It's usually the code. Here's a simple example:
import java.util.*;
public class GarbageCollector {
public static void main(String... args) {
System.out.printf("Testing...%n");
List<Double> list = new ArrayList<Double>();
for (int outer = 0; outer < 10000; outer++) {
// list = new ArrayList<Double>(10000); // BAD
// list = new ArrayList<Double>(); // WORSE
list.clear(); // BETTER
for (int inner = 0; inner < 10000; inner++) {
list.add(Math.random());
}
if (outer % 1000 == 0) {
System.out.printf("Outer loop at %d%n", outer);
}
}
System.out.printf("Done.%n");
}
}
Using java 1.6.0_24-b07 On a Windows7 32 bit.
java -Xloggc:gc.log GarbageCollector
Then look at gc.log
- Triggered 444 times using BAD method
- Triggered 666 times using WORSE method
- Triggered 354 times using BETTER method
Now granted, this is not the best test or the best design but when faced with a situation where you have no choice but implementing such a loop or when dealing with existing code that behaves badly, choosing to reuse objects instead of creating new ones can reduce the number of times the garbage collector gets in the way...