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Q: Why are there no global variables in Java?

JavaFAQ Home » Java IAQ by Peter Norvig Go to all tips in Java IAQ by Peter Norvig


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Q: Why are there no global variables in Java?

Answer: Global variables are considered bad form for a variety of reasons:
  • Adding state variables breaks referential transparency (you no longer can understand a statement or expression on its own: you need to understand it in the context of the settings of the global variables).
  • State variables lessen the cohesion of a program: you need to know more to understand how something works. A major point of Object-Oriented programming is to break up global state into more easily understood collections of local state.
  • When you add one variable, you limit the use of your program to one instance. What you thought was global, someone else might think of as local: they may want to run two copies of your program at once.
For these reasons, Java decided to ban global variables.

This tip is reprinted on JavaFAQ.nu by by courtesy of Peter Norvig I am thankful for his important contributions to my site - 21 Infrequently Answered Java Questions. Alexandre Patchine


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