Logic error possibly misunderstanding in java assignment -

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i've been having numerous problems getting project work correctly i'm stuck on getting class work properly. whats suppose take current station radio class , pass along class. problem i'm trying select between , fm every time run it, displays station. don't understand why automatically gets set station. 

public class autoradiosystem {   private radio selectedradio;   private amradio radioam;   private fmradio radiofm;    private xmradio radioxm;    //is correct place initialize these?    radio amradio = new amradio();   radio fmradio = new fmradio();   public autoradiosystem()   {    //even making selected radio fm still produces values    selectedradio = radiofm;   }    // problem lies , more. shouldn't return 0.0 without station being selected.     public double getcurrentstation()   {     if (selectedradio == radioam)     {       return amradio.getcurrentstaion();     }     else if (selectedradio == radiofm)     {       return fmradio.getcurrentstaion();     }     return 0.0;   }    //i'm not sure if i'm setting correctly switch radio fm    public void selectradio()   {     if (selectedradio == radioam)       selectedradio = radiofm;   }   public static void main (string [] args) {      autoradiosystem c = new autoradiosystem();     c.selectradio();     double b = c.getcurrentstation();     system.out.println(b);   } }  public class amradio extends radio {   private static final double max_station = 1605;   private static final double min_station = 535;   private static final double increment = 10;   public amradio()   {     currentstation = min_station;   }   public  double getmax_station()   {     return this.max_station;   }   public  double getmin_station()   {     return this.min_station;   }   public  double getincrement()   {     return this.increment;   }   public string tostring()   {     string message = ("am " + this.currentstation);     return message;   }  }  public class fmradio extends radio {   private static final double max_station = 108.0;   private static final double min_station = 88.0;   private static final double increment = .01;   public fmradio()   {     currentstation = min_station;   }   public  double getmax_station()   {     return this.max_station;   }   public  double getmin_station()   {     return this.min_station;   }   public  double getincrement()   {     return this.increment;   }   public string tostring()   {     string message = ("fm " + this.currentstation);     return message;   }  }   public abstract class radio {  double currentstation;   radioselectionbar radioselectionbar;  public radio()  {   }  public abstract double getmax_station();  public abstract double getmin_station();  public abstract double getincrement();  public void up()  {   }  public void down()  {   }  public double getcurrentstaion()  {    return this.currentstation;  }  public void setcurrentstation(double freq)  {    this.currentstation = freq;  }  public void setstation(int buttonnumber, double station)  {  }  public double getstation(int buttonnumber)  {    return 0.0;  }  public string tostring()   {     string message = ("" + currentstation);     return message;   }   }

the problem is, in .getcurrentstation(), both selectedradio & radioam not init , null.

the mistake begin with:

public void selectradio() {     if (selectedradio == radioam)     {         selectedradio = radiofm;     } }

here, selectedradio = null, it's never assign value.

edit: believe you're begin this, little more details help.

  1. you make mistake when declare 2 field, amradio & radioam init 1 of them , use another.
  2. you didn't set value selectedradio , compare it, return false
  3. the best place init value instance constructor method, here autoradiosystem()

you may want change code this:

private radio selectedradio; public autoradiosystem() {     selectedradio = new fmradio(); } // compare, using instanceof, better design use enum value instead,

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