Get specific element with highest value in ArrayList

Question

I'm new to java and I'm having a problem with ArrayList. I want to get the highest value from Jozef and Klaus.

ArrayList looks like:

|  Name        | Age|
+--------------+----+
| Jozef Coin   | 55 |    
| Jozef Coin   | 56 |    
| Jozef Coin   | 57 |
| Klaus Neumer | 34 |
| Klaus Neumer | 31 |
| Klaus Neumer | 59 |

This is my code so far, it only returns the highest value in the arraylist.

Person b = persons.get(0)

for(Person p: persons){    
      if(p.getAge() >= b.getAge()){    
         b = p;    
           System.out.println(b.toString());    
      }    
}

I'm probably way over my head but I'd love to know if this is possible and if so there is an solution to this.

Could you please clarify your question? What does the Person class look like? — Maljam
– Maljam, Commented Apr 3, 2016 at 4:57
So instead of highest in the list you want highest for each person? — Sam Orozco
– Sam Orozco, Commented Apr 3, 2016 at 5:00

Shree Krishna · Accepted Answer · 2016-04-03 05:03:48Z

3

You can use Comparable for your task

public class CompareAge implements Comparator<Person> {
    @Override
    public int compare(Person p1, Person p2) {
        return p1.getAge().compareTo(p2.getAge());
    }
}

Then use that CompareAge class like as follows

Collections.sort(myArrayList, new CompareAge());
myArrayList.get(arrayList.size() - 1); //Retrieve the last object

answered Apr 3, 2016 at 5:03

Shree Krishna

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1 Comment

Ilja Over a year ago

Thanks, this was a great solution to the problem.

Austin · Accepted Answer · 2016-04-03 05:02:39Z

0

It's hard to answer unless we know the methods in the Person class, however this would be the general way I would do it.

Person b = persons.get(0)
int jozefHighest = 0;
int klausHighest = 0;

for(Person p: persons){

      if(p.getName().startsWith("Jozef") {
        if(p.getAge() > jozefHighest)
            jozefHighest = p.getAge)_
      } else if (p.getName().startsWith("Klaus")) {
        if(p.getAge() > klausHighest)
            klausHighest = p.getAge()
      }

}

answered Apr 3, 2016 at 5:02

Austin

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Comments

Suparna · Accepted Answer · 2016-04-03 05:07:38Z

0

Java 8 is Cool!

    int[] a = {1,2,3,4};
    OptionalInt maxValue = IntStream.of(a).max();
    System.out.println("Max Value: " + maxValue);

answered Apr 3, 2016 at 5:07

Suparna

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Comments

sprinter · Accepted Answer · 2016-04-03 05:57:56Z

0

You can do this in a single step in Java 8:

Map<String, Integer> oldestMap = persons.stream()
    .collect(Collectors.groupingBy(Person::getName,
        Collectors.maxBy(Person::getAge).get());

You now have a map from name to maximum age.

answered Apr 3, 2016 at 5:57

sprinter

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