A Groovy temperature conversion with Categories

AncientTemperature.java

package com.asoftwareguy.temperature;

/**
 * This is an "old" existing Java class representing temperature.
 * It assumes the unit is Fahrenheit.
 *
 */
public final class AncientTemperature {
	
	// in degrees Fahrenheit
	private int temp;
	
	public AncientTemperature(int temp) {
		this.temp = temp;
	}

	@Override
	public String toString() {
		return new StringBuilder().append("The current temperature is " + temp + " degrees F.").toString();
	}
}

TemperatureConversion.groovy

package com.asoftwareguy.temperature

class TemperatureConversion {

	static AncientTemperature getFahrenheit(String fahrenheit) {
		new AncientTemperature(fahrenheit as int)
	}

	static AncientTemperature getCelsius(String celsius) {
		BigDecimal fahrenheit = (celsius.toInteger() *  (9/5) + 32)
		fahrenheit = fahrenheit.setScale(0, BigDecimal.ROUND_DOWN)
		new AncientTemperature(fahrenheit.toString() as int)
	}
	
	static AncientTemperature getFahrenheit(Integer fareheit) {
		new AncientTemperature(fareheit)
	}

	static AncientTemperature getCelsius(Integer celsius) {
		BigDecimal fahrenheit = (celsius *  (9/5) + 32)
		fahrenheit = fahrenheit.setScale(0, BigDecimal.ROUND_DOWN)
		new AncientTemperature(fahrenheit.toString() as int)
	}
	
	static AncientTemperature plus(AncientTemperature first, AncientTemperature second) {
		int tempFirst = first.temp
		int tempSecond = second.temp;
		int newTemp = tempFirst + tempSecond
		return new AncientTemperature(newTemp)
	}
	
	static AncientTemperature minus(AncientTemperature first, AncientTemperature second) {
		int tempFirst = first.temp
		int tempSecond = second.temp;
		int newTemp = tempFirst - tempSecond
		return new AncientTemperature(newTemp)
	}
}

TemperatureTest.groovy

package com.asoftwareguy.temperature

use(TemperatureConversion) {
	assert  "100".fahrenheit.toString() == 'The current temperature is 100 degrees F.'
	println "100".fahrenheit
	
	assert 	"50".fahrenheit.toString() == 'The current temperature is 50 degrees F.'
	println "50".fahrenheit
	
	assert 	"32".fahrenheit.toString() == 'The current temperature is 32 degrees F.'
	println "32".fahrenheit
	
	assert 	"100".celsius.toString() == 'The current temperature is 212 degrees F.'
	println "100".celsius
	
	assert 	100.fahrenheit.toString() == 'The current temperature is 100 degrees F.'
	println 100.fahrenheit
	
	assert 	50.fahrenheit.toString() == 'The current temperature is 50 degrees F.'
	println 50.fahrenheit
	
	assert 	32.fahrenheit.toString() == 'The current temperature is 32 degrees F.'
	println 32.fahrenheit
	
	assert 	100.celsius.toString() == 'The current temperature is 212 degrees F.'
	println 100.celsius
	
	assert (100.fahrenheit + 50.fahrenheit).toString() == 'The current temperature is 150 degrees F.'
	println 100.fahrenheit + 50.fahrenheit
	
	assert (100.fahrenheit + 0.celsius).toString() == 'The current temperature is 132 degrees F.'
	println 100.fahrenheit + 0.celsius
	
	assert (100.fahrenheit - 0.celsius).toString() == 'The current temperature is 68 degrees F.'
	println 100.fahrenheit - 0.celsius
}