How does Java's switch work under the hood?

Question

How does Java\'s switch statement work under the hood? How does it compare the value of the variable being used, to those given in the case parts? Does it use ==

Answer 1

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In bytecode there are two forms of switch: tableswitch and lookupswitch. One assumes a dense set of keys, the other sparse. See the description of compiling switch in the JVM spec. For enums, the ordinal is found and then the code continues as the int case. I am not entirely sure how the proposed switch on String little feature in JDK7 will be implemented.

However, heavily used code is typically compiled in any sensible JVM. The optimiser is not entirely stupid. Don't worry about it, and follow the usual heuristics for optimisation.

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