java collections

7/21/2019 Java Collections

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The entire listing of interfaces, implementation classes and algorithm classes are

present in java.util package except Comparable interface.

Map does not extend java.util.Collection.

All implementation classes marked as (Legacy) contains synchronized methods. It does

not support concurrent access.



Refer: http://download.oracle.com/javase/1.4.2/docs/api/java/util/Collection.html for

description of other methods of Collection interface.



Performance of sorting and searching operations with collections of size n is measured

using Big-O notation. The notation describes the complexity of the algorithm in

relation to the maximum time in which an algorithm operates, for large values of n. For

instance, if you iterate through an entire collection to find an element, the Big-O

notation is referred to as O(n), meaning that as n increases, time to find an element in

a collection of size n increases linearly. This demonstrates that Big-O notation assumes

worst case performance. It is always possible that performance is quicker.

For more information on Big O notation refer:

http://en.wikipedia.org/wiki/Big_O_notation



LinkedList also implements Deque<E>, Queue<E> from Java version 1.6 onwards.

The Queue and Deque interface provides first-in-first-out queue operations for add,

poll.

http://download.oracle.com/javase/6/docs/api/java/util/Deque.html

http://download.oracle.com/javase/6/docs/api/java/util/Queue.html

http://download.oracle.com/javase/6/docs/api/java/util/Queue.html

http://download.oracle.com/javase/6/docs/api/java/util/Deque.html



For information on other methods Refer:

http://download.oracle.com/javase/6/docs/api/java/util/LinkedList.html



With Generics the collections becomes type-safe.

If the code compiles the programmer will not get any class-cast exception at runtime.



Note: Try writing a generic code that can work on many types of containers like Set

and List.



The code of compareTo() is written assuming that the employeeId is unique.

If the comparison is based on fields which are not unique: if the difference of two

values result in the value 0, then return the difference of

other fields.Example:

public int compareTo(Employee employee) {

int difference =

this.getFirstName().compareTo(employee.getFirstName());

if( difference == 0 ) {

difference =

Double.compare(this.getSalary(), employee.getSalary());

}

}

return difference;



Inner classes can access all the members of outer class even if the outer class

members are private.

Inner classes can be static or non-static.



Whenever hashCode() returns same INTEGER, equals() method is used to check

objects equality.



Refer:http://www.cs.auckland.ac.nz/~jmor159/PLDS210/red_black.html for

information on RedBlack tree.



Read more about Load Factor and Rehashing :http://goo.gl/uumsm



To specify the load factor create instance as new HashMap(0.75f); i.e. if 75% of

buckets are filled bucket size increases and rehashing takes place.



Object get(Object key) method of Map returns “null” if key is not found.



Refer : 1) http://javahowto.blogspot.com/2006/06/4-ways-to-traverse-map.html

2) http://stackoverflow.com/questions/3870064/performance-considerations-

for-keyset-and-entryset-of-map

3) http://ulibgcj.sourceforge.net/javadoc/java/util/HashMap.html



Refer: http://goo.gl/Y3Ybq for information on Enum type.



Similarly complete this flow chart for choosing a Map.

java collections

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