Is there a memory leak with Java String.format()

Question

I have this statement in a while loop, I noticed that in the windows task manager, the memory used by the java app process is keep increasing, about several k per second. Is there a memory issue with String.format?

String str = String.format("%dDays %02d : %02d : %02d",days,hours,minutes,seconds);

The garbage collector doesn't run until there is a reason for it to run, you probably haven't hit that limit so Java isn't collecting the freed memory from the buffers. — Jesus Ramos, Jan 15 '13 at 00:18
I put the str on a JLabel, as you said, it must be the way how GC works — Dewitt, Jan 15 '13 at 00:31
The `java.util.Formatter` will take a StringBuilder in its constructor, if that can help you. — Hovercraft Full Of Eels, Jan 15 '13 at 00:33

score 1 · Answer 1 · answered Jan 15 '13 at 00:21

If you're not using str anywhere after then it's just that the garbage collector has not run so the memory that should be released hasn't been collected yet. This is probably because Java doesn't need it (since it has some reserve pages left) yet as Java has to use a certain amount of memory before it starts reclaiming memory since running the garbage collector is an expensive task.

score 0 · Answer 2 · answered Jan 15 '13 at 00:21

I'm going to assume that you do not keep references to the strings you create.

Basically, that call creates a new object every time it runs. Those objects remain in memory until the Java Virtual Machine decides to perform garbage collection. The JVM will not do so until it decides that it is necessary. Necessary is generally when your memory usage exceeds a certain threshold. That threshold will depend on your machine and the setting the JVM was started with.

I just put the str on a JLabel, I totally agree with you that it's the GC — Dewitt, Jan 15 '13 at 00:30

score 0 · Answer 3 · answered Jan 15 '13 at 00:37

It should help if you do something like:

String days = "Monday";
String hours = "10:00pm";
String minutes = "60";
String seconds = "01";

while(condition){
     String str = String.format("%dDays %02d : %02d : %02d",days,hours,minutes,seconds);
}

This will pass the reference to the string instead of taking 32 bits up for each string of each iteration in your loop. If you can't help that your determine your strings in the loop try switching to character or bytes (if possible) that will reduce the amount of memory you use.

If you want to force the garbage collector to run (very unsafe) look here

http://stackoverflow.com/questions/1481178/forcing-garbage-collection-in-java

Is there a memory leak with Java String.format()

3 Answers3