java - returning a value within a abstract method -

i have abstract class called temperature following

 public abstract class temperature  {       private float value; public temperature(float v) {     value = v; }  public final float getvalue() {     return value; }  public abstract temperature tocelsius(); public abstract temperature tofahrenheit(); } 

then have celcius , fahrenheit class extend temperature, space sake ill show celcius

  public class celsius extends temperature    {         public celsius(float t)   {     super(t);   }     public string tostring()   {     // todo: complete method     return "";   }     @override   public temperature tocelsius() {     // todo auto-generated method stub     return null;   }     @override   public temperature tofahrenheit() {     // todo auto-generated method stub     return null;   }       } 

so main program creates new celcius object follows

      temperature inputtemp = null , outputtemp = null;       inputtemp = new celsius(temp_val); 

outputtemp assigned inputemp calling tofahrenheit method

      outputtemp = inputtemp.tofahrenheit(); 

the resulting answer placed in tostring method

      outputtemp.tostring 

as far know, celcius constructor uses temperature constructor store passed in parameter of temp_val. however, gets me confused how return converted value of celcius fahrenheit inputtemp.tofahrenheit method?? tried returning this.getvalue() * 9 / 5 + 32, eclipse complains since getvalue() float method, either have change overriding method float, or change getvalue() temperature, both dont work....

in celsius, tocelsuis should return this because temperature in celsius. tofahrenheit method should return new fahrenheit instance :

@override public temperature tocelsius() {     return this; }  @override public temperature tofahrenheit() {     return new fahrenheit(this.getvalue() * 9d / 5d + 32d); } 

and other way around fahrenheit class.