Vectors: contains() inconsistency with Object equals()

Question

Hi,
I have a problem with using Vector contains() on my own classes.
I have a class TermDetails, on which I have overloaded the equals() method:
     public boolean equals(Object other) {
          try {
               TermDetails otherTerm = (TermDetails) other;
               return (term.equals(otherTerm.term));
          catch (Exception e) {
               try {
                    String otherTermString = (String) other;
                    return (term.equals(otherTermString));
               catch (Exception f) {
                    System.out.println("Can't convert Object to TermDetails or String");
                    System.out.println(f.getMessage());
                    return(false);
     public boolean equals(String otherTermString) {
          return(term.equals(otherTermString));
The Vector.contains() should then use one of these equals methods to return correctly, but doesn't use either of them... any ideas why not?
(I've tried adding some console output in the equals methods, just to prove if they get called or not. They don't.)
Thanks in advance!
Ed

Answer 1

This won't work. It only tests whether the two objects are of the same class. In general, you need to test a number of things:
1) if obj == this, return true
2) if obj == null, return false
3) if obj.getClass() != this.getClass() return false
(Note: You don't need getClass().getName(). Also, there are times when the classes don't have to match, but it's sufficient that obj and this implement a particular interface--Map for instance).
4) if all relevant corresponding fields of obj and this are equal, return true, else false.
That's just a high level run-down, and you should definitely look at the book that schapel mentioned.
Also, this probably won't affect Vector.contains, but make sure that when you override equals, you also override hashCode. The rule is that if a.equals(b) returns true, then a.hashCode() must return the same value as b.hashCode(). Basically any field that is used in computing hashCode must also be used in equals.
Note that the converse is not true. That is two objects with the same hashCode don't have to be equal.
For instance, if you've got a class that represents contact info, the hashCode could use only the phoneNumber field. hashCode will then be fast to compute, will probably have a good distribution (some distinct people's contact info could have the same phone number, but there won't be a large overlap), and then you use phone number plus the rest of the fields (address, etc.) for equals.
Here's an example that shows that equals will work if
written correctly
import java.util.Vector;
public class testEquals {
public static void main(String args[]) {
Vector testVector = new Vector();
testVector.add(new A());
testVector.add(new B());
System.out.println("A == A? " +
+ testVector.contains(new A()));
System.out.println("B == B? " +
+ testVector.contains(new B()));
class A {
public boolean equals(Object object) {
if (getClass().getName() ==
= object.getClass().getName()) {
System.out.println("A == A");
return true;
} else {
return false;
class B {
public boolean equals(Object object) {
if (getClass().getName() ==
= object.getClass().getName()) {
System.out.println("B == B");
return true;
} else {
return false;