String memory allocation in java

Question

In an Servlet class, I am having the checks

if("Mail".equals( request.getParameter(mode)) || "Chat".equals( request.getParameter(mode))) {}

My question is about the memory allocated for the strings "Mail" and "Chat". Will it create new string objects for every request to this servlet. What about GC?.

If you ever traced the amount of code executed just schedulaing a servlet you would not worry about such micro optimisations! — James Anderson
– James Anderson, Commented Nov 12, 2010 at 7:14

Jon Skeet · Accepted Answer · 2010-11-12 06:31:03Z

6

No, it won't create a new object each time. String constants are interned - they're created once and put in a special pool.

Not only will it not create a new string each time you run the code, but if you use the constants "Mail" or "Chat" elsewhere in your code, they'll use the same string objects too.

From the Java Language Specification section 3.10.5:

Each string literal is a reference (§4.3) to an instance (§4.3.1, §12.5) of class String (§4.3.3). String objects have a constant value. String literals-or, more generally, strings that are the values of constant expressions (§15.28)-are "interned" so as to share unique instances, using the method String.intern.

answered Nov 12, 2010 at 6:31

Jon Skeet

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4 Comments

Jigar Joshi Over a year ago

Jon, In some other thread I asked you "" does it also get stored in pool , and how much memory it consumes. I would like to know

Jon Skeet Over a year ago

@org.life.java: Yes, it does get stored in the pool. It won't take up much memory - enough for an empty char array and the String object itself, basically.

cringe Over a year ago

So it only makes sense to store Strings as static final if you use them a lot in your class and don't want to risk typos, right?

Jon Skeet Over a year ago

@cringe: In terms of memory usage, yes. But keeping consistency is pretty important...

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