Does Java have global variables?

In Java, is there any performance benefit gained from making local variables final?

• I've heard contradicting views whether there can be any performance gained by making local variables final in Java. Or by creating a final local variable that references a member variable. Can anyone provide a clear answer to this? (assuming Java 6/7 and a standard JVM such as Oracle's).

• Answer:

  Accessing a local variable is faster than accessing a field.  It's best to keep field accesses out of performance-critical inner loops when possible.  (Profile first, of course, to see if it matters.)  In theory the JVM could "inline" the field to a local variable automatically under the right conditions, but don't count on it. A final local variable is not any different from a normal local variable at runtime.  The "final" keyword on a local variable expresses a constraint on the source code (that it is assigned to once) which the compiler can easily check. Final *fields* do allow additional optimizations, and static final fields with primitive values (as in "public static final int MY_CONSTANT = 3") are treated as compile-time constants and inlined.