String passed as argument to a constructor returns null value

[eLancaster]

I made a program to practice inheritance which uses a GUI.
It consists of three classes for the moment:

School_School.java

abstract public class School_School 
{
	public abstract void getName();
	public abstract void printName();
}

School_Teachers.java

import javax.swing.JOptionPane;

public class School_Teachers extends School_School{
	private String firstName;
	private String lastName;
	private String name = firstName + " " + lastName;
	public School_Teachers(String firstName,String lastName)
	{
		this.firstName=firstName;
		this.lastName=lastName;
	}
	public School_Teachers()
	{
		getName();
	}
	public void getName()
	{
		this.firstName = JOptionPane.showInputDialog(null, "Enter First Name: ", "Teacher | Registration", JOptionPane.OK_OPTION);
		this.lastName = JOptionPane.showInputDialog(null, "Enter Last Name: ", "Teacher | Registration", JOptionPane.OK_OPTION);
	}
	public void printName()
	{
		System.out.println("Name Entered: "+this.name);
	}
}

School_MainClass.java

public class School_MainClass {
	public static void main(String[] args) {
		School_School teacher = new School_Teachers("Severus","Snape");
		teacher.printName();

	}

}

The problem is that the output returns
Name entered: null null
and i dont understand why that is? Could someone please explain and tell me where i've gone wrong - thanks!

[JosAH]

import javax.swing.JOptionPane;

public class School_Teachers extends School_School{
	private String firstName;
	private String lastName;
	private String name = firstName + " " + lastName;
	public School_Teachers(String firstName,String lastName)
	{
		this.firstName=firstName;
		this.lastName=lastName;
	}

You don't initialize firstName and lastName (you can't because those names are only known when the constructor is called) so they equal null. You try to initialize the name member with those other two null values. Set the value of your name value in your constructor (after firstName and lastName have received they value) and you'r fine.

kind regards,

Jos