Reputation: 11186
What are the differences between the two data structures ArrayList and Vector, and where should you use each of them?
Upvotes: 419
Views: 275967
Reputation: 15679
Differences
Use ArrayLists if there is no specific requirement to use Vectors.
Synchronization
If multiple threads access an ArrayList concurrently then we must externally synchronize the block of code which modifies the list either structurally or simply modifies an element. Structural modification means addition or deletion of element(s) from the list. Setting the value of an existing element is not a structural modification.
Collections.synchronizedList
is normally used at the time of creation of the list to avoid any accidental unsynchronized access to the list.
Data growth
Internally, both the ArrayList and Vector hold onto their contents using an Array. When an element is inserted into an ArrayList or a Vector, the object will need to expand its internal array if it runs out of room. A Vector defaults to doubling the size of its array, while the ArrayList increases its array size by 50 percent.
Upvotes: 431
Reputation: 8232
ArrayList
and Vector
both implements List interface and maintains insertion order.But there are many differences between ArrayList
and Vector
classes...
ArrayList
is not synchronized.ArrayList
increments 50% of current array size if number of element exceeds from its capacity.ArrayList
is not a legacy class, it is introduced in JDK 1.2.ArrayList
is fast because it is non-synchronized.ArrayList
uses Iterator interface to traverse the elements.Vector -
Vector
is synchronized.Vector
increments 100% means doubles the array size if total number of element exceeds than its capacity.Vector
is a legacy class.
Vector
is slow because it is synchronized i.e. in multithreading environment, it will hold the other threads in runnable or non-runnable state until current thread releases the lock of object.
Vector
uses Enumeration interface to traverse the elements. But it can use Iterator also.
See Also : https://www.javatpoint.com/difference-between-arraylist-and-vector
Upvotes: 19
Reputation: 4712
There are 2 major differentiation's between Vector and ArrayList.
Vector is synchronized by default, and ArrayList is not. Note : you can make ArrayList also synchronized by passing arraylist object to Collections.synchronizedList() method. Synchronized means : it can be used with multiple threads with out any side effect.
ArrayLists grow by 50% of the previous size when space is not sufficient for new element, where as Vector will grow by 100% of the previous size when there is no space for new incoming element.
Other than this, there are some practical differences between them, in terms of programming effort:
When to use which one?
Note : even though arraylist grows by 100%, you can avoid this by ensurecapacity() method to make sure that you are allocating sufficient memory at the initial stages itself.
Hope it helps.
Upvotes: 28
Reputation: 4878
Basically both ArrayList and Vector both uses internal Object Array.
ArrayList: The ArrayList class extends AbstractList and implements the List interface and RandomAccess (marker interface). ArrayList supports dynamic arrays that can grow as needed. It gives us first iteration over elements. ArrayList uses internal Object Array; they are created with an default initial size of 10. When this size is exceeded, the collection is automatically increases to half of the default size that is 15.
Vector: Vector is similar to ArrayList but the differences are, it is synchronized and its default initial size is 10 and when the size exceeds its size increases to double of the original size that means the new size will be 20. Vector is the only class other than ArrayList to implement RandomAccess. Vector is having four constructors out of that one takes two parameters Vector(int initialCapacity, int capacityIncrement) capacityIncrement is the amount by which the capacity is increased when the vector overflows, so it have more control over the load factor.
Some other differences are:
Upvotes: 10
Reputation: 424943
Vector
is a broken class that is not threadsafe, despite it being "synchronized" and is only used by students and other inexperienced programmers.
ArrayList
is the go-to List implementation used by professionals and experienced programmers.
Professionals wanting a threadsafe List implementation use a CopyOnWriteArrayList
.
Upvotes: 69
Reputation: 36612
As the documentation says, a Vector
and an ArrayList
are almost equivalent. The difference is that access to a Vector
is synchronized, whereas access to an ArrayList
is not. What this means is that only one thread can call methods on a Vector
at a time, and there's a slight overhead in acquiring the lock; if you use an ArrayList
, this isn't the case. Generally, you'll want to use an ArrayList
; in the single-threaded case it's a better choice, and in the multi-threaded case, you get better control over locking. Want to allow concurrent reads? Fine. Want to perform one synchronization for a batch of ten writes? Also fine. It does require a little more care on your end, but it's likely what you want. Also note that if you have an ArrayList, you can use the Collections.synchronizedList
function to create a synchronized list, thus getting you the equivalent of a Vector
.
Upvotes: 101
Reputation: 239790
ArrayList
is newer and 20-30% faster.
If you don't need something explitly apparent in Vector
, use ArrayList
Upvotes: 29