CODEWITHSUNDEEP
javaabstract-class
Apprentice Programmer
Apprentice Programmer

Reputation: 1515

returning a value within a abstract method

I have a abstract class called temperature with the 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 i have a Celcius and Fahrenheit class that extend from temperature, but for space sake ill show Celcius

  public class Celsius extends Temperature
   { 

      public Celsius(float t)
  {
    super(t);
  }


  public String toString()
  {
    // TODO: Complete this 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 my main program creates a new celcius object as follows

      Temperature inputTemp = null , outputTemp = null;
      inputTemp = new Celsius(temp_val);

outputTemp is then assigned to inputemp calling the toFahrenheit method

      outputTemp = inputTemp.toFahrenheit();

the resulting answer is then placed in the toString method

      outputTemp.toString

As far as i know, the Celcius constructor uses the Temperature constructor to store the passed in parameter of temp_val. However, what gets me confused is that how do i return the converted value of Celcius to Fahrenheit with inputTemp.toFahrenheit method?? I tried returning this.getValue() * 9 / 5 + 32, but eclipse complains that since getValue() is a float method, i either have to change the Overriding method to float, or change getValue() a Temperature, but both dont really work....

Upvotes: 1

Views: 5666

Answers (4)

Harry
Harry

Reputation: 1472

Why don't you change the toCelsius and toFahrenheit methods to return a float rather than a temperature?

@Override
public Float toFahrenheit() {
  // TODO Auto-generated method stub
  return (getValue() * 9.0 /5.0 +32.0 );
}

Also, does it really make sense to declare the methods toFahrenheit and toCelcius in the base class? Would you not rather declare toFahrenheit only in the Celcius class and toCelcius only in the Fahrenheit class?

Upvotes: 0

Balayesu Chilakalapudi
Balayesu Chilakalapudi

Reputation: 1406

In the toFahrenheit() you need to return the current object of type Temperature like this,

@Override
public Temperature toFahrenheit() {
  // TODO Auto-generated method stub
  return this;

}

you can get the converted resultant value like this, 

Temperature inputTemp = null , outputTemp = null;
inputTemp = new Celsius(temp_val);

outputTemp = inputTemp.toFahrenheit();

float result=outputTemp.getValue();

Upvotes: 0

Jean Logeart
Jean Logeart

Reputation: 53829

In Celsius, toCelsuis should return this because the Temperature is already in celsius. The toFahrenheit method should return a new Fahrenheit instance :

@Override
public Temperature toCelsius() {
    return this;
}

@Override
public Temperature toFahrenheit() {
    return new Fahrenheit(this.getValue() * 9D / 5D + 32D);
}

And the other way around for the Fahrenheit class.

Upvotes: 3

Pablo Francisco Pérez Hidalgo
Pablo Francisco Pérez Hidalgo

Reputation: 27702

toFahrenheit returns a reference to Temperature.

You have only two concrete classes matching that return value: Celsius and Fahrenheit so you should return a new object of one of these classes. Presumably Fahrenheit is it seems to be the aim of your method so, for Celsius class, you should have something like:

@Override
  public Temperature toFahrenheit() {
    return new Fahrenheit( this.getValue() * 9.0 /5.0 +32.0 );
  }

And, as your class is already representing temperature in celsius:

@Override
 public Temperature toCelsius() {
   return this;
 }

Upvotes: 1

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