value, if set using CompareTo of Collections.Sort ..)

1) In ascending order

 Collections.sort(temp, new Comparator<XYZBean>() { @Override public int compare(XYZBean lhs, XYZBean rhs) { return Integer.valueOf(lhs.getDistance()).compareTo(rhs.getDistance()); } }); 

1) For decaine order

 Collections.sort(temp, new Comparator<XYZBean>() { @Override public int compare(XYZBean lhs, XYZBean rhs) { return Integer.valueOf(rhs.getDistance()).compareTo(lhs.getDistance()); } }); 

Answer 5

"Android-java" here is by no means different from "normal java", so yes Collections.sort() would be a good approach.

Answer 6

 public class DateComparator implements Comparator<Marker> { @Override public int compare(Mark lhs, Mark rhs) { Double distance = Double.valueOf(lhs.getDistance()); Double distance1 = Double.valueOf(rhs.getDistance()); if (distance.compareTo(distance1) < 0) { return -1; } else if (distance.compareTo(distance1) > 0) { return 1; } else { return 0; } } } ArrayList(Marker) arraylist; 

How to use:

 Collections.sort(arraylist, new DateComparator()); 

Answer 7

Either make a Comparator that can compare your objects, or if they are all instances of the same class, you can make this class Comparable . Then you can use Collections.sort () to actually sort.

Answer 8

You can compare two lines using this.

 Collections.sort(contactsList, new Comparator<ContactsData>() { @Override public int compare(ContactsData lhs, ContactsData rhs) { char l = Character.toUpperCase(lhs.name.charAt(0)); if (l < 'A' || l > 'Z') l += 'Z'; char r = Character.toUpperCase(rhs.name.charAt(0)); if (r < 'A' || r > 'Z') r += 'Z'; String s1 = l + lhs.name.substring(1); String s2 = r + rhs.name.substring(1); return s1.compareTo(s2); } }); 

And now create the 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 is the contact list:

 public static ArrayList<ContactsData> contactsList = new ArrayList<ContactsData>(); 

Answer 9

I have a list that shows information about all clients. I sort the client name using this custom comparator class. They have extra lyres besides English letters, which I control this SetStrength command (Collator.SECONDARY)

  public class CustomNameComparator implements Comparator<ClientInfo> { @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" < "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" < "às" < "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" < "Ao" < "aò"). 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="< å,Å< ä,Ä< a,A< b,B< c,C< d,D< é< e,E< f,F< g,G< h,H< ï< i,I"+"< j,J< k,K< l,L< m,M< n,N< ö,Ö< o,O< p,P< q,Q< r,R"+"< s,S< t,T< ü< u,U< v,V< w,W< x,X< y,Y< 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);*/ 

Answer 10

Model Class:

 public class ToDoModel implements Comparable<ToDoModel> { 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 the data to ArrayList

 for (int i = 0; i < 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 sorts data by date