CODEWITHSUNDEEP
java
user496949
user496949

Reputation: 86085

Can we use index like array index to access List<T>?

I am wondering if we can use index to access List

For example:

List<Integer> list; 

list[5]     //blah....

Upvotes: 35

Views: 101726

Answers (7)

Hjalmar
Hjalmar

Reputation: 989

There are plenty of good answers here, but I just want to point out that list.get(i) is the same as list[i] only if list is implemented with an array (i.e ArrayList). If it is a LinkedList you are not really indexing with get, but rather iterating.

So if you use get() with the interface type List, especially in a loop, you should check how it's implemented, as get() with ArrayList is O(1) whereas get() with LinkedList is O(n) (much slower).

Upvotes: 8

asgs
asgs

Reputation: 3984

List.get(int) allows you to access elements using the index.

Upvotes: 35

user85421
user85421

Reputation: 29680

an alternative to using get(int) is to create an Array using toArray() 

List<T> list = ...

Object[] array = list.toArray();

if T is known, toArray(T[]) can be used to return T[] instead of Object[].
The use of toArray is only meaningful, instead of get, if an array is really needed (lots of accesses).

Upvotes: 3

user unknown
user unknown

Reputation: 36229

No, you're restricted to List.get (i).

The brackets [] are defined on syntax level, not as method-name, so you can't override them. They are used just for arrays exclusively.

If you like to migrate to Scala, a more modern language for the JVM, you'll find an unified access to arrays and lists, but both with () parentheses.

Upvotes: 4

josefx
josefx

Reputation: 15656

Since [] is an operator and java does not support operator overloading you can't use it with List. Instead you have to use the set(int index, T value) and get(int index) methods, which may be verbose but provide exact the same functionality.

Upvotes: 70

npinti
npinti

Reputation: 52185

You can access List elements using their index through the use of the get method:

get

public Object get(int index)

Returns the element at the specified position in this list.

Parameters: index - index of element to return.

Returns: the element at the specified position in this list.

Throws: IndexOutOfBoundsException - if the index is out of range (index < 0 || index >= size()).

Keep in mind that the index in Lists is 0 based.

Upvotes: 6

Patrick
Patrick

Reputation: 3759

No, you can't do this in Java.

Upvotes: 2

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