Sorting Array of Custom Object in Java

Question

I am trying to sort the Project end times from smallest to largest values.

I have created a list of custom objects called Project and am attempting to sort them based on a value returned by an accessor. I have overloaded the compare function and am receiving the error:

The method sort(List, Comparator) in the type Collections is not applicable for the arguments (Project[], new Comparator(){})

The code from my main is shown below, any and all help appreciated.

Collections.sort(projectList, new Comparator< Project>(){

    @Override
    public int compare(Project project1, Project project2)
    {   
       return compareProjects(project1, project2);}
    }
);

public static int compareProjects(Project project1, Project project2)
{ 
    if (project1.getEndTime() > project2.getEndTime())
        return 1;
    else
        return 0;
}

and my Project Class:

public Project(int projectNum, int start, int end)
{
    this.projectNum = projectNum;
    this.start = start;
    this.end = end;
    this.length = end - start;
}

public static int getEndTime()
{
    return end;
}

You could just use return project1.getEndTime() - project2.getEndTime() ... but what's the question? — MadProgrammer
– MadProgrammer, Commented Oct 30, 2015 at 4:54
is not applicable for the arguments (Project[], new Comparator(){}) I'm pretty sure that your answer right there. Project[] is an array, not a list. — markspace
– markspace, Commented Oct 30, 2015 at 4:59

Ankur Singhal · Accepted Answer · 2015-10-30 04:59:20Z

4

Collections.sort operates on a List, and Arrays.sort operates on an array

Need to changes Project.class , implement Comparable interface

class Project implements Comparable<Project> {

    @Override
    public int compareTo(Project o) {
        if (this.getEndTime() > o.getEndTime())
        return 1;
    else
        return 0;
    }
}

Then in your main.class

Arrays.sort(projectList);

answered Oct 30, 2015 at 4:59

Ankur Singhal

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Comments

Elliott Frisch · Accepted Answer · 2015-10-30 05:00:08Z

0

You never return -1 (e.g <). However, I would suggest you use Integer.compareTo(int, int) which returns the value 0 if x == y; a value less than 0 if x < y; and a value greater than 0 if x > y like

public static int compareProjects(Project project1, Project project2) {
    return Integer.compare(project1.getEndTime(), project2.getEndTime());
}

Also, since projectList is an array of Project you can get it as a List<Project> with Arrays.asList(T...) like

Collections.sort(Arrays.asList(projectList),

answered Oct 30, 2015 at 5:00

Elliott Frisch

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