25

How to know JDK version from within Java code

robert_x44
  • 9,094
  • 1
  • 31
  • 37
Muhammad Hewedy
  • 27,782
  • 43
  • 120
  • 210

3 Answers3

47

I presume you mean just the Java version, in which case try this:

String version = System.getProperty("java.version");
Bart Kiers
  • 161,100
  • 35
  • 287
  • 281
4

Relying on the java.version string for anything else than showing to a human is fragile and will break if running on another Java implementation.

The only reliable way programatically is to use reflection to carefully ask if a given facility is available, and then select the appropriate code accordingly.

Thorbjørn Ravn Andersen
  • 71,889
  • 31
  • 184
  • 335
  • 1
    Can you give an example of when this would fail? – Jesse Barnum Feb 26 '11 at 13:19
  • @Jesse, I'd rather put it the other way around. What rule would you set up for analyzing the java.version string? – Thorbjørn Ravn Andersen Feb 26 '11 at 14:21
  • Well, I would use java.specification.version instead of java.version, and the code would look like: If( Float.valueOf( System.getProperty("java.specification.version")) ≥= 1.6 ) {doJava6Thing}; else { doJava5Thing } – Jesse Barnum Feb 26 '11 at 19:41
  • 1
    @Jesse, I was unaware of this property. I can, however, not see from a quick look in the JLS that it is guaranteed to be present and containing a valid number. Perhaps you know where it says so? – Thorbjørn Ravn Andersen Feb 26 '11 at 20:10
  • @Jesse, also please note that by using _another_ property you agree with that it is not java.version that is the property to be analyzed. – Thorbjørn Ravn Andersen Feb 26 '11 at 20:11
  • Yes, you're correct that java.version is not the best way to determine the JDK version. The java.specification.version is documented here: http://download.oracle.com/javase/1.4.2/docs/guide/versioning/spec/versioning2.html – Jesse Barnum Feb 27 '11 at 18:51
  • 1
    @Jesse, the crucial question here if this is for Hotspot-based JVM's only. I cannot immediately tell. – Thorbjørn Ravn Andersen Feb 27 '11 at 20:07
  • 2
    Don't use `Float.valueOf` like @JesseBarnum. This failed for me because `1.8>=1.8` returned false for me, due to round-off errors. Use `.compareTo("1.8")>=0` instead. – Mark Jeronimus Feb 05 '15 at 08:42
  • @MarkJeronimus, I think your way would work, but I'd feel safer with this check: new BigDecimal( specVersion ).compareTo( new BigDecimal( "1.8" ) ) >= 0; – Jesse Barnum Feb 05 '15 at 13:50
  • I recommend against `.compareTo("1.8") >= 0` because it will fail if there's a version `11.8` or `10.1.8`. If you're going to use strings, you need to use something like `startsWith` or a regular expression. – Sarah G Mar 05 '19 at 01:42
  • As of Java 9, the java.specification.version has moved to be a single integer. – Thorbjørn Ravn Andersen Mar 05 '19 at 09:41
  • sometimes one need version just to show in stdout or in logs - and nowhere logic relies on it's value – shabunc May 16 '19 at 09:19
  • @shabunc Then you are not "Relying on the java.version string for anything else than showing to a human". – Thorbjørn Ravn Andersen May 16 '19 at 16:27
0

If you need to know the bit version(32bit or 64 bit) as well, and you are running a hotSpot JVM, you can try this code:

System.getProperty("sun.arch.data.model")

No grantee that it will work for other Java implementaions rather than hotSpot.

ZhaoGang
  • 3,933
  • 21
  • 31