Solved

Can a Variable be populated from another method in another class.

Posted on 2003-11-10
4
165 Views
Last Modified: 2010-08-05
I've ran across something that I've never seen in Java before.  I step throught somebody's code to get a line of data:
public class VendorMaster
{
next = loaddata.getLine(currentLine);
}

public class LoadData
{
public boolean getLine(byte[] line)
{
...
line is populated here
return gotnext;
}

When I step through the code in VendorMaster after executing getLine, currentLine is populated!  I didn't know you can populate a variable in the called method and make its contents visible in the calling class without actually returning it back in "return" statement.  Why is this happening?  Is this safe to implement especially with having multiple threads?  Thanks.
0
Comment
Question by:Mero
  • 3
4 Comments
 
LVL 15

Assisted Solution

by:jimmack
jimmack earned 50 total points
ID: 9716150
currentLine is passed across as a reference to the beginning of the array, so when the LoadData class writes to it, it's writing to the same memory space.

"currentLine" and "line" are referring to the same block of memory.
0
 
LVL 16

Accepted Solution

by:
imladris earned 100 total points
ID: 9716402
Needing a return statement is true for "primitive" variables (int, long, byte, char etc.). Others (arrays or objects) are passed by reference.

Whether this will pose a challenge w.r.t. multiple threads or not depends on "where" the currentLine is. If it is a shared resource (usually or global or member variable) that multiple threads are accessing, you will need to guard its access with syncronization blocks. However, if currentLine is a purely local, temporary, variable located on the stack, then multithreading will have no impact. Each thread has its own stack, after all.
0
 
LVL 15

Expert Comment

by:jimmack
ID: 9716667
Good catch imladris ;-)  I didn't read the last sentence :-(
0
 
LVL 15

Expert Comment

by:jimmack
ID: 9717113
:-)
0

Featured Post

Netscaler Common Configuration How To guides

If you use NetScaler you will want to see these guides. The NetScaler How To Guides show administrators how to get NetScaler up and configured by providing instructions for common scenarios and some not so common ones.

Question has a verified solution.

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

Suggested Solutions

Java had always been an easily readable and understandable language.  Some relatively recent changes in the language seem to be changing this pretty fast, and anyone that had not seen any Java code for the last 5 years will possibly have issues unde…
Introduction This article is the second of three articles that explain why and how the Experts Exchange QA Team does test automation for our web site. This article covers the basic installation and configuration of the test automation tools used by…
Viewers learn about the “for” loop and how it works in Java. By comparing it to the while loop learned before, viewers can make the transition easily. You will learn about the formatting of the for loop as we write a program that prints even numbers…
This tutorial will introduce the viewer to VisualVM for the Java platform application. This video explains an example program and covers the Overview, Monitor, and Heap Dump tabs.

773 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