On 15/04/2015 13:37, Magnus Ihse Bursie wrote:
When this simple program is run:
public class TestSystemVersion {
public static void main(String[] args) {
System.out.println("1. java.version: " +
System.getProperty("java.version"));
System.out.println("1. java.runtime.version: " +
System.getProperty("java.runtime.version"));
System.setProperties(null);
System.out.println("2. java.version: " +
System.getProperty("java.version"));
System.out.println("2. java.runtime.version: " +
System.getProperty("java.runtime.version"));
}
}
The output is:
1. java.version: 1.9.0-internal
1. java.runtime.version: 1.9.0-internal-magnusi_2015_04_02_09_24-b00
2. java.version: 1.9.0-internal
2. java.runtime.version: null
Is this really expected? I find it surprising. I'd have thought that
either *both* strings would have been reset, or none.
This behavior stems from the fact that System.setProperties(), when
given a null argument, calls initProperties. This is a native method
which sets java.version, but not java.runtime.version. However, at
system startup, initializeSystemClass() will be called, which apart
from initProperties also calls a bunch of other methods to set up
initial system properties, for instance sun.misc.Version.init(), which
will re-set java.version (even though it is already set at this
point), and also set java.runtime.version.
At one point then Mike Duigou was looking into this via JDK-8022854 but
I don't think it was ever completed.
-Alan
