Solved

Object from String

Posted on 2011-09-05
5
246 Views
Last Modified: 2012-05-12
I would like to know
how to get object from a string

and

also when do we use

map.keySet().

Thanks in  advance
0
Comment
Question by:gudii9
[X]
Welcome to Experts Exchange

Add your voice to the tech community where 5M+ people just like you are talking about what matters.

  • Help others & share knowledge
  • Earn cash & points
  • Learn & ask questions
  • 4
5 Comments
 
LVL 47

Expert Comment

by:for_yan
ID: 36485269
String is and Object

In some cases you may say

String s;

Object o = s;

and you don't need to cast as String inherits form Objcet


0
 
LVL 47

Expert Comment

by:for_yan
ID: 36485278


http://download.oracle.com/javase/1.4.2/docs/api/java/util/Map.html#keySet%28%29

map.keySet() is a method which returns set of keys for a given object of type Map

0
 
LVL 7

Author Comment

by:gudii9
ID: 36485305
>>>keySet

public Set keySet()
Returns a set view of the keys contained in this map. The set is backed by the map, so changes to the map are reflected in the set, and vice-versa. If the map is modified while an iteration over the set is in progress, the results of the iteration are undefined. The set supports element removal, which removes the corresponding mapping from the map, via the Iterator.remove, Set.remove, removeAll retainAll, and clear operations. It does not support the add or addAll operations.
Returns:
a set view of the keys contained in this map.



when do we use it. To change map to set we use it?

Please elaborate
0
 
LVL 47

Accepted Solution

by:
for_yan earned 500 total points
ID: 36485335
Well sometimes you need to print out all keys existing in your map
In other cases you may use this method to traverse your whole map - then
you may say

HashMap <String, String> map = new HashMap<String, String>();
// populate your map in some way
 
Set set = map.keySet();

for(String s: set){
String value = map.get(s);
System.out.println("key " + s + " value " + value);

///do something with each pair

}

see also example here
http://www.java2s.com/Code/Java/Collections-Data-Structure/GetkeysetandvaluesetfrommapanduseIteratortoloopthroughthem.htm


0
 
LVL 47

Expert Comment

by:for_yan
ID: 36485340
No we usualyy don't use keySet() to change the map,
we'll chnge the map normally by addig new pairs, say with put(kew, Vlaue) method
0

Featured Post

Technology Partners: We Want Your Opinion!

We value your feedback.

Take our survey and automatically be enter to win anyone of the following:
Yeti Cooler, Amazon eGift Card, and Movie eGift Card!

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

By the end of 1980s, object oriented programming using languages like C++, Simula69 and ObjectPascal gained momentum. It looked like programmers finally found the perfect language. C++ successfully combined the object oriented principles of Simula w…
Go is an acronym of golang, is a programming language developed Google in 2007. Go is a new language that is mostly in the C family, with significant input from Pascal/Modula/Oberon family. Hence Go arisen as low-level language with fast compilation…
Video by: Michael
Viewers learn about how to reduce the potential repetitiveness of coding in main by developing methods to perform specific tasks for their program. Additionally, objects are introduced for the purpose of learning how to call methods in Java. Define …
Viewers learn how to read error messages and identify possible mistakes that could cause hours of frustration. Coding is as much about debugging your code as it is about writing it. Define Error Message: Line Numbers: Type of Error: Break Down…

719 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question