What are the differences between _JAVA_OPTIONS, JAVA_TOOL_OPTIONS, and JAVA_OPTS?

Delving into the Differences between _JAVA_OPTIONS, JAVA_TOOL_OPTIONS, and JAVA_OPTS

In the realm of Java programming, setting environment variables to configure JVM arguments is a common practice. Among these options, _JAVA_OPTIONS, JAVA_TOOL_OPTIONS, and JAVA_OPTS stand out. Let's dive into their distinctions.

Background:

• JAVA_OPTS: Primarily used by third-party applications, this option is not part of the JVM.
• JAVA_TOOL_OPTIONS and _JAVA_OPTIONS: Both allow specifying JVM arguments via environment variables instead of command line parameters. They are recognized by utilities like Java and JavaC.
• Precedence: _JAVA_OPTIONS has the highest precedence, followed by command line parameters, and then JAVA_TOOL_OPTIONS.

Key Differences:

• Documentation: While JAVA_TOOL_OPTIONS has some documentation, there is none for _JAVA_OPTIONS. This suggests that _JAVA_OPTIONS may not be officially recommended.
• Usability: _JAVA_OPTIONS and JAVA_TOOL_OPTIONS are picked up even when using JVM libraries.
• Limitations: The exact limitations on the type of JVM arguments that can be included in these variables may vary depending on the specific JVM implementation.

Implementation Details:

If you're curious about the implementation details, consider checking the source code of Oracle HotSpot VM (e.g., OpenJDK7). It's worth noting that these undocumented variables may not be supported by all VMs or in future versions.

Best Practices:

• Use _JAVA_OPTIONS cautiously as it's not well-documented and may be deprecated in the future.
• Prioritize command-line arguments over environment variables for clarity and consistency.

Additional Notes:

• The precedence _JAVA_OPTIONS > command line > JAVA_TOOL_OPTIONS is important to keep in mind when setting JVM arguments.
• Setting these environment variables can be useful in scenarios where command-line arguments are not accessible, such as when launching VMs within scripts.

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