Problem with "extends" ,why my code print null on the console?

Question

two classes work together.
//Super class is :
public class Father
     public String data = "father";
     Father()
          printData();
     public void printData()
          System.out.println("fatherprint->"+data);
//it's Son class is :
public class Son extends Father
     Son()
     String db = new String("son");//in the printData method ,it print null.
//here, if it define like this: static String db = new String("son");
//then the output works well.
     public void printData()
          System.out.println("output ->"+this.db);
     public static void main(String[] args)
          Son son = new Son();
when i run the Son.java ,it just print "output ->null"?why is so?
hoping for your tips.

Answer 1

Because the superconstructor Father() is run before the fields in Son are initialized. The superconstructor calls the overridden method printData() in Son. Only after the superconstructor is run do the fields in Son get initialized.
Also, there's no reason to say = new String("..."), you can just use = "..."