What is the equivalent of the C++ Pair<L,R> in Java?
In a thread on comp.lang.java.help
, Hunter Gratzner gives some arguments against the presence of a Pair
construct in Java. The main argument is that a class Pair
doesn't convey any semantics about the relationship between the two values (how do you know what "first" and "second" mean ?).
A better practice is to write a very simple class, like the one Mike proposed, for each application you would have made of the Pair
class. Map.Entry
is an example of a pair that carry its meaning in its name.
To sum up, in my opinion it is better to have a class Position(x,y)
, a class Range(begin,end)
and a class Entry(key,value)
rather than a generic Pair(first,second)
that doesn't tell me anything about what it's supposed to do.
This is Java. You have to make your own tailored Pair class with descriptive class and field names, and not to mind that you will reinvent the wheel by writing hashCode()/equals() or implementing Comparable again and again.
HashMap compatible Pair class:
public class Pair<A, B> {
private A first;
private B second;
public Pair(A first, B second) {
super();
this.first = first;
this.second = second;
}
public int hashCode() {
int hashFirst = first != null ? first.hashCode() : 0;
int hashSecond = second != null ? second.hashCode() : 0;
return (hashFirst + hashSecond) * hashSecond + hashFirst;
}
public boolean equals(Object other) {
if (other instanceof Pair) {
Pair otherPair = (Pair) other;
return
(( this.first == otherPair.first ||
( this.first != null && otherPair.first != null &&
this.first.equals(otherPair.first))) &&
( this.second == otherPair.second ||
( this.second != null && otherPair.second != null &&
this.second.equals(otherPair.second))) );
}
return false;
}
public String toString()
{
return "(" + first + ", " + second + ")";
}
public A getFirst() {
return first;
}
public void setFirst(A first) {
this.first = first;
}
public B getSecond() {
return second;
}
public void setSecond(B second) {
this.second = second;
}
}