[java] How can I tell if I'm running in 64-bit JVM or 32-bit JVM (from within a program)?

How can I tell if the JVM in which my application runs is 32 bit or 64-bit? Specifically, what functions or properties I can used to detect this within the program?

Under Windows 7 in the "Control Panel" under "Programs | Programs and Features" the 64-bit variants of JRE & JDK are listed with "64-bit" in parentheses (e.g. "Java SE Development Kit 7 Update 65 (64-Bit)"), while for the 32-bit variants the variant is not mentioned in parentheses (e.g. just "Java SE Development Kit 8 Update 60").

This is the way JNA solves this with Platform.is64Bit() (https://github.com/java-native-access/jna/blob/master/src/com/sun/jna/Platform.java)

 public static final boolean is64Bit() {
        String model = System.getProperty("sun.arch.data.model",
                                          System.getProperty("com.ibm.vm.bitmode"));
        if (model != null) {
            return "64".equals(model);
        }
        if ("x86-64".equals(ARCH)
            || "ia64".equals(ARCH)
            || "ppc64".equals(ARCH) || "ppc64le".equals(ARCH)
            || "sparcv9".equals(ARCH)
            || "mips64".equals(ARCH) || "mips64el".equals(ARCH)
            || "amd64".equals(ARCH)
            || "aarch64".equals(ARCH)) {
            return true;
        }
        return Native.POINTER_SIZE == 8;
}

ARCH = getCanonicalArchitecture(System.getProperty("os.arch"), osType);

static String getCanonicalArchitecture(String arch, int platform) {
        arch = arch.toLowerCase().trim();
        if ("powerpc".equals(arch)) {
            arch = "ppc";
        }
        else if ("powerpc64".equals(arch)) {
            arch = "ppc64";
        }
        else if ("i386".equals(arch) || "i686".equals(arch)) {
            arch = "x86";
        }
        else if ("x86_64".equals(arch) || "amd64".equals(arch)) {
            arch = "x86-64";
        }
        // Work around OpenJDK mis-reporting os.arch
        // https://bugs.openjdk.java.net/browse/JDK-8073139
        if ("ppc64".equals(arch) && "little".equals(System.getProperty("sun.cpu.endian"))) {
            arch = "ppc64le";
        }
        // Map arm to armel if the binary is running as softfloat build
        if("arm".equals(arch) && platform == Platform.LINUX && isSoftFloat()) {
            arch = "armel";
        }

        return arch;
    }

static {
        String osName = System.getProperty("os.name");
        if (osName.startsWith("Linux")) {
            if ("dalvik".equals(System.getProperty("java.vm.name").toLowerCase())) {
                osType = ANDROID;
                // Native libraries on android must be bundled with the APK
                System.setProperty("jna.nounpack", "true");
            }
            else {
                osType = LINUX;
            }
        }
        else if (osName.startsWith("AIX")) {
            osType = AIX;
        }
        else if (osName.startsWith("Mac") || osName.startsWith("Darwin")) {
            osType = MAC;
        }
        else if (osName.startsWith("Windows CE")) {
            osType = WINDOWSCE;
        }
        else if (osName.startsWith("Windows")) {
            osType = WINDOWS;
        }
        else if (osName.startsWith("Solaris") || osName.startsWith("SunOS")) {
            osType = SOLARIS;
        }
        else if (osName.startsWith("FreeBSD")) {
            osType = FREEBSD;
        }
        else if (osName.startsWith("OpenBSD")) {
            osType = OPENBSD;
        }
        else if (osName.equalsIgnoreCase("gnu")) {
            osType = GNU;
        }
        else if (osName.equalsIgnoreCase("gnu/kfreebsd")) {
            osType = KFREEBSD;
        }
        else if (osName.equalsIgnoreCase("netbsd")) {
            osType = NETBSD;
        }
        else {
            osType = UNSPECIFIED;
        }
}

Complementary info:

On a running process you may use (at least with some recent Sun JDK5/6 versions):

$ /opt/java1.5/bin/jinfo -sysprops 14680 | grep sun.arch.data.model
Attaching to process ID 14680, please wait...
Debugger attached successfully.
Server compiler detected.
JVM version is 1.5.0_16-b02
sun.arch.data.model = 32

where 14680 is PID of jvm running the application. "os.arch" works too.

