how to use array list to access methods of access list type object in java

Question

in my program there are three class Student,School and TestStudent. I have declared students state inside student class and also there are methods for getting students subject,i have created an array list of type student in School class,but when i try to access student's method in school i get error newStudent type can not be resolved.Here are my codes.

public class Student {
        String name;
    String subject;
    int age;
    Student(String name,String subject,int age){
    this.name = name;
    this.subject = subject;
    this.age = age;
}
public void setName(String name){
    this.name = name;
}
public String getName(){
    return this.name;
}
public String getSubject(){
    return this.subject;
}
public int getAge(){
    return this.age;
}

}

public class School {
public ArrayList <Student> students = new ArrayList <Student>(); 
public void addStudent(String name,String subject,int age){
    Student newStudent = new Student(name,subject,age);
    students.add(newStudent);
}
public void showSubject(String student){
     newStudent.getSubject();


}

}

changed the code using rohit's suggestion.now its working.

Ankit Mishra
– Ankit Mishra

2013-01-06 10:37:17 +00:00
Commented Jan 6, 2013 at 10:37 — Ankit Mishra
– Ankit Mishra, Commented Jan 6, 2013 at 10:37

Community · Accepted Answer · 2017-05-23 11:43:07Z

4

newStudent.getSubject();

This is not what you want. Because you haven't retrieved that student yet from the ArrayList.

You would need to iterate over the ArrayList, and see which student have the name as passed in parameter. So, just use a for-each loop to iterate over your ArrayList, and return appropriate Student.

So, your method should look like: -

public void showSubject(String student){
     for (Student student: students) {
        if (student.getName().equals(student)) {
            System.out.println(student.getSubject());
        }
     }
}

Note that, using a Map here would be a better idea as explained by @Peter in his answer.

edited May 23, 2017 at 11:43

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answered Jan 6, 2013 at 10:21

Rohit Jain

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Comments

Peter Lawrey · Accepted Answer · 2013-01-06 10:23:46Z

2

If you want to look up a student by name, I would make the name of a student immutable and use a Map<String, Student> instead. This would allow you to write

 Student student = map.get(studentName);

Using a List, you would have to search through every entry as Rohit suggests. Note: it is possible to have multiple students with the same name (as in real life) with a List.

answered Jan 6, 2013 at 10:23

Peter Lawrey

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2 Comments

Rohit Jain Over a year ago

Umm. Why have you explicitly specified making name of the student immutable? Since it's a String, it is implicit.

Peter Lawrey Over a year ago

The Student name; should be final so it can be safely used as a key.

TJ- · Accepted Answer · 2013-01-06 10:21:24Z

1

newStudent is a local variable in addStudent(), hence you cannot access it from showSubject().

I don't know what should be your logic of accessing the subject, but, for example, it could be accessed via students.get(0).getSubject() [provided the list is not empty]

answered Jan 6, 2013 at 10:21

TJ-

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