Java array sorting of last names then age

Question

I wrote a program using sorting to first sort an array list by the last name of the entries and then by there age, thus creating 2 lists as the output. The problem is the last name sort seems to work good but the age sort always puts the names in the same order as the last name sort. Here is my code so far, I have 2 classes.

package myperson;

import java.util.ArrayList;
import java.util.Collections;
import java.util.Scanner;

public class Queue implements Comparable<Queue> {
public Person Data;
public int iter=0;
public Queue(String first, String last,int age)
{
Data = new Person(first, last, age);
}
@Override
public int compareTo(Queue other)
{
if(iter==0){
iter++;
return Data.Last.compareTo(other.Data.Last);
}
else
return Double.compare(Data.Age, other.Data.Age);
}
@Override
public String toString() {

return Data.First + " " + Data.Last;
}
public static void main(String[] args) throws java.io.IOException {
ArrayList list = new ArrayList();
String first;
String last;
int age = 0;
Scanner sc=new Scanner(System.in);

list.add(new Queue("John", "Huber", 22));
list.add(new Queue("Chelsea", "Davis", 32));
list.add(new Queue("Susan", "Taylor", 46));
list.add(new Queue("Scott", "Zedburg", 59));

System.out.println("Ordered by Last Name");
Collections.sort(list);
for (int i = 0; i < list.size(); i++)
{
System.out.println(list.get(i));
}
System.out.println("\nSort by Age");
Collections.sort(list);
for (int i = 0; i < list.size(); i++)
{
System.out.println(list.get(i));
}
}
}

Person class:

 package myperson;
    public class Person {
    public String First;
    public String Last;
    public double Age;
    public Person(String first, String last,double age)
    {
    First = first;
    Last = last;
    Age = age;
    }  
    }

Output:

run:

  Ordered by Last Name

Chelsea Davis

John Huber

Susan Taylor

Scott Zedburg

  Sort by Age

Chelsea Davis

John Huber

Susan Taylor

Scott Zedburg

BUILD SUCCESSFUL (total time: 0 seconds)

First of all variable names should NOT start with an upper case character. Follow Java conventions. For sorting with different Comparators check out:: https://stackoverflow.com/questions/28008497/sort-by-name-object-java/28012014#28012014 — camickr, Apr 08 '18 at 23:13
Please use proper indentation. Your code is hard to read otherwise. — Zabuzard, Apr 08 '18 at 23:48
The supposedly 'duplicate' answer does not answer this question. That is about sorting by multiple criteria in the same operation. This is about sorting multiple times by different criteria. — sprinter, Apr 09 '18 at 07:05

score 1 · Answer 1 · answered Apr 08 '18 at 23:32

You have a lot of issues in this code unfortunately. You are trying to use a variable inside your comparison function to change its behaviour. This breaks a number of rules concerning how comparison functions should work. Read the documentation for Comparable for the full set of rules and conventions.

A much better approach is to specify the comparison function in the call to sort. Your final sorting code should look something like this:

List<Person> people = new ArrayList<>();
...

people.sort(Comparator.comparing(Person::getName));
...
people.sort(Comparator.comparingInt(Person::getAge));

Java array sorting of last names then age

1 Answers1