phax
commented
10 years ago This is a very good question - I would not like to add additional libraries for this, so we will stick with "write by hand" :) But I do have a simple "HashCodeGenerator" in one of my other projects, which I would like to reuse. It is checked into the "util" package.
Example for a class with base class Object:
@Override
public int hashCode ()
{
return new HashCodeGenerator (this).append (member1).append (member2).getHashCode ();
}Example for a class which is derived from a class different than Object:
@Override
public int hashCode ()
{
return HashCodeGenerator.getDerived (super.hashCode ()).append (member3).append (member4).getHashCode ();
}Concerning equals, I don't have a real helper because there are four different versions of equals required, depending on the scope of the class:
- class is not final and it's base class is Object
- class is final and it's base class is Object
- class who's base class is NOT Object
Here are the examples for all cases:
public class Case1 {
private String s;
private int i;
public boolean equals (Object o) {
// always the first clause
if (o == this)
return true;
// Parameter is null or from a different implementation class
if (o == null || !getClass ().equals (o.getClass ()))
return false;
// Same class and parameter not null - start comparing
Case1 rhs = (Case1) o;
return EqualsUtils.equals (s, rhs.s) && EqualsUtils.equals(i, rhs.i);
}
}
public final class Case2 {
String s;
int i;
public boolean equals (Object o) {
// always the first clause
if (o == this)
return true;
// Parameter is null or from a different implementation class
// Theoretically the line from Case1 could also be used here, but I think this is more readable
if (!(o instanceof Case2))
return false;
// Same class and parameter not null - start comparing
Case2 rhs = (Case2) o;
return EqualsUtils.equals (s, rhs.s) && EqualsUtils.equals(i, rhs.i);
}
}
public class Case3 extends Case1 {
private int x;
public boolean equals (Object o) {
// always the first clause
if (o == this)
return true;
// Parameter is null or from a different implementation class
if (!super.equals (o))
return false;
// Same class and parameter not null - start comparing
Case3 rhs = (Case3) o;
return EqualsUtils.equals (s, rhs.s) && EqualsUtils.equals(i, rhs.i);
}
}So it can be drilled down to Case1 and Case3 if you want. Btw. EqualsUtils is a small utility class in the util package, that performs null-safe-equals.
Do you think this is reasonable?
leventov
Seems that implementing
equals()andhashCode()methods forIJExpressionsubclasses is an absolute requirement for starting any analysis (#18). What way of implementing this do you prefer for the lib? Some particular auto generation utility, such as from Apache Commons, or Lombok, or Google's auto-value? Generating from Eclipse/Intellij? Or writing by hand?(Of cause I would be very grateful if you implement this, but if don't want to, I will be forced to do it myself, and will try to accout your advice.)