Counter-example of Listing 8-1 of some JVM book, using JRockit

command prompt

$ javac -g Test.java 
$ ~/sdk/jrmc-4.0.1-1.6.0/bin/java -version
java version "1.6.0_20"
Java(TM) SE Runtime Environment (build 1.6.0_20-b02)
Oracle JRockit(R) (build R28.0.1-21-133393-1.6.0_20-20100512-2126-linux-x86_64, compiled mode)
$ ~/sdk/jrmc-4.0.1-1.6.0/bin/java -verbose:gc Test
[INFO ][memory ] Running with 32 bit heap and compressed references.
[INFO ][memory ] GC mode: Garbage collection optimized for throughput, strategy: Generational Parallel Mark & Sweep.
[INFO ][memory ] Heap size: 65536KB, maximal heap size: 3145728KB, nursery size: 32768KB.
[INFO ][memory ] <start>-<end>: <type> <before>KB-><after>KB (<heap>KB), <time> ms, sum of pauses <pause> ms.
[INFO ][memory ] <start>  - start time of collection (seconds since jvm start).
[INFO ][memory ] <type>   - OC (old collection) or YC (young collection).
[INFO ][memory ] <end>    - end time of collection (seconds since jvm start).
[INFO ][memory ] <before> - memory used by objects before collection (KB).
[INFO ][memory ] <after>  - memory used by objects after collection (KB).
[INFO ][memory ] <heap>   - size of heap after collection (KB).
[INFO ][memory ] <time>   - total time of collection (milliseconds).
[INFO ][memory ] <pause>  - total sum of pauses during collection (milliseconds).
[INFO ][memory ]            Run with -Xverbose:gcpause to see individual phases.
[INFO ][memory ] [OC#1] 0.798-0.803: OC 436KB->65826KB (98308KB), 0.005 s, sum of pauses 3.461 ms, longest pause 3.461 ms.
[INFO ][memory ] [YC#1] 0.855-0.856: YC 65828KB->65900KB (98308KB), 0.002 s, sum of pauses 1.488 ms, longest pause 1.488 ms.
$ ~/sdk/jrmc-4.0.1-1.6.0/bin/java -XX:FullSystemGC=true -verbose:gc Test
[INFO ][memory ] Running with 32 bit heap and compressed references.
[INFO ][memory ] GC mode: Garbage collection optimized for throughput, strategy: Generational Parallel Mark & Sweep.
[INFO ][memory ] Heap size: 65536KB, maximal heap size: 3145728KB, nursery size: 32768KB.
[INFO ][memory ] <start>-<end>: <type> <before>KB-><after>KB (<heap>KB), <time> ms, sum of pauses <pause> ms.
[INFO ][memory ] <start>  - start time of collection (seconds since jvm start).
[INFO ][memory ] <type>   - OC (old collection) or YC (young collection).
[INFO ][memory ] <end>    - end time of collection (seconds since jvm start).
[INFO ][memory ] <before> - memory used by objects before collection (KB).
[INFO ][memory ] <after>  - memory used by objects after collection (KB).
[INFO ][memory ] <heap>   - size of heap after collection (KB).
[INFO ][memory ] <time>   - total time of collection (milliseconds).
[INFO ][memory ] <pause>  - total sum of pauses during collection (milliseconds).
[INFO ][memory ]            Run with -Xverbose:gcpause to see individual phases.
[INFO ][memory ] [OC#1] 0.318-0.321: OC 436KB->65826KB (98308KB), 0.003 s, sum of pauses 1.436 ms, longest pause 1.436 ms.
[INFO ][memory ] [OC#2] 0.373-0.379: OC 65828KB->209KB (98308KB), 0.005 s, sum of pauses 3.767 ms, longest pause 3.767 ms.
$ 

Test.java

public class Test {
  public static void main(String[] args) {
    byte[] placeholder = new byte[64 * 1024 * 1024];
    System.gc();
  }
}

The example in the book said this code doesn't get the byte array referenced to by placeholder GC'd. But here we show it can get GC'd, when using JRockit with -XX:FullSystemGC=true.