[Octave-bug-tracker] [bug #40111] support runtime selection of Java with JAVA_HOME on Linux and Unix systems

[Philip Nienhuis]

Follow-up Comment #31, bug #40111 (project octave):

An update after some more experiments:

* AFAICS the new Java JR selection works fine. After restarting my laptop dev
Octave (64b) could find the 64bit Java w/o problems on Win 7. Older 32bit
Octave and 64bit Octave also still find matching Java.

* On Windows, the path to the JRE should have forward slashes as file
separators. Backslashes in the JAVA_HOME setting don't work. Theoretically
this may interfere with other Windows programs that use a JAVA_HOME setting
and that do expect backslashes, although I'm not aware of any such programs. 

* Selecting Java JRE only works the first time, before any Java call is
invoked. I think that's something to watch out for; it may provoke bug reports
from unwary users.
See here after starting Octave:

>> javaMethod ("getProperty", "java.lang.System", "java.version")
ans = 10
>> javaclasspath
   STATIC JAVA PATH

      - empty -

   DYNAMIC JAVA PATH

      - empty -
>> setenv ("JAVA_HOME", 'C:/Program Files/Java/jre1.8.0_162')
>> javaMethod ("getProperty", "java.lang.System", "java.version")
ans = 10


and here:

>> setenv ("JAVA_HOME", 'C:/Program Files/Java/jre1.8.0_162')
>> javaMethod ("getProperty", "java.lang.System", "java.version")
ans = 1.8.0_162
>> javaclasspath
   STATIC JAVA PATH

      - empty -

   DYNAMIC JAVA PATH

      - empty -
>> setenv ("JAVA_HOME", 'C:/Program Files/Java/jre-10')
>> javaMethod ("getProperty", "java.lang.System", "java.version")
ans = 1.8.0_162


* On 64bit Windows 10 (multiboot on the same laptop) 32-bit Octave-4.4.0 can't
find 32bit Java at all. I suppose that's a Windows 10 thing. On 64b Windows 7
it all works fine.
(I didn't notice before because I never run 32bit Octave these days)

* On wWindows 10, 64-bit dev Octave works fine incl. JAVA JRE selection
(again, before any Java method invocation).

* I cannot reproduce that pointing 64bit Octave to 32bit JRE mixes up Octave
(note difference between ../Program Files (X86)/.. = 32 bit and ..Program
Files/.. = 64bit JRE):

## Directly after starting Octave. Try to invoke 32b JRE  w 64b Octave
>> setenv ("JAVA_HOME", 'C:/Program Files (x86)/Java/jre1.8.0_162')
>> javaMethod ("getProperty", "java.lang.System", "java.version")
error: javaMethod: library open failed: C:/Program Files
(x86)/Java/jre1.8.0_162/bin/client/jvm.dll
## OK, try 64b JRE then
>> setenv ("JAVA_HOME", "C:/Program Files/Java/jre1.8.0_162")
>> javaMethod ("getProperty", "java.lang.System", "java.version")
ans = 1.8.0_162
## Again try 32-bit JRE
>> setenv ("JAVA_HOME", "C:/Program Files (X86)/Java/jre1.8.0_162")
>> javaMethod ("getProperty", "java.lang.System", "java.version")
ans = 1.8.0_162


... so Octave seems to cling on to a working JRE it found before.


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