[SOLVED] Cant figure out null pointer exception

[todd2230]

Hey guys im fairly new to java. I've been trying to figure out why i'm getting this null pointer exception at runtime with no luck. Any advice would be much appreciated.

Code:

import java.io.*;

public class MyData {
	public static void main(String[] args) {
		//Student aStudent = new Student();
		Student bStudent = new Student("1234567","John", "12 Wick St Redwood","2344","08/08/1986","95066713");
		bStudent.printStudent();
		}
}

class Student{
   private String number;
   private String name;
   //private boolean male;
   private String address;
   private int post;
   private Date dob; // not yet instantiated
   private String phone;
   //private double marks[] = null;
   
   Student(){ // default constructor
		System.out.println("Student Created");
   }
   
   Student(String number, String name, String address, String post, String dobString, String phone){ // constructor
   this.number = number;
   this.name = name;
   this.address = address;
   this.post = Integer.parseInt(post); // convert string to int.
   Date dob = new Date(dobString); // intialize dob object
   this.phone = phone;
   dob.printDob();
   }
   
   void printStudent(){
	System.out.println(number);
	System.out.println(name);
	System.out.println(address);
	System.out.println(post);
	dob.printDob(); //ERROR HERE
	System.out.println(phone);
   }
   
}

class Date{
	int day, month, year;
	
	Date(){ // default constructor
	day = 0;
	month = 0;
	year = 0;
	}
	
	Date(String dobString){
	String input[] = new String[10]; // for storing day month year
	String patternStr = "/"; // character to split line at.
	input = dobString.split(patternStr);
	day = Integer.parseInt(input[0]); // convert string to int.
	month = Integer.parseInt(input[1]);
	year = Integer.parseInt(input[2]);
	
	}
	
	void printDob(){ // to print out date of birth
		System.out.println(day + "/" + month + "/" + year); //format dd/mm/yyyy
	}
	
}

[Zosden]

you never called something new and whatever its name.

[sanjeevtarar]

Hello,

See the code, It is explained on line number 32 and 42

Code:

import java.io.*;

public class MyData {
	public static void main(String[] args) {
		//Student aStudent = new Student();
		Student bStudent = new Student("1234567","John", "12 Wick St Redwood","2344","08/08/1986","95066713");
		bStudent.printStudent();
		}
}

class Student{
   private String number;
   private String name;
   //private boolean male;
   private String address;
   private int post;
   private Date dob; // not yet instantiated
   private String phone;
   //private double marks[] = null;
   
   Student(){ // default constructor
		System.out.println("Student Created");
   }
   
   Student(String number, String name, String address, String post, String dobString, String phone){ // constructor
   this.number = number;
   this.name = name;
   this.address = address;
   this.post = Integer.parseInt(post); // convert string to int.
   Date dob = new Date(dobString); // intialize dob object
   this.phone = phone;
   dob.printDob(); // Here You are not getting error because you are using 
   //Date object that is initialized at line 30
   // If you put this, you will not get any error
   this.dob = dob;
   }
   
   void printStudent(){
	System.out.println(number);
	System.out.println(name);
	System.out.println(address);
	System.out.println(post);
	dob.printDob(); // Here dob object is null, because in this case 
        //the dob Object is referencing to Object that defined on
	// line number 17 and is not initiantiated. It is NULL.
	System.out.println(phone);
   }
   
}

class Date{
	int day, month, year;
	
	Date(){ // default constructor
	day = 0;
	month = 0;
	year = 0;
	}
	
	Date(String dobString){
	String input[] = new String[10]; // for storing day month year
	String patternStr = "/"; // character to split line at.
	input = dobString.split(patternStr);
	day = Integer.parseInt(input[0]); // convert string to int.
	month = Integer.parseInt(input[1]);
	year = Integer.parseInt(input[2]);
	
	}
	
	void printDob(){ // to print out date of birth
		System.out.println(day + "/" + month + "/" + year); //format dd/mm/yyyy
	}
	
}

[todd2230]

Thanks for the advice guys, got it workin now!!

[sanjeevtarar]

Quote:

Originally Posted by todd2230

Thanks for the advice guys, got it workin now!!

Ok.. mark your thread SOLVED

[todd2230]

And done, thanks again!

[sukatoa]

Quote:

Originally Posted by todd2230

And done, thanks again!

Don't forget to add reputation to those who helped/answers your problem.