What is difference between ArrayList and list?

Inhaltsverzeichnis:

1. What is difference between ArrayList and list?
2. What is WeakHashMap?
3. Is WeakHashMap thread safe?
4. What is WeakHashMap and IdentityHashMap?
5. What is LinkedHashMap in Java?
6. How does HashMap works in Java?
7. How do I know if LinkedHashMap is empty?
8. How do you iterate a map?
9. Can we iterate HashMap?
10. How do you iterate a list?
11. What is iterator in Java?
12. What is hasNext () in Java?
13. Is iterator a class?
14. What is iterator remove ()?
15. Is iterator an abstract class?
16. What does iterator hasNext do?
17. Can we remove any element by using for each loop?
18. Can we modify ArrayList while iterating?
19. Can we modify a list while iterating Java?
20. How do I stop ConcurrentModificationException in Java?
21. How does ConcurrentHashMap works in Java?
22. What iterator can throw a ConcurrentModificationException?
23. What is Java Util ConcurrentModificationException?
24. Is ArrayList thread safe?
25. What is CopyOnWriteArrayList in Java?
26. How do I use an iterator in Java?

What is difference between ArrayList and list?

List and ArrayList are the members of Collection framework. List is a collection of elements in a sequence where each element is an object and elements are accessed by there position (index). ... The primary difference between List and ArrayList is that List is an interface and ArrayList is a class.

What is WeakHashMap?

WeakHashMap is an implementation of the Map interface that stores only weak references to its keys. Storing only weak references allows a key-value pair to be garbage-collected when its key is no longer referenced outside of the WeakHashMap. This class provides the easiest way to harness the power of weak references.

Is WeakHashMap thread safe?

java. Unfortunately this class is not thread-safe. ... It's entirely possible that unsynchronized invocation of the WeakHashMap.

What is WeakHashMap and IdentityHashMap?

IdentityHashMap stores strong key reference. WeakHashMap stores the weak key reference. EnumMap stores the strong key reference. Search and get the values. It uses equality operator (==) to search and get the values.

What is LinkedHashMap in Java?

LinkedHashMap is a Hash table and linked list implementation of the Map interface, with predictable iteration order. This implementation differs from HashMap in that it maintains a doubly-linked list running through all of its entries.

How does HashMap works in Java?

A HashMap is a map used to store mappings of key-value pairs. ... HashMap in Java works on hashing principles. It is a data structure which allows us to store object and retrieve it in constant time O(1) provided we know the key. In hashing, hash functions are used to link key and value in HashMap.

How do I know if LinkedHashMap is empty?

Using the size() method : Store the value of the size of LinkedHashMap in it. If the size of the given LinkedHashMap is 0 then it is empty.

How do you iterate a map?

Iterating over Map. entrySet() method returns a collection-view(Set) of the mappings contained in this map. So we can iterate over key-value pair using getKey() and getValue() methods of Map. Entry.

Can we iterate HashMap?

Using a for loop to iterate through a HashMap entrySet() is used to return a set view of the mapped elements. Now, getValue() and getKey() functions, key-value pairs can be iterated.

How do you iterate a list?

How to iterate over a Java list?

1. Obtain an iterator to the start of the collection by calling the collection's iterator() method.
2. Set up a loop that makes a call to hasNext(). Have the loop iterate as long as hasNext() returns true.
3. Within the loop, obtain each element by calling next().

What is iterator in Java?

An Iterator is an object that can be used to loop through collections, like ArrayList and HashSet. It is called an "iterator" because "iterating" is the technical term for looping. To use an Iterator, you must import it from the java.

What is hasNext () in Java?

Java Scanner hasNext() Method. The hasNext() is a method of Java Scanner class which returns true if this scanner has another token in its input. There are three different types of Java Scanner hasNext() method which can be differentiated depending on its parameter. ... Java Scanner hasNext (String pattern) Method.

Is iterator a class?

Answer: Iterator is an interface. It is not a class. It is used to iterate through each and every element in a list.

What is iterator remove ()?

An element can be removed from a Collection using the Iterator method remove(). This method removes the current element in the Collection. If the remove() method is not preceded by the next() method, then the exception IllegalStateException is thrown. A program that demonstrates this is given as follows.

Is iterator an abstract class?

The Java Iterator is an interface, ie it only defines the set of operations, not the collection. And in general, "Java iterators" are implementations of that interface, so they define how the behaviours are performed. They aren't abstract in that regard so aren't ADTs.

What does iterator hasNext do?

Iterator interface provides the following methods: boolean hasNext() - Returns true if the iteration has more elements. E next() - Returns the next element in the iteration. void remove() - Removes from the underlying collection the last element returned by the iterator (optional operation).

Can we remove any element by using for each loop?

Unfortunately, you cannot use it everywhere. Consider, for example, the expurgate method. The program needs access to the iterator in order to remove the current element. The for-each loop hides the iterator, so you cannot call remove .

Can we modify ArrayList while iterating?

Replace element in arraylist while iterating Do not use iterator if you plan to modify the arraylist during iteration. Use standard for loop, and keep track of index position to check the current element. Then use this index to set the new element.

Can we modify a list while iterating Java?

4 Answers. At the end the whole list will have the letter "D" as its content. It's not a good idea to use an enhanced for loop in this case, you're not using the iteration variable for anything, and besides you can't modify the list's contents using the iteration variable.

How do I stop ConcurrentModificationException in Java?

How to avoid ConcurrentModificationException in a multi-threaded environment?

1. Instead of iterating over the collection class, we can iterate over the array. ...
2. Another way can be locking the list by putting it in the synchronized block. ...
3. JDK 1.

   How does ConcurrentHashMap works in Java?

   ConcurrentHashMap: It allows concurrent access to the map. Part of the map called Segment (internal data structure) is only getting locked while adding or updating the map. So ConcurrentHashMap allows concurrent threads to read the value without locking at all. This data structure was introduced to improve performance.

   What iterator can throw a ConcurrentModificationException?

   Fail-Fast iterators immediately throw ConcurrentModificationException if there is structural modification of the collection. Structural modification means adding, removing any element from collection while a thread is iterating over that collection.

   What is Java Util ConcurrentModificationException?

   ConcurrentModificationException. The java. util. ConcurrentModificationException is typically thrown when code attempts to modify a data collection while that collection is actively in use, such as being iterated.

   Is ArrayList thread safe?

   Any method that touches the Vector 's contents is 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 .

   What is CopyOnWriteArrayList in Java?

   CopyOnWriteArrayList is a thread-safe variant of ArrayList where operations which can change the ArrayList (add, update, set methods) creates a clone of the underlying array. CopyOnWriteArrayList is to be used in a Thread based environment where read operations are very frequent and update operations are rare.

   How do I use an iterator in Java?

   Java - How to Use Iterator?

   1. Obtain an iterator to the start of the collection by calling the collection's iterator( ) method.
   2. Set up a loop that makes a call to hasNext( ). Have the loop iterate as long as hasNext( ) returns true.
   3. Within the loop, obtain each element by calling next( ).