- How many types of array are there?
- When would you use a linked list vs ArrayList?
- Does HashMap allow duplicates?
- When should you use an ArrayList?
- Can you have an ArrayList of arrays?
- Does ArrayList maintain order?
- What happens if we put duplicate key in HashMap?
- Should I use array or ArrayList?
- Is ArrayList linked list?
- Why HashMap is faster than HashSet?
- Which is better array or list?
- What is difference between Array and List?
- Why is HashMap so fast?
- Will TreeMap allow duplicates?
- Is HashMap thread safe?
- Which is faster HashMap or TreeMap?
- Which one is faster linked list or ArrayList?
- What is difference between collection and array?
- Which is better HashMap or Hashtable?
- Why array is faster than ArrayList in Java?
- Is array a collection in Java?
How many types of array are there?
In PHP, there are three types of arrays: Indexed arrays – Arrays with a numeric index.
Associative arrays – Arrays with named keys.
Multidimensional arrays – Arrays containing one or more arrays..
When would you use a linked list vs ArrayList?
LinkedList is fast for adding and deleting elements, but slow to access a specific element. ArrayList is fast for accessing a specific element but can be slow to add to either end, and especially slow to delete in the middle. Array vs ArrayList vs LinkedList vs Vector goes more in depth, as does Linked List.
Does HashMap allow duplicates?
HashSet does not allow duplicate elements that means you can not store duplicate values in HashSet. HashMap does not allow duplicate keys however it allows to have duplicate values. … HashMap permits single null key and any number of null values.
When should you use an ArrayList?
Here are some advantages of using ArrayList over arrays. You can define ArrayList as re-sizable array. … Elements can be inserted at or deleted from a particular position. … ArrayList class has many methods to manipulate the stored objects. … If generics are not used, ArrayList can hold any type of objects.More items…•
Can you have an ArrayList of arrays?
If you are not sure about the type of objects in the array or you want to create an ArrayList of arrays that can hold multiple types, then you can create an ArrayList of an object array. … That’s all for creating an Array of ArrayList and ArrayList of Array in Java.
Does ArrayList maintain order?
Both ArrayList and LinkedList are implementation of List interface. They both maintain the elements insertion order which means while displaying ArrayList and LinkedList elements the result set would be having the same order in which the elements got inserted into the List.
What happens if we put duplicate key in HashMap?
When “adding a duplicate key” the old value (for the same key, as keys must be unique) is simply replaced; see HashMap. put: Associates the specified value with the specified key in this map. If the map previously contained a mapping for the key, the old value is replaced.
Should I use array or ArrayList?
Both array and ArrayList are two important data structures in Java and are frequently used in Java programs. … Since an array is static in nature i.e. you cannot change the size of an array once created, So, if you need an array which can resize itself then you should use the ArrayList.
Is ArrayList linked list?
ArrayList is implemented as a resizable array. … It’s elements can be accessed directly by using the get and set methods, since ArrayList is essentially an array. LinkedList is implemented as a double linked list. Its performance on add and remove is better than Arraylist, but worse on get and set methods.
Why HashMap is faster than HashSet?
HashMap is faster/ than HashSet because values are associated with a unique key. HashSet is slower than HashMap because the member object is used for calculating hashcode value, which can be same for two objects.
Which is better array or list?
The list is better for frequent insertion and deletion whereas Arrays are much better suited for frequent access of elements scenario. List occupies much more memory as every node defined the List has its own memory set whereas Arrays are memory-efficient data structure.
What is difference between Array and List?
Arrays can store data very compactly and are more efficient for storing large amounts of data. Arrays are great for numerical operations; lists cannot directly handle math operations. For example, you can divide each element of an array by the same number with just one line of code.
Why is HashMap so fast?
HashMap, being a hashtable-based implementation, internally uses an array-based data structure to organize its elements according to the hash function. HashMap provides expected constant-time performance O(1) for most operations like add(), remove() and contains(). Therefore, it’s significantly faster than a TreeMap.
Will TreeMap allow duplicates?
A TreeMap cannot contain duplicate keys. TreeMap cannot contain the null key. However, It can have null values.
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.
Which is faster HashMap or TreeMap?
TreeMap is based on binary tree that provides time performance O(log(n)) . Thus, HashMap almost always works faster than TreeMap. The larger the object that’s stored, the faster HashMap will be in comparison to TreeMap. However, a TreeMap uses the optimal amount of memory to hold its items, unlike a HashMap.
Which one is faster linked list or ArrayList?
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.
What is difference between collection and array?
An array is a fixed-size data structure that does not permit elements to be inserted or removed after its creation whereas a Collection is resizable and can grow (or shrink) in size dynamically to accommodate more elements if required.
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.
Why array is faster than ArrayList in Java?
An array is faster and that is because ArrayList uses a fixed amount of array. However when you add an element to the ArrayList and it overflows. It creates a new Array and copies every element from the old one to the new one.
Is array a collection in Java?
In order to store multiple values or objects of the same type, Java provides two types of data structures namely Array and Collection. … Arrays can hold the only the same type of data in its collection i.e only homogeneous data types elements are allowed in case of arrays.