CODEWITHSUNDEEP
javaapilistcollections
fulmicoton
fulmicoton

Reputation: 15968

Why is List.remove overloaded the way it is?

Is there historical reasons to the two ambiguous List.remove?

It seems like terrible design to me.
For a List<Integer> it just seems really confusing.

EDIT:

Everybody seems pretty fine with this. Let me precise things a bit.

Let's say I have a List<Boolean>.

Integer idx = Integer.valueOf(2);
list.remove(idx)

Though idx is an object, Java compiles and will remove the item at index 2.

Now if it had been a List<Integer>, the very same code would have called a different method with a totally different behavior.

Let's not talk about what would happen with Generics.

I feel like different behavior implies different names is a precious rule, especially within the same class.

Upvotes: 8

Views: 612

Answers (5)

fmucar
fmucar

Reputation: 14548

One of them is for removing from specific index

The other is removing an object, index is not important.

Upvotes: 0

Kevin Bourrillion
Kevin Bourrillion

Reputation: 40851

Yep, this exact case is frequently cited as an example of how perfectly well-intentioned language changes (generics, autoboxing) can combine with each other and with existing APIs to produce bugs. Indeed Josh wishes he had given the methods different names, but when that interface was first created, it was never imagined that there could be any conflict between an Object and an int. You can find an exploration of this issue in Java Puzzlers (Bloch/Gafter).

Upvotes: 3

Joachim Sauer
Joachim Sauer

Reputation: 308031

First of all:

I'm not sure if this was already known, but for completeness sake, I thought I'd mention it.

An important part to notice is that the API predates generics (and more importantly) auto-boxing by quite a bit (the collections API was introduced in Java 1.2 and auto-boxing was introduced in Java 5).

So when they first designed the API, there was absolutely no way to confuse the two. Even if your List contained Integer objects, it's simple: if you call the method with a primitive argument type (int), then it's the index, if you pass in an Object (even if it's Integer), then you pass in the object to remove.

Granted, it's still not the greatest idea (but quite a few Java APIs are ... less than perfect), but the chance for confusion was much lower back then.

The increased chance of confusion only exists since the int/Integer barrier became less visible thanks to auto-boxing and auto-unboxing.

Sidenote: an important "feature" of the collections API is "short names for commonly used methods". The previous "solution" of Vector/Enumeration had notoriously long names for pretty common operations:

  • Vector.elementAt() vs. List.get()
  • Vector.addElement() vs. Collection.add()
  • Enumeration.hasMoreElements()/nextElement() vs. Iterator.hasNext()/next()
  • Vector.removeElement() vs. Collection.remove()
  • Vector.removeElementAt() vs. List.remove(int)

And the last one are where they probably went a bit too far.

Upvotes: 11

hvgotcodes
hvgotcodes

Reputation: 120188

What, this is not ambigious at all. One removes at a specified index, the other removes an object where-ever it is first found in the list... oO

EDIT - the definition of a method is more than just the name. The type and number of arguments is part of the definition. When you take the entire method definition, there is no ambiguity.

Upvotes: 0

matt b
matt b

Reputation: 139931

How is this ambiguous? The documentation of each method seems clear to me:

E remove(int index)
Removes the element at the specified position in this list (optional operation).

boolean remove(Object o)
Removes the first occurrence in this list of the specified element (optional operation). If this list does not contain the element, it is unchanged.

They do two completely different things, hence a need for both.

Upvotes: -3

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