Java Questions

1. Difference between Array list and Vector in Java?

- Both use same data structure to store the elements that is array.

- Array list is not synchronized; multiple threads can use the array list. So it has best performance.

-Vector is synchronized; one thread can access the vector at a time.

- Vector will grow double its size.

- Array list grow half of its size.

2. Differences between Hash Map and Hash table?

 - Hash map store the elements in form of key and value pair.

 -  Hash table store the elements in form of key and value pair.

 -  Hash map and Hash table does not maintain any insertion order.

- Hash map allow single null key and multiple null value.

- Hash table does not allow single null key and value.

- Hash Map is not synchronized but hash table is synchronized

3. What is linked hash map?

 - Linked hash map is same as Hash map instead it maintain insertion order.

4. What is difference between Hash Map and Tree Map?

 - Hash map allow single null key and multiple null value.

 - Hash map does not maintain insertion order.

 - Tree map store the elements in ascending order.

- Tree map does not allow null key and value.

5. Difference between Lists, set and map?

 - List allow duplicate values where are set allow unique elements.

 - List maintains insertion order, based on the implementation set maintains insertion order.

 - List is index basis where has set is not index basis.

 - Map store the elements based on key and value pair.

6. Java Access modifiers?

Access Modifiers	Same Class	Same Package	Subclass	Other packages
public	Y	Y	Y	Y
protected	Y	Y	Y	N
no access modifier	Y	Y	N	N
private	Y	N	N	N

7. What is Exception handling?

The exception handling in java is one of the powerful mechanisms to handle the runtime errors so that normal flow of the application can be maintained.

8. Types of Exceptions?

 - Checked Exceptions that occurs at run time.

 - Unchecked Exceptions
9. String, StringBuffeer, StringBuilder:
String:
a. Strings are immutable, so we can't change the value(Final class).
b. Strings are Synchronous so thread safety.
StringBuffer:
a. We can change the value of Stingbuffer object.
b. StringBuffer is Synchronous so thread safety is guarantee because of this performance is slow.
StringBuilder:
a. It is same as a string buffer except the asynchronous character(No thread safety.).
b. For single threaded concepts we can go with the String builder.