Memory Usage of Variables in Java

[trandinhduy]

Hi,

In short, here is my case:

I want to make a function to read XML file. In addition, I want to find a way to save as much memory for my application.

I don't know which ways is better for me:

Case 1:

Class XmlParser
{
//some kinds of parser
private Xml parser = null;

private static XmlParser instance;

public XmlParser()
{
parser = new Xml();
}

...

public static void getInstance()
{
if(instance == null) instance = new XmlParser();
return instance;
}

In this case, I create an instance to point to this class, so it won't be create again when I call the XmlParser

e.g XmlParser.getInstance().parse(fileUrl);

Whenever I need to use a parser, I just call a method in it and pass the file URL. It will create a new streamInput to pass to the parser;

Note: the "parser = new Xml()" is called only one time when the variable is created first time.

Case 2:

public class XmlParser
{
private Xml parser = null;

public XmlParser(String fileUrl)
{
//create input stream to the file and pass to the new parser
}

// some methods which can be called to start parsing
....
}

In this case, when I want to use the Parser, I must create a new instance of this class.

e.g XmlParser parser = new XmlParser("abc.xml");
An_Object a = parser.parse();

Could you please compare these two cases for me. Which one is the better way when I want to use the xml parser and want to save memory too (like optimization, maybe).

Note: I am using pull parser. About parsing xml in my application, the parser will be called when the app is started (only 1 time) and when a user changes the configuration of the app (e.g. he changes configuration of the app 1 times = 1 call to the parser, 2 time = 2 calls to the parser, etc.).

Thank you.

[grahamhughes]

Create the parser only when you need it.

Two reasons not to create one and re-use it:

1. It takes up memory even when you're not using it.

2. Second time you use it, it may still have data remaining in it from the last time. A "use-once" object requires less testing.

Cheers,
Graham.