Как узнать установлен ли jdk на windows

To get your jdk location in Windows, run this at a command prompt:

where java

This lists any and all locations of java.exe, including from your JAVA_HOME. For example, the 3rd line here reflects my JAVA_HOME location, where I’m pointing to JDK 8:

C:Usersme> where java
C:Program FilesCommon FilesOracleJavajavapathjava.exe
C:Program Files (x86)Common FilesOracleJavajavapathjava.exe
C:Program FilesJavajdk1.8.0_202binjava.exe

Note for comparison that java -version does not reflect my JAVA_HOME location and in fact shows java version 11 instead of 8:

C:Usersme> java -version
java version "11.0.15" 2022-04-19 LTS
Java(TM) SE Runtime Environment 18.9 (build 11.0.15+8-LTS-149)
Java HotSpot(TM) 64-Bit Server VM 18.9 (build 11.0.15+8-LTS-149, mixed mode)

This is confusing because my Java compiles (e.g., via mvn) use JDK 8 since that’s what my JAVA_HOME is pointing to. (I’m not sure whwere the 11 version came from; possibly from when I installed maven.)

Determining the difference between the JRE and JDK you’re running has never been straightforward. Seems like java -version used to be a way to do this, but no longer.

Adding to the complexity, you can also supposedly get your Java version info from Control Panel > Programs > Java > About. For me, that shows Version 8. That’s despite java -version showing version 11.0.15. And it doesn’t change even if I point my JAVA_HOME to JDK 11.

Note that this answer is also helpful. In my case, that helped me determine that I have java.exe and javac.exe at C:Program Files (x86)Common FilesOracleJavajavapath and C:Program FilesCommon FilesOracleJavajavapath. Depending on which one I have listed first in my Path variable, I get different results when i run java -version or java --version. The former seems to work when Java 8 is listed first; the latter when Java 11 is first.

A generic, pure Java solution..

For Windows and MacOS, the following can be inferred (most of the time)…

public static boolean isJDK() {
    String path = System.getProperty("sun.boot.library.path");
    if(path != null && path.contains("jdk")) {
        return true;
    }
    return false;
}

However… on Linux this isn’t as reliable… For example…

• Many JREs on Linux contain openjdk the path
• There’s no guarantee that the JRE doesn’t also contain a JDK.

So a more fail-safe approach is to check for the existence of the javac executable.

public static boolean isJDK() {
    String path = System.getProperty("sun.boot.library.path");
    if(path != null) {
        String javacPath = "";
        if(path.endsWith(File.separator + "bin")) {
            javacPath = path;
        } else {
            int libIndex = path.lastIndexOf(File.separator + "lib");
            if(libIndex > 0) {
                javacPath = path.substring(0, libIndex) + File.separator + "bin";
            }
        }
        if(!javacPath.isEmpty()) {
            return new File(javacPath, "javac").exists() || new File(javacPath, "javac.exe").exists();
        }
    }
    return false;
}

Warning: This will still fail for JRE + JDK combos which report the JRE’s sun.boot.library.path identically between the JRE and the JDK. For example, Fedora’s JDK will fail (or pass depending on how you look at it) when the above code is run. See unit tests below for more info…

Unit tests:

# Unix
java -XshowSettings:properties -version 2>&1|grep "sun.boot.library.path"
# Windows
java -XshowSettings:properties -version 2>&1|find "sun.boot.library.path"

    # PASS: MacOS AdoptOpenJDK JDK11
    /Library/Java/JavaVirtualMachines/adoptopenjdk-11.jdk/Contents/Home/lib

    # PASS: Windows Oracle JDK12
    c:Program FilesJavajdk-12.0.2bin

    # PASS: Windows Oracle JRE8
    C:Program FilesJavajre1.8.0_181bin

    # PASS: Windows Oracle JDK8
    C:Program FilesJavajdk1.8.0_181bin

    # PASS: Ubuntu AdoptOpenJDK JDK11
    /usr/lib/jvm/adoptopenjdk-11-hotspot-amd64/lib

    # PASS: Ubuntu Oracle JDK11
    /usr/lib/jvm/java-11-oracle/lib

    # PASS: Fedora OpenJDK JDK8
    /usr/lib/jvm/java-1.8.0-openjdk-1.8.0.141-1.b16.fc24.x86_64/jre/lib/amd64

    #### FAIL: Fedora OpenJDK JDK8
    /usr/java/jdk1.8.0_231-amd64/jre/lib/amd64

A generic, pure Java solution..

