简单的Java程序错误

Question

I'm a Java beginner, and here's my issue : I don't understand why my output is "null" while implemanting my Print program. As I understand my code, it is supposed to display :" http://www.google.com ". I tried with a StringBuilder, and I still have this problem. Could someone give me some help please ? Thanks

URL.java :

public class URL {

    String url;

    public void create(){
        url = new String();
        url+=("http://www.google.com");
    }

    public String geturl() {
         return this.url;
    } 

}

Print.java :

public class Print {

public static  void main(String[] args) throws Exception {
URL link = new URL();   
System.out.print(link.geturl());
}

}

Answer 1

You need to call link.create() , or change the create() function to be a constructor instead. Like this:

public URL(){
    url = new String();
    url+=("http://www.google.com");
}

Answer 2

An even better approach is to initialize the url instance variable within a constructor. By doing that the url instance variable will automatically be initialize when you create an instance of URL class and you eliminate the need for the create method.

 public class URL{
     private String url;

     //Constructor
     public URL (){
        url = "http://www.google.com";
     }

     public String getUrl (){
        return url;
     }

 }

 public class Print{
      public static void main (String[] args){
         URL url = new URL ();
         System.out.println (url.getUrl());

      }
 }