Java JRE and SDK Support and Performance
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| JRE/SDK | Works | Compiles | Performance |
| Sun 5 | yes | yes | good |
| Sun 6 | yes | yes | good |
| Sun 7 | |||
| GCJ (compiled to C) | yes | all but console | very poor |
| GCJ-JRE (gij-4.4) | yes | yes for I2P releases through 0.8, if you supply the Pack200 jar - see note below | poor, not recommended |
| Iced Tea 5 | |||
| Iced Tea 6 | yes | yes (no on PPC "1.6.0_18" OpenJDK Runtime Environment (IcedTea?6 1.8) - missing Pack200 - see http://forum.i2p/viewtopic.php?t=4655 ) - see note below | good |
| Iced Tea 7 | yes | yes | good |
| Open JDK 5 | |||
| Open JDK 6 | yes | yes | good |
| Open JDK 7 | yes | yes | good |
| IBM | Reportedly does not http://zzz.i2p/topics/577 | ||
| Android | no | yes (core and router) | hopeless |
| Oracle/BEA JRockit 1.6 | yes | yes | good |
| Apache Harmony 5 | no - bug in Deflater fixed with workaround in 0.7.12-15; reports huge clock skews in UDP Transport; works with TCP only? | slow | |
| Apache Harmony 6 | |||
| JamVM 1.5.3 | yes | n/a | poor |
NOTES:
<smeghead> icedtea is openjdk with the non-GPL-compatible parts replaced, and openjdk is sun's jdk with bits relicensed
<smeghead> for most purposes you shouldn't notice any difference between sun, openjdk, and icedtea
<smeghead> however, icedtea offers some alternatives to hotspot which can give worse or better performance
Note that as of I2P release 0.8.1, a 1.6 or higher compatible SDK is required to compile I2P. 1.5 or higher compatible JRE is still required to run I2P.
Pack200 note: You can get a free version of pack200.jar from the Apache Harmony package; if you install the Harmony SDK on Ubuntu, the file will be at /usr/lib/harmony-5.0/jdk/jre/lib/boot/pack200.jar; copy it to your JRE's library directory.
Update: As of I2P release 0.8.3, I2P will use either the Sun or Apache Pack200 if it is in the classpath at runtime, and neither is required to compile I2P.