For Windows and MacOS, the following can be inferred (most of the time)…

public static boolean isJDK() {
    String path = System.getProperty("sun.boot.library.path");
    if(path != null && path.contains("jdk")) {
        return true;
    }
    return false;
}

However… on Linux this isn’t as reliable… For example…

• Many JREs on Linux contain openjdk the path
• There’s no guarantee that the JRE doesn’t also contain a JDK.

So a more fail-safe approach is to check for the existence of the javac executable.

public static boolean isJDK() {
    String path = System.getProperty("sun.boot.library.path");
    if(path != null) {
        String javacPath = "";
        if(path.endsWith(File.separator + "bin")) {
            javacPath = path;
        } else {
            int libIndex = path.lastIndexOf(File.separator + "lib");
            if(libIndex > 0) {
                javacPath = path.substring(0, libIndex) + File.separator + "bin";
            }
        }
        if(!javacPath.isEmpty()) {
            return new File(javacPath, "javac").exists() || new File(javacPath, "javac.exe").exists();
        }
    }
    return false;
}

Warning: This will still fail for JRE + JDK combos which report the JRE’s sun.boot.library.path identically between the JRE and the JDK. For example, Fedora’s JDK will fail (or pass depending on how you look at it) when the above code is run. See unit tests below for more info…

Unit tests:

# Unix
java -XshowSettings:properties -version 2>&1|grep "sun.boot.library.path"
# Windows
java -XshowSettings:properties -version 2>&1|find "sun.boot.library.path"

    # PASS: MacOS AdoptOpenJDK JDK11
    /Library/Java/JavaVirtualMachines/adoptopenjdk-11.jdk/Contents/Home/lib

    # PASS: Windows Oracle JDK12
    c:Program FilesJavajdk-12.0.2bin

    # PASS: Windows Oracle JRE8
    C:Program FilesJavajre1.8.0_181bin

    # PASS: Windows Oracle JDK8
    C:Program FilesJavajdk1.8.0_181bin

    # PASS: Ubuntu AdoptOpenJDK JDK11
    /usr/lib/jvm/adoptopenjdk-11-hotspot-amd64/lib

    # PASS: Ubuntu Oracle JDK11
    /usr/lib/jvm/java-11-oracle/lib

    # PASS: Fedora OpenJDK JDK8
    /usr/lib/jvm/java-1.8.0-openjdk-1.8.0.141-1.b16.fc24.x86_64/jre/lib/amd64

    #### FAIL: Fedora OpenJDK JDK8
    /usr/java/jdk1.8.0_231-amd64/jre/lib/amd64

Установка JDK

JDK (Java Development Kit) — это комплект разработки для JVM-платформы, включающий в себя Java-компилятор, стандартные библиотеки, различные утилиты, а также среду выполнения JRE (Java Runtime Environment). Наличие установленной JDK обязательно для ведения разработки на Scala (как и на любом другом JVM-языке).

Как проверить, установлена ли JDK?

Если Вы уже запускали Java-приложения на своем компьютере, то с наибольшей вероятностью у Вас имеется установленная JRE.

Наличие JRE не обязательно означает, что у Вас есть JDK.

1. Проверьте версию JRE:

• java -version

  java version "1.6.0_37"
  Java(TM) SE Runtime Environment (build 1.6.0_37-b06-434-11M3909)
  Java HotSpot(TM) 64-Bit Server VM (build 20.12-b01-434, mixed mode)

• Последние цифры версий, номера сборок, а также разрядность и архитектура в приведенных примерах могут отличаться от значений на Вашей платформе.

2. Проверьте версию компилятора:

javac -version

javac 1.6.0_37

3. Найдите каталог инсталляции JDK. Проверьте следующие стандартные пути в соответствие с Вашей операционной системой (номера версий могут отличаться):

• Windows C:Program FilesJavajdk1.6.0_30
• Linux /usr/lib/jvm/jdk1.6.0_30
• Mac OS X /System/Library/Frameworks/JavaVM.framework/Home

4. Убедитесь, что переменная окружения JAVA_HOME указывает на каталог инсталляции, а также что путь к $JAVA_HOME/bin (%JAVA_HOME%bin) включен в переменную окружения PATH.

Если какой-либо из пунктов вызывает у Вас проблемы, пожалуйста, прочитайте еще раз введение к курсу IT1205: Программирование Java SE, где подробно описан процесс корректрой установки JDK.