Reputation:

Java: How to properly return result using a method

I writing a program that will print "Based on the temperature it is likely" season A, B, C, or D by calling a method.

Code :

import java.util.Scanner;
import javax.swing.*;

public class Seasons {

  public static void main(String[] args) {
    int inputTemp;
    String response = JOptionPane.showInputDialog(null,
            "Enter the temperature");
    inputTemp = Integer.parseInt(response);
    String message = "Based on the temperature of " + inputTemp
            + " it is most likely " + determineSeason(inputTemp);
    JOptionPane.showMessageDialog(null, message);

  }

  public static String determineSeason(int inputTemp) {
    String season = null;
    if (inputTemp > 130 || inputTemp < -20) { 
        JOptionPane.showMessageDialog(null,"Invalid");
    }

    else if (inputTemp >= 90) {
        JOptionPane.showMessageDialog(null,"summer"); }

    else if (inputTemp >= 70 && inputTemp < 90) {
        JOptionPane.showMessageDialog(null,"spring"); }
    else { 
        JOptionPane.showMessageDialog(null,"winter"); }

    return season; 
  }
}

The program is returning with a JOptionPane the season from my method, then presents the JOptionPane from main method where I need it to say "Based on the temperature the season is Season A, B, C, or D.

Any advice on what I'm missing would be appreciated!

Upvotes: 0

Answers (3)

J.Adler

Reputation: 1463

I would advise you to use interfaces and java 8 Streams. That way you avoid a lot of ifs, which makes the code less verbose, and the introduction of a new class becomes trivial.

Even in small or simple projects, consider interface-oriented programming, which makes you think more before declaring a new method.

Season.java

public abstract class Season {

    public <T extends Season> Stream season(Integer temperature) {
        if (temperature <= max() && temperature >= min()) {
            return Stream.of(this);
        }
        return Stream.empty();
    }

    public abstract Integer max();

    public abstract Integer min();

    @Override
    public abstract String toString();
}

Summer.java

public class Summer extends Season {

    @Override
    public String toString() {
        return "Summer";
    }

    @Override
    public Integer max() {
        return 90;
    }

    @Override
    public Integer min() {
        return 70;
    }
}

Spring.java

public class Spring extends Season {

    @Override
    public String toString() {
        return "Spring";
    }

    @Override
    public Integer max() {
        return 69;
    }

    @Override
    public Integer min() {
        return 40;
    }
}

Main.java

public class Main {

    public static void main(String[] args) {

        Collection<Season> seasons = new ArrayList();
        seasons.add(new Summer());
        seasons.add(new Winter());
        seasons.add(new Season() {
            @Override
            public Integer max() {
                return 39;
            }

            @Override
            public Integer min() {
                return 10;
            }

            @Override
            public String toString() {
                return "Winter";
            }
        });

        String response = JOptionPane.showInputDialog(null, "Enter the temperature");
        int temperature = Integer.parseInt(response);
        String msg = "Based on the temperature of %d it is most likely %s%n";

        seasons.stream().forEach(s -> {
            s.season(temperature).findAny().ifPresent(t -> {
                String message = String.format(msg, temperature, t);
                JOptionPane.showMessageDialog(null, message);
            });
        });
    }
}

Upvotes: 0

Andrew

Reputation: 49606

determineSeason should be a private method that doesn't deal with UI parts (doesn't interact with Swing components).

private String determineSeason(int inputTemp) {
    if (inputTemp > 130 || inputTemp < -20) { 
        throw new IllegalArgumentException("Invalid");
    }

    if (inputTemp >= 90) {
        return "summer";
    } else if (inputTemp >= 70 && inputTemp < 90) {
        return "spring";
    } else { 
        return "winter";
    }
}

season can't be "Invalid", you aren't going to display "it is most likely Invalid", so it's better to throw an exception from the method, catch it on the caller side and show an error message window:

class Seasons {

    public static void main(String[] args) {
        String response = JOptionPane.showInputDialog(null, "Enter the temperature");
        int inputTemp = Integer.parseInt(response);
        try {
            String message = String.format("Based on the temperature of %d, it is most likely %s", inputTemp, determineSeason(inputTemp));
            JOptionPane.showMessageDialog(null, message);
        } catch (IllegalTemperatureValueException | NumberFormatException e) {
            JOptionPane.showMessageDialog(null, e.getMessage(), "Error", JOptionPane.ERROR_MESSAGE);
        }

    }

    private static String determineSeason(int inputTemp) throws IllegalTemperatureValueException {
        if (inputTemp > 130 || inputTemp < -20) {
            throw new IllegalTemperatureValueException("incorrect temperature value");
        }

        return inputTemp >= 90 ? "summer" : (inputTemp >= 70 ? "spring" : "winter");
    }
}

class IllegalTemperatureValueException extends Exception {
    public IllegalTemperatureValueException(String message) {
        super(message);
    }
}

Upvotes: 1

Makoto

Reputation: 106390

You don't assign a result to season and you just return null.

Change each conditional inside of your if statement to something along the lines of this.

String season = null;
if (inputTemp > 130 || inputTemp < -20) {
    season = "invalid";
} else if(inputTemp >= 90) {
    season = "summer";
}