Getting version of java in runtime

Question

I need to write version-independent java code, because of some bugs in JDK 1.5 which was fixed in JDK 1.6 now i use the following condition:

if (System.getProperty("java.version").startsWith("1.5.")) {
...
} else{
...
}

Is there another possibility to check this? Will it work for JVM from IBM?

Answer 1

java.version is a standard property which exists in every VM.

There is just a tiny trick which might make your life easier: Search for the second dot and cut the string there. Then convert it to double. Now, you can check the version much more comfortably:

if (version >= 1.5) ...

You can put this into static code of a class so it runs only once:

public static double JAVA_VERSION = getVersion ();

static double getVersion () {
    String version = System.getProperty("java.version");
    int pos = 0, count = 0;
    for ( ; pos<version.length() && count < 2; pos ++) {
        if (version.charAt(pos) == '.') count ++;
    }
    return Double.parseDouble (version.substring (0, pos));
}

Answer 2

Don't know another way of checking this, but this: http://java.sun.com/j2se/1.5.0/docs/api/java/lang/System.html#getProperties()" implies "java.version" is a standard system property so I'd expect it to work with other JVMs.

Answer 3

These articles seem to suggest that checking for 1.5 or 1.6 prefix should work, as it follows proper version naming convention.

Sun Technical Articles

• J2SE SDK/JRE Version String Naming Convention
• Version 1.5.0 or 5.0?
  • "J2SE also keeps the version number 1.5.0 (or 1.5) in some places that are visible only to developers, or where the version number is parsed by programs"
    • "java.version system property"
• Version 1.6.0 Used by Developers
  • "Java SE keeps the version number 1.6.0 (or 1.6) in some places that are visible only to developers, or where the version number is parsed by programs."
    • "java.version system property"