Sorting a list using custom parameters

Question

Here is my code :

import java.util.List;

import com.atlassian.jira.ComponentManager;
import com.atlassian.jira.bc.filter.SearchRequestService;
import com.atlassian.jira.issue.Issue;
import com.atlassian.jira.issue.search.SearchException;
import com.atlassian.jira.issue.search.SearchProvider;
import com.atlassian.jira.issue.search.SearchRequest;
import com.atlassian.jira.issue.search.SearchResults;
import com.atlassian.jira.web.bean.PagerFilter;


class IssueTest{

    String  id;
    String type;
    public String getId() {
        return id;
    }
    public void setId(String id) {
        this.id = id;
    }
    public String getType() {
        return type;
    }
    public void setType(String type) {
        this.type = type;
    }

    public IssueTest(String id,String type)
    {
        this.id = id;
        this.type = type;

    }


}


public class test {

    /**
     * @param args
     */

     static List<IssueTest> issues; 


    public static void main(String[] args) {
        // TODO Auto-generated method stub

        test t = new test();


    }

    public test ()
    {

        IssueTest i = new IssueTest("B-1", "bug");
        issues.add(i);
        IssueTest j = new IssueTest("S-1", "story");
        issues.add(j);
        IssueTest k = new IssueTest("T-1", "task");
        issues.add(k);
        IssueTest l = new IssueTest("T-2", "task");
        issues.add(l);
        IssueTest m = new IssueTest("E-1", "epic");
        issues.add(m);
        IssueTest n = new IssueTest("E-2", "epic");
        issues.add(n);
        IssueTest o = new IssueTest("T-3", "task");
        issues.add(o);
        IssueTest p = new IssueTest("S-2", "story");
        issues.add(p);
        IssueTest q = new IssueTest("B-2", "bug");
        issues.add(q);
        IssueTest r = new IssueTest("B-3", "bug");
        issues.add(r);

    }


}

I want to sort this list according to the "type" . I want all objects in the order of - tasks then bugs then story then epic

and the results you have gotten so far are what? Further what have you tried to validate that your implementation is correct / incorrect? — Woot4Moo
– Woot4Moo, Commented Aug 1, 2012 at 12:40

Louis Wasserman · Accepted Answer · 2012-08-01 12:52:37Z

3

You're going to need to write a custom Comparator to implement that ordering. This is going to be a bit complicated, unfortunately, without third-party libraries...especially if you're not on Java 7.

Comparator<IssueTest> comparator = new Comparator<IssueTest>() {
  private int getStringPosition(String str) {
    if(str.equals("task")) {
      return 0;
    } else if (str.equals("bug")) {
      return 1;
    } else if (str.equals("story")) {
      return 2;
    } else if (str.equals("epic")) {
      return 3;
    } else {
      throw new AssertionError();
    }
  }
  public int compare(IssueTest a, IssueTest b) {
    return getStringPosition(a.getType()) - getStringPosition(b.getType());
  }
};
Collections.sort(list, comparator);

If you used an enum instead of string types, this would be much easier, though.

If you can use third-party libraries, this might be a bit simpler with Guava:

Ordering<String> typeOrdering = Ordering.explicit("task", "bug", "story", "epic");
Ordering<IssueTest> issueTestOrdering =
 typeOrdering.onResultOf(new Function<IssueTest, String>() {
   public String apply(IssueTest it) {return it.getType(); }
 });
Collections.sort(list, issueTestOrdering);

(Disclosure: I contribute to Guava.)

edited Aug 1, 2012 at 12:52

answered Aug 1, 2012 at 12:41

Louis Wasserman

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1 Comment

Rish Over a year ago

I cannot use external libraries . Please can you show without this

gkuzmin · Accepted Answer · 2012-08-01 12:41:13Z

2

You can define a comparator method and use Collections.sort(lst), for example.

answered Aug 1, 2012 at 12:41

gkuzmin

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Comments

skrebbel · Accepted Answer · 2012-08-01 12:41:56Z

2

If that's the only way you want to ever sort a list of IssueTest objects, then the right way would be to implement Comparable.

It is well explained on http://docs.oracle.com/javase/tutorial/collections/interfaces/order.html

If you'd want to sort by different keys in different places, don't make IssueTest implement Comparable, but make a set of classes that implement Comparator<IssueTest>.

answered Aug 1, 2012 at 12:41

skrebbel

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Comments

Woot4Moo · Accepted Answer · 2012-08-01 12:44:04Z

1

public class IssueComparator implements Comparator<IssueTest>{

    @Override
    public int compare(IssueTest issue1, IssueTest issue2) {

        String type1 = issue1.getType();
        String type2 = issue2.getType();

        if (type1.length() > type2.length() ){
            return +1;
        }else if (type1.length() < type2.length() ){
            return -1;
        }else{
            return 0;
        }
    }

Obviously length is not an appropriate criterion to use, The above is to illustrate how an implementation of Comparator can be completed.

answered Aug 1, 2012 at 12:44

Woot4Moo

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2 Comments

Vala Over a year ago

It makes a lot more sense to use the compareTo method already present on the String class; type1.compareTo(type2). Of course, you may want to check for nulls and you may want to store it so you can check the other fields if the result is null.

Woot4Moo Over a year ago

@Thor84no sure equally valid point, I am assuming that String is the correct object type in his domain object. I did however want to give OP an explanation as to how Comparator can be implemented as it is important to know.

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