Also other scenarios are supported:

jinfo [ option ] pid
jinfo [ option ] executable core
jinfo [ option ] [server-id@]remote-hostname-or-IP 

However consider also this note:

"NOTE - This utility is unsupported and may or may not be available in future versions of the JDK. In Windows Systems where dbgent.dll is not present, 'Debugging Tools for Windows' needs to be installed to have these tools working. Also the PATH environment variable should contain the location of jvm.dll used by the target process or the location from which the Crash Dump file was produced."

For Windows, you can check the Java home location. If it contains (x86) it is 32-bit otherwise 64-bit:

public static boolean is32Bit()
{
    val javaHome = System.getProperty("java.home");
    return javaHome.contains("(x86)");
}

public static boolean is64Bit()
{
    return !is32Bit();
}

Example paths:

C:\Program Files (x86)\Java\jdk1.8.0_181\bin\java.exe # 32-bit
C:\Program Files\Java\jdk-10.0.2\bin\java.exe # 64-bit

Why care about a Windows only solution?

If you need to know which bit version you're running on, you're likely fiddling around with native code on Windows so platform-independence is out of the window anyway.

I installed 32-bit JVM and retried it again, looks like the following does tell you JVM bitness, not OS arch:

System.getProperty("os.arch");
#
# on a 64-bit Linux box:
# "x86" when using 32-bit JVM
# "amd64" when using 64-bit JVM

This was tested against both SUN and IBM JVM (32 and 64-bit). Clearly, the system property is not just the operating system arch.

Just type java -version in your console.

If a 64 bit version is running, you'll get a message like:

java version "1.6.0_18"
Java(TM) SE Runtime Environment (build 1.6.0_18-b07)
Java HotSpot(TM) 64-Bit Server VM (build 16.0-b13, mixed mode)

A 32 bit version will show something similar to:

java version "1.6.0_41"
Java(TM) SE Runtime Environment (build 1.6.0_41-b02)
Java HotSpot(TM) Client VM (build 20.14-b01, mixed mode, sharing)

Note Client instead of 64-Bit Server in the third line. The Client/Server part is irrelevant, it's the absence of the 64-Bit that matters.

If multiple Java versions are installed on your system, navigate to the /bin folder of the Java version you want to check, and type java -version there.

If you are using JNA, you can check whether com.sun.jna.Native.POINTER_SIZE == 4 (32 bit) or com.sun.jna.Native.POINTER_SIZE == 8 (64 bit).

To get the version of JVM currently running the program

System.out.println(Runtime.class.getPackage().getImplementationVersion());

If you're using JNA, you can do thisPlatform.is64Bit().

For certain versions of Java, you can check the bitness of the JVM from the command line with the flags -d32 and -d64.

$ java -help
...
    -d32          use a 32-bit data model if available
    -d64          use a 64-bit data model if available

To check for a 64-bit JVM, run:

$ java -d64 -version

If it's not a 64-bit JVM, you'll get this:

Error: This Java instance does not support a 64-bit JVM.
Please install the desired version.

Similarly, to check for a 32-bit JVM, run:

$ java -d32 -version

If it's not a 32-bit JVM, you'll get this:

Error: This Java instance does not support a 32-bit JVM.
Please install the desired version.

These flags were added in Java 7, deprecated in Java 9, removed in Java 10, and no longer available on modern versions of Java.

On Linux, you can get ELF header information by using either of the following two commands:

file {YOUR_JRE_LOCATION_HERE}/bin/java

o/p: ELF 64-bit LSB executable, AMD x86-64, version 1 (SYSV), for GNU/Linux 2.4.0, dynamically linked (uses shared libs), for GNU/Linux 2.4.0, not stripped

or

readelf -h {YOUR_JRE_LOCATION_HERE}/bin/java | grep 'Class'

o/p: Class: ELF64