Sorting through ArrayList of Objects, Add given Instance to ArrayList of given instances issue

Question

I'm getting the error

no suitable method found for add(Object), method Collected.add(Student is not applicable)

when I try the following code. I swear I've done it this way before? So confused. Appreciate any insights. Cheers

    //Sort and display list of Student objects by sortBy (surname or id)
public static void sortAndDisplayStudents(String sortBy, ArrayList<Object> objList) {
    ArrayList<Student> students = new ArrayList<>();

    //Add all Objcets in objList that are a Student
    for(Object s: objList) {
        if(s instanceof Student) {
            students.add(s);
        }
    }
}

Cast s to Student before adding it.

Sotirios Delimanolis
– Sotirios Delimanolis

2017-08-22 04:25:33 +00:00
Commented Aug 22, 2017 at 4:25 — Sotirios Delimanolis
– Sotirios Delimanolis, Commented Aug 22, 2017 at 4:25

OLIVER.KOO · Accepted Answer · 2017-08-22 04:27:18Z

2

ArrayList<Student> students = new ArrayList<>(); shows that students is a ArrayList that contain the Object Student.

Therefore you need to cast your s Object to Student before adding it to the students list. like such students.add((Student)s); Here is how you cast Object in Java.

answered Aug 22, 2017 at 4:27

OLIVER.KOO

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Comments

Cardinal System · Accepted Answer · 2017-08-22 05:01:11Z

0

Just to avoid any errors, change the way you construct the array list:

ArrayList<Student> students = new ArrayList<>(); 
ArrayList<Student> students = new ArrayList<Student>();

As for the add method, you want to cast to the passing object otherwise the JVM will not know that the object being passed is instanceof Student:

students.add((Student) s);

Also, you should get an IDE, they usually solve these problems before they happen.

edited Aug 22, 2017 at 5:01

answered Aug 22, 2017 at 4:26

Cardinal System

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2 Comments

Snar3 Over a year ago

Thanks! I am using Netbeans though I didn't get any warnings.

Cardinal System Over a year ago

@Snar3 netbeans is a confusing IDE in my opinion, try using Eclipse. =)

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