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();


}

} 

Answer 1

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.