ArrayList get() method to find class variable?

Question

So I have a list of a class type. For example, I have a ClassRoom class and a Student class.

I created an ArrayList of Students: ArrayList<Student> studList = new ArrayList<>();

I have a method to add a student, so index 0 is occupied:

    public void addStudent(int studID, String studName, int studPhoneNum){
        Student stud = new Student(studName, studID, studPhoneNum);
        studList.add(stud);
        System.out.println(studList);
    }

Now what I want is to search for a specific value inside the student's variables. So for example, a student is represented by a name, ID and phone number. How do I loop over that Student list to find a student with a specific phone number, then print him or his phone number?

This is the function:

    public void sendMessage(int phone){
        for (Student s : studList) {
            studList.get(studPhoneNum);
            \\ then print the Student the phone number belongs to..
        }
    }

I do have a studPhoneNum variable set in the Student class.

if(s.getPhonenumber == phone)

Murat Karagöz
– Murat Karagöz

2020-01-13 09:22:44 +00:00
Commented Jan 13, 2020 at 9:22 — Murat Karagöz
– Murat Karagöz, Commented Jan 13, 2020 at 9:22
Thank you! I can't believe I didn't find this earlier.

Daniel
– Daniel

2020-01-13 09:30:39 +00:00
Commented Jan 13, 2020 at 9:30 — Daniel
– Daniel, Commented Jan 13, 2020 at 9:30

Gamopo · Accepted Answer · 2020-01-13 09:30:53Z

1

The easiest way would be to create a function to get the phone number like this:

public int getPhoneNumber(int stuID){
    for (Student s: studList) {
        if(s.id == stuID){
            return s.phoneNumber;
        }
    }
    return 0;
}

I'm supposing here that stuList is a global variable since you can access to it in addStudent without passing it as an argument, otherwise you'll have to pass it to the function. I hope it helps.

answered Jan 13, 2020 at 9:30

Gamopo

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1 Comment

Daniel Over a year ago

Thank you, I was missing the whole s.something thing. This works perfectly :)

Mark Rotteveel · Accepted Answer · 2020-01-13 13:41:38Z

1

You can do as below:

Using Java 8 stream:

studList.stream()
        .filter(student -> student.getStudPhoneNum==studPhone)
        .findFirst()
        .ifPresent(student -> {
            // Do something
        });

Using for loop:

for(Student s: studList){
    if(s.getStudPhoneNum==studPhone){
        //do something
    }
}

edited Jan 13, 2020 at 13:41

Mark Rotteveel

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answered Jan 13, 2020 at 9:35

Ankur Gupta

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Comments

Mark Rotteveel · Accepted Answer · 2020-01-13 13:42:01Z

1

Since you are iterating over studList, 's' represents every individual student in that list.

public void sendMessage(int phone){
    for (Student s : studList) {
        if (s.getStudPhoneNum() == phone){
             System.out.print(s.getStudName());
        }
    }
}

Here you would need to create getter methods (getStudPhoneNumber(), getStudName())to refer attributes of the Student class.

edited Jan 13, 2020 at 13:42

Mark Rotteveel

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answered Jan 13, 2020 at 9:31

Vishakha Lall

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