Java: how to pass arguments into constructor? Undefined method error?

Question

Ok, so I'm in need of some basic help. Here's the tutorial I'm trying to learn from (http://docs.oracle.com/javase/tutorial/java/javaOO/classes.html), but I'm confused as to how to actually pass data into it. The problem is I've got my Pascal brain on when trying to learn java...

Here's my code. What am I doing wrong?

public class OrigClass{
    public static void main(String[] args){
        StudentData(17, "Jack"); //error here: the method StudentData(int, String) is undefined for the type OrigClass
    }

    public class Student{
        public void StudentData(int age, String name){
            int sAge = age;
            String sName = name;
            System.out.println("Student Name: " + sName + " | Student Age: " + sAge);
        }
    }
}

Thanks in advance for the help :)

Sergey Kalinichenko · Accepted Answer · 2013-07-24 15:54:42Z

5

Constructor is not just a method: you need to give it the same name as the class, and call it with a new operator, like this:

public class Student{
    // Declare the fields that you plan to assign in the constructor
    private int sAge;
    private String sName;
    // No return type, same name as the class
    public Student(int age, String name) {
        // Assignments should not re-declare the fields
        sAge = age;
        sName = name;
        System.out.println("Student Name: " + sName + " | Student Age: " + sAge);
    }
}
// This goes in the main()
Student sd = new Student(17, "Jack");

answered Jul 24, 2013 at 15:54

Sergey Kalinichenko

729k85 gold badges1.2k silver badges1.6k bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

amicngh Over a year ago

He has StudentData as method not Student might be his understanding to call the method is wrong.

Sergey Kalinichenko Over a year ago

@amicngh Right - that's one of the things that's wrong with his alleged "constructor" :-)

mcfinnigan · Accepted Answer · 2013-07-24 15:56:19Z

2

There are several issues in your code.

Firstly, you've defined the constructor of StudentData like a normal method - constructors have no return type.

Secondly, you need use the new keyword to create a non-primitive object in Java.

public class OrigClass{
    public static void main(String[] args){
        new Student(17, "Jack"); 
    }
}

public class Student{
   public Student(int age, String name){
       int sAge = age;
       String sName = name;
       System.out.println("Student Name: " + sName + " | Student Age: " + sAge);
   }
}

answered Jul 24, 2013 at 15:56

mcfinnigan

11.7k38 silver badges28 bronze badges

9 Comments

Sergey Kalinichenko Over a year ago

OP also forgot to declare the fields, assigning constructor args to local variables inside the constructor.

mcfinnigan Over a year ago

That in and of itself won't prevent his code from compiling and executing, it just means that his results will be nonsensical :)

Jonathan Over a year ago

Note that Student is an inner class of OrigClass so you would have to do (new OrigClass()).new Student(17, "Jack") in order to instantiate a Student.

amicngh Over a year ago

@dasblinkenlight. My understanding is StudentData is method rather than assuming this Student construtor.

Jonathan Over a year ago

@mcfinnigan np, it wasn't obvious to me until I reformatted the code. Although I would suggest your solution over the nested class approach.

|

amicngh · Accepted Answer · 2013-07-24 17:21:33Z

2

If I am assuming you have written Student class correctly without considering Java naming convention in mind and StudentData is method then the way to call method StudentData is incorrect.First create object ofStudent class and then call the method

Update: Considering Student is inner class

 public static void main(String[] args){
    new OrigClass().new Student().StudentData(17, "Jack");// Considering Student is inner class
  }

edited Jul 24, 2013 at 17:21

answered Jul 24, 2013 at 15:56

amicngh

7,9293 gold badges37 silver badges55 bronze badges

2 Comments

Steve Kuo Over a year ago

Speaking of convention, Java is a word and not an acronym, and thus should not be written in all uppercase.

amicngh Over a year ago

@SteveKuo seconded :).

Mat · Accepted Answer · 2013-08-30 15:41:41Z

1

public class OrigClass {

    public static void main(String[] args) {
        Student obj = new Student();
        obj.studentData(17, "Jack");

    }
}

public class Student {   

    public void studentData(int sName, String sAge) {
        System.out.println("Student Name: " + sName + " | Student Age: " + sAge);
    }
}

edited Aug 30, 2013 at 15:41

Mat

208k41 gold badges408 silver badges423 bronze badges

answered Jul 24, 2013 at 16:05

Dereje Goshu

1991 gold badge1 silver badge6 bronze badges

Comments

Prashant_Sharma · Accepted Answer · 2018-06-29 20:28:26Z

so, first of all, you can't access a non-static member(StudentData(int age, String name)) from within a static method(public static void main(String[] args)). So if you want to access the method from within your static main method you would need to do the following:

Create an alternate method(for eg: name it xyz()), that will create an object(eg: std) for your inner class Student and then calls the StudentData method with the syntax std.StudentData(17,"JACK");.
Next thing call this alternate method from the static main method by creating an object (eg: obj) of the outer class and invoking the alternate method with the help of this obj like obj.alternateMethodName();

Here's the complete code showing how you can achieve the desired output:

public class OrigClass{
public static void main(String[] args){
    OrigClass obj= new OrigClass();
    obj.getStudentData();
}
public void getStudentData(){
    Student std = new Student();
    std.StudentData(17, "Jack");
}

public class Student{
    public void StudentData(int age, String name){
        int sAge = age;
        String sName = name;
        System.out.println("Student Name: " + sName + " | Student Age: " + sAge);
    }
}

}

Collectives™ on Stack Overflow

Java: how to pass arguments into constructor? Undefined method error?

5 Answers 5

2 Comments

9 Comments

2 Comments

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

5 Answers 5

2 Comments

9 Comments

2 Comments

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related