JIT compiler is enabled by default and it will be activated by calling a method. JIT starts at the same time as the VM, you can only modify JIT behavior at startup.
There are a number of ways to disable the JIT:
Specify -Djava.compiler=NONE on the command line.
Specify -Xint on the command line, which turns off the JIT and AOT compiler. To eliminate problems with one or the other you can turn these compilers off selectively with the -Xnojit and -Xnoaot options.
Call the java.lang.Compiler API programmatically.
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