package vererbungUndGenerizitaet.relationen;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Map;
import java.util.Set;
public class BinaryRelation<T, U> {
private Map<T, Set<U>> relatedTo = new HashMap<T, Set<U>>();
public BinaryRelation() {
}
public void add(T x, U y) {
Set<U> relations = relatedTo.get(x);
// if there is no relation for left element yet
if (relations == null) {
relations = new HashSet<U>();
relatedTo.put(x, relations);
}
relations.add(y);
}
public Set<U> getRelations(T x) {
Set<U> relations = relatedTo.get(x);
return java.util.Collections
.unmodifiableSet(relations == null ? new HashSet<U>()
: relations);
}
public Set<T> getElements() {
return relatedTo.keySet();
}
public boolean isRelated(T x, U y) {
return getRelations(x).contains(y);
}
@Override
public String toString() {
StringBuilder build = new StringBuilder();
build.append("[");
for (T x : getElements()) {
for (U y : getRelations(x)) {
build.append("(");
build.append(x);
build.append(", ");
build.append(y);
build.append("),");
}
}
if (build.length() > 1)
build.replace(build.length() - 1, build.length(), "");
build.append("]");
return build.toString();
}
public static void main(String[] args) {
BinaryRelation<String, Integer> rel = new BinaryRelation<String, Integer>();
rel.add("eins", 1);
rel.add("eins", 2);
rel.add("eins", 3);
rel.add("zwei", 1);
rel.add("drei", 1);
rel.add("zwei", 3);
System.out.println(rel);
}}