Shulou(Shulou.com)06/02 Report--

The JVM virtual machine provides three types of parameters: the standard parameters, including functional and output parameters, are stable and are likely to remain unchanged in future JVM releases. You can use the java command (or java-help) to retrieve all the standard parameters.

Non-standardized parameters may change in future releases. All such parameters start with-X and can be retrieved with java-X. Note that there is no guarantee that all parameters can be retrieved, and there is no-Xcomp.

Non-standardized parameters (by far the most), they are also not standard and are not even listed for a long time. In practice, however, there is no difference between the X parameter and the XX parameter. The function of the X parameter is very stable, but many of the XX parameters are still being tested (mainly the implementation of debugging and tuning JVM itself used by JVM developers).

Explain the syntax of the XX parameter in one sentence. All XX parameters start with "- XX:", but the subsequent syntax is different, depending on the type of parameter:

1) for Boolean parameters, we have "+" or "-" before setting the actual name of the JVM option.

For example,-XX:+ is used to activate the option, and-XX:- is used to log out the option.

Example:

Parameter to enable GC log:-XX:+PrintGC

2) for parameters that require non-Boolean values, such as string or integer, we first write the name of the parameter, followed by "=", and finally assign a value.

For example:-XX:MaxPermSize=2048m

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