Question

I have MyClass, which stores two integers, and I have a Vector<MyClass> called myVector.

Now, I do this:

... myVector.add(new MyClass(1,1)); for(MyClass m : myVector)     System.out.println(m); System.out.println(myVector.size());  myVector.remove(new MyClass(1,1)); for(MyClass m : myVector)     System.out.println(m); System.out.println(myVector.size()); ... 

The problem here is that the object isn’t being removed, as I see when I print the Vector and its size. How could I fix that?

Edit: I can see that it isn’t finding the object and I’ve tested with contains() to be sure. What I need is to compare it by value. If I could overload the == operator I could do it, but I have no idea how to fix this.

Edit 2: Okay, equals() will do what I want it to. But I’m not sure what to put in the hashCode method.

Edit 3: I can find it with contains(), but remove doesn’t remove it.

I can use this to remove it though:

int position = myVector.indexOf(new MyClass(1,1)); myVector.remove(position); 

Which is the same as remove(new MyClass(1,1), except the above code works and remove() doesn’t. Any thoughts?

Answer 1

There are few errors in grammar31‘s answer; fix them up here:

@Override public boolean equals(Object o) {   if ((o == null) || (o.getClass() != myClass.class)) {     return false;   }   myClass other = (myClass) o;   return (other.a == this.a) && (other.b == this.b); }  @Override public int hashCode() {   return a * 31 + b; } 

This assumes myClass has int members a and b.