- Can ArrayList have duplicates?
- Is HashMap thread safe?
- When should you use a LinkedList instead of an ArrayList?
- Which collection is best for insertion and deletion?
- Which collection is faster in Java?
- When should I use linked list?
- Why pointers are not used in Java?
- What’s the difference between a linked list and an ArrayList Can you give me examples of when you’d use each one?
- Which collection is best for inserting data?
- Does linked list allow duplicates?
- Which list will not allow duplicates?
- Which is better HashMap or Hashtable?
- How do you remove duplicates from ArrayList?
- How do you avoid duplicates in ArrayList?
- Which is faster ArrayList or linked list?
- How do you make an ArrayList thread safe?
- Where do we use LinkedList and ArrayList?
- Is ArrayList thread safe?
Can ArrayList have duplicates?
4) Duplicates: ArrayList allows duplicate elements but HashMap doesn’t allow duplicate keys (It does allow duplicate values).
5) Nulls: ArrayList can have any number of null elements.
In HashMap the elements is being fetched by specifying the corresponding key..
Is HashMap thread safe?
HashMap is non synchronized. It is not-thread safe and can’t be shared between many threads without proper synchronization code whereas Hashtable is synchronized. It is thread-safe and can be shared with many threads.
When should you use a LinkedList instead of an ArrayList?
LinkedList should be used where modifications to a collection are frequent like addition/deletion operations. LinkedList is much faster as compare to ArrayList in such cases. In case of read-only collections or collections which are rarely modified, ArrayList is suitable.
Which collection is best for insertion and deletion?
1) As explained above the insert and remove operations give good performance ( O(1) ) in LinkedList compared to ArrayList( O(n) ). Hence if there is a requirement of frequent addition and deletion in application then LinkedList is a best choice.
Which collection is faster in Java?
If you need fast access to elements using index, ArrayList should be choice. If you need fast access to elements using a key, use HashMap. If you need fast add and removal of elements, use LinkedList (but it has a very poor seeking performance).
When should I use linked list?
Linked lists are preferable over arrays when:you need constant-time insertions/deletions from the list (such as in real-time computing where time predictability is absolutely critical)you don’t know how many items will be in the list. … you don’t need random access to any elements.More items…•
Why pointers are not used in Java?
So overall Java doesn’t have pointers (in the C/C++ sense) because it doesn’t need them for general purpose OOP programming. Furthermore, adding pointers to Java would undermine security and robustness and make the language more complex.
What’s the difference between a linked list and an ArrayList Can you give me examples of when you’d use each one?
1) ArrayList internally uses a dynamic array to store the elements. LinkedList internally uses a doubly linked list to store the elements. 2) Manipulation with ArrayList is slow because it internally uses an array. If any element is removed from the array, all the bits are shifted in memory.
Which collection is best for inserting data?
In general you will always look for the collection with the best performance for your programming task, which in most cases is ArrayList, HashSet or HashMap. But be aware, if you need some special features like sorting or ordering you may need to go for a special implementation.
Does linked list allow duplicates?
1) Both ArrayList and LinkedList are an implementation of List interface, which means you can pass either ArrayList or LinkedList if a method accepts the java. util. … 4) ArrayList and LinkedList also allow duplicates and null, unlike any other List implementation e.g. Vector.
Which list will not allow duplicates?
2) List allows duplicates while Set doesn’t allow duplicate elements. All the elements of a Set should be unique if you try to insert the duplicate element in Set it would replace the existing value. 3) List implementations: ArrayList, LinkedList etc. Set implementations: HashSet, LinkedHashSet, TreeSet etc.
Which is better HashMap or Hashtable?
Hashtable is synchronized, whereas HashMap is not. This makes HashMap better for non-threaded applications, as unsynchronized Objects typically perform better than synchronized ones. Hashtable does not allow null keys or values. HashMap allows one null key and any number of null values.
How do you remove duplicates from ArrayList?
The easiest way to remove repeated elements is to add the contents to a Set (which will not allow duplicates) and then add the Set back to the ArrayList : Set
How do you avoid duplicates in ArrayList?
A better way (both time complexity and ease of implementation wise) is to remove duplicates from an ArrayList is to convert it into a Set that does not allow duplicates….Using LinkedHashSetGet the ArrayList with duplicate values.Create a LinkedHashSet from this ArrayList. … Convert this LinkedHashSet back to Arraylist.More items…•
Which is faster ArrayList or linked list?
ArrayList is faster than LinkedList if I randomly access its elements. … ArrayList has direct references to every element in the list, so it can get the n-th element in constant time. LinkedList has to traverse the list from the beginning to get to the n-th element. LinkedList is faster than ArrayList for deletion.
How do you make an ArrayList thread safe?
Method 1: Using Collections.synchronizedList() method It is imperative that user manually synchronize on the returned list when iterating over it. A thread-safe variant of ArrayList in which all mutative operations (e.g. add, set, remove..) are implemented by creating a separate copy of underlying array.
Where do we use LinkedList and ArrayList?
ArrayList provides constant time for search operation, so it is better to use ArrayList if searching is more frequent operation than add and remove operation. The LinkedList provides constant time for add and remove operations. So it is better to use LinkedList for manipulation.
Is ArrayList thread safe?
ArrayList , on the other hand, is unsynchronized, making them, therefore, not thread safe. With that difference in mind, using synchronization will incur a performance hit. So if you don’t need a thread-safe collection, use the ArrayList .