CareerCup

1. HashMap is Java's version of a Hash Table based on the Map interface. It maps keys to values using a hash function.

2. Array list is an array with dynamic resizing and shifting, while a linked list is a set of nodes linked together. Arrays are great for accessing data an any index in constant time, but inserts require O(n-index) time, so inserting to the front of an ArrayList is linear time for EACH insert, while it's constant time in a LinkedList. However, accessing data near the middle of a LinkedList takes O(n) time because we have to travel through the nodes to get to it.

3. To my knowledge, collisions are handled internally when you put an item into a HashMap. One issue with HashMap that you won't get with a linking HashTable is that you cannot put a key to map to two different values. For example if you had a key<string> "John Smith" and you wanted 4 different phone number values for it, you could not do that with a HashMap (You can, however, have multiple keys map to a single value.)

4. Runtime Polymorphism is just what it sounds like - Polymorphism that occurs at runtime. So polymorphism basically deals with inheritance. Suppose we have Class Employee, and Subclass Lawyer. Using polymorphism we'd have:

Class Employee {
// Some stuff
}

Class Lawyer extends Employee {
// Some stuff
}
So we can say:

Employee lawMan = new Lawyer(); //right?

Doing this at runtime simply could go many ways. An example would be a method that builds Employees for you taking a string parameter, and something like:
//pseudo code
Some method (String str)
Employee emp;
if (str.equals("Lawyer"))
emp = new Lawyer();

Something like that would happen at runtime.

which company?

Amazon AWS team...

answers at
javadecodedquestions.blogspot.sg/2012/03/java-interview-with-investment-bank-4.html

Map implementation will be sortedhashmap, hashmap, treemap

hey Any one explain diffeferences bettween all maps,sets?