Sort a list of Comparables using multiple string fields in a custom order

With this class:

public class MyClass implements Comparable<MyClass> {

private String status;
private String name;
private String firstName;

@Override
public int compareTo(MyClass o) {
return 0;
}

}


I'd like to sort a list of MyClass objects with this order:

How can I do this with the Comparable interface ?

Comparable

Well, what have you tried so far?
– Laurens
Jun 29 at 9:29

stackoverflow.com/questions/369512/… I tried the third answer in this post assuming I'm not using java 8. My filters are not the same, I don't know how to check by "keys"
– whySoSerious
Jun 29 at 9:32

Are these the only available names? I.e. toto, titi, tutu, tata? If not, then what's the general rule for sorting? Anyway, here is how you can use the comparator: List<MyClass> list = ...; Collections.sort(list);
– Tamas Rev
Jun 29 at 9:38

toto

titi

tutu

tata

List<MyClass> list = ...; Collections.sort(list);

2 Answers
2

I would do this like so: first define a set of lists which define the order for each field:

private static List<String> statusOrder = Arrays.asList("open", "working", "close");
private static List<String> nameOrder = Arrays.asList("toto", "titi");
private static List<String> firstNameOrder = Arrays.asList("tutu", "tata");


Then use List.indexOf to get the position of the element in the list, and then simply subtract the results:

List.indexOf

@Override
public int compareTo(MyClass o) {
final int statusComp = statusOrder.indexOf(status) - statusOrder.indexOf(o.status);
if (statusComp != 0) return statusComp;
final int nameComp = nameOrder.indexOf(name) - nameOrder.indexOf(o.name);
if (nameComp != 0) return nameComp;
return firstNameOrder.indexOf(firstName) - firstNameOrder.indexOf(o.firstName);
}


The issue with this approach is that indexOf will return -1 if the element is not in the list. You would need to define the behaviour in the case where MyClass contains non-standard values (perhaps it will never happen).

indexOf

MyClass

@DidierL I thought the agreement was sarcastic? I don't see it as an exact duplicate. That question wants to sort multiple string fields alphabetically, this question wants to sort multiple string fields, each with a defined non-alphabetic order. I've tried to improve the question to make it a clearer non-dupe.
– Michael
Jun 29 at 9:53

Ok, let's leave it open then.
– Didier L
Jun 29 at 12:12

I wrote you a class. It has a main method, so you can run it. The main method fills a list with MyClass objects, prints them, sorts them and prints them again:

import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.List;

public class MyClass implements Comparable<MyClass> {

private static class STATUS {
public static final String OPEN = "open";
public static final String WORKING = "working";
public static final String CLOSE = "close";
}

private static class NAME {
public static final String TOTO = "toto";
public static final String TITI = "titi";
}

private static class FIRST_NAME {
public static final String TUTU = "tutu";
public static final String TATA = "tata";
}

public MyClass(String status, String name, String firstName) {
this.status = status;
this.name = name;
this.firstName = firstName;
}

private String status;

private String name;

private String firstName;

@Override
public int compareTo(MyClass o) {
if(!equals(this.status, o.status)) {
return getIndex_status(this.status) - getIndex_status(o.status);
} else if(!equals(this.name, o.name))
return getIndex_name(this.name) - getIndex_name(o.name);
return getIndex_firstName(this.firstName) - getIndex_firstName(o.firstName);
}

private int getIndex_status(String status) {
return getIndex(status, new String {STATUS.OPEN, STATUS.WORKING, STATUS.CLOSE});
}

private int getIndex_name(String name) {
return getIndex(name, new String {NAME.TOTO, NAME.TITI});
}

private int getIndex_firstName(String firstName) {
return getIndex(firstName, new String {FIRST_NAME.TUTU, FIRST_NAME.TATA});
}

private int getIndex(String value, String values) {
int index = Arrays.asList(values).indexOf(value);
return index == -1 ? values.length : index;
}

@Override
public String toString() {
return "status: " + this.status + " | name: " + this.name + " | firstName: " + this.firstName;
}

public static void main(String args) {
List<MyClass> myObjects = new ArrayList<>();

myObjects.add(new MyClass(STATUS.WORKING, "aName", "aFirstName"));
myObjects.add(new MyClass(STATUS.OPEN, "aName", "aFirstName"));
myObjects.add(new MyClass(STATUS.CLOSE, "aName", "aFirstName"));
myObjects.add(new MyClass(STATUS.CLOSE, "aName", null));
myObjects.add(new MyClass(STATUS.CLOSE, NAME.TITI, "aFirstName"));
myObjects.add(new MyClass(STATUS.CLOSE, NAME.TOTO, "aFirstName"));
myObjects.add(new MyClass(STATUS.CLOSE, null, "aFirstName"));
myObjects.add(new MyClass(STATUS.CLOSE, "aName", FIRST_NAME.TATA));
myObjects.add(new MyClass(null, "aName", FIRST_NAME.TATA));
myObjects.add(new MyClass(STATUS.CLOSE, "aName", FIRST_NAME.TUTU));

System.out.println("before sorting:");
print(myObjects);
Collections.sort(myObjects);
System.out.println("after sorting:");
print(myObjects);
}

private static void print(List<MyClass> myObjects) {
for(MyClass myObject : myObjects) {
System.out.println(myObject);
}
}

private static boolean equals(String s1, String s2) {
if(s1 == null)
return s2 == null;
return s1.equals(s2);
}

}


why the downvote?
– Tom
12 hours ago

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