Is it possible to create variables at runtime in Java?

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Is it possible to create variables at runtime in Java?

The simple answer is No.

Java is a static language and does not support the injection of new variable declarations into an existing compiled program. There are alternatives (in order of decreasing usefulness / increasing difficulty):

  • Represent your “variables” as name / value pairs in a Map. Or come up with some other design that doesn’t require real dynamic variables.
  • Use a scripting language that runs on the JVM and is callable from Java.
  • Use some kind of templating mechanism to generate new source code containing the declarations, and compile and load it dynamically.
  • Use a byte code manipulation library (e.g. BCEL) to create class files on the fly and then dynamically load them.

The first approach is the best. Java is a static language, and works best if you don’t fight it. If this is a problem for you, maybe you are using the wrong language.

The last two are difficult / complicated and have significant performance costs. They are almost certainly not going to help …

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