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package eu.equalparts.cardbase.comparator;
import java.lang.annotation.Annotation;
import java.lang.reflect.Field;
import java.lang.reflect.ParameterizedType;
import java.lang.reflect.Type;
import java.util.Comparator;
import java.util.function.BiFunction;
import eu.equalparts.cardbase.cards.Card;
import eu.equalparts.cardbase.comparator.SpecialFields.DirtyNumber;
import eu.equalparts.cardbase.comparator.SpecialFields.Rarity;
/**
* I'm new to this reflection business, so bear with me.
* <br><br>
* The idea here is to avoid having to write one class
* for each comparable field in {@code Card}. The program
* can dynamically instantiate them as cards are compared
* by different fields.
* <br><br>
* This class uses reflection to determine if the specified
* field is comparable with itself upon construction, and throws
* an {@code IllegalArgumentException} if that is not the case.
*
* @author Eduardo Pedroni
*
*/
@SuppressWarnings({"rawtypes", "unchecked"})
public class CardComparator implements Comparator<Card> {
/**
* The field being compared.
*/
private Field fieldToCompare;
/**
* The comparison delegate to use for the specified field.
*/
private BiFunction<Comparable, Comparable, Integer> comparisonDelegate = (field1, field2) -> field1.compareTo(field2);
/**
* Creates a new comparator for the specified field only. This class
* will only be constructed successfully if the field comes from
* {@code Card} and can be compared to itself (i.e. implements
* {@code Comparable<T>} where T is its own type.
* <br>
* For reference, {@code String} and {@code Integer} are both self comparable.
*
* @param fieldToCompare the field this comparator will use to compare cards, as declared in {@code Card}.
*/
public CardComparator(Field fieldToCompare) {
if (fieldToCompare.getDeclaringClass().equals(Card.class) &&
isSelfComparable(fieldToCompare.getType())) {
this.fieldToCompare = fieldToCompare;
// if annotated with a special comparator, set the comparison delegate here
for (Annotation annotation : fieldToCompare.getAnnotations()) {
if (annotation.annotationType() == DirtyNumber.class) {
this.comparisonDelegate = ComparatorDelegates::compareDirtyNumber;
} else if (annotation.annotationType() == Rarity.class) {
this.comparisonDelegate = ComparatorDelegates::compareRarity;
}
}
} else {
throw new IllegalArgumentException("The field provided is not valid.");
}
}
@Override
public int compare(Card o1, Card o2) {
/*
* we've already checked that the field is self comparable,
* so we are now free to cast to comparable
*/
try {
Comparable field1 = (Comparable) fieldToCompare.get(o1);
Comparable field2 = (Comparable) fieldToCompare.get(o2);
// if either or both fields' values are null, skip delegation altogether since delegates are not required to deal with null values
if (field1 == null) {
if (field2 == null) {
return 0;
} else {
return -1;
}
} else if (field2 == null) {
return 1;
} else {
return comparisonDelegate.apply(field1, field2);
}
} catch (IllegalArgumentException e) {
System.out.println("Error: class Card does not define field \"" + fieldToCompare.getName() + "\".");
e.printStackTrace();
} catch (IllegalAccessException e) {
System.out.println("Error: field " + fieldToCompare.getName() + " in Card is not visible.");
e.printStackTrace();
}
// fallback, this shouldn't happen
return 0;
}
/**
* Use reflection to determine if the specified class can be compared with itself.
*
* @param type the type to analyse.
* @return true if the type can be compared to itself using {@code compareTo()}, false otherwise.
*/
private boolean isSelfComparable(Class<?> type) {
// go through all interfaces implemented by this class
for (Type implementedInterface : type.getGenericInterfaces()) {
// check if any parameterised interface found is "Comparable"
if (implementedInterface instanceof ParameterizedType) {
ParameterizedType genericInterface = (ParameterizedType) implementedInterface;
if (genericInterface.getRawType().equals(Comparable.class)) {
// check that the type argument of comparable is the same as the field type itself
return genericInterface.getActualTypeArguments()[0].equals(type);
}
}
}
return false;
}
}
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