MVEL allows you assign variable in your expression, either for extraction from the runtime, or for use inside the expression.

As MVEL is a dynamically typed language, you do not have to specify a type in order to declare a new variable. However, you may optionally do so.

str = "My String"; // valid
String str = "My String"; // valid

Unlike Java however, MVEL provides automatic type conversion (when possible) when assigning a value to a typed variable. For example:

String num = 1;
assert num instanceof String && num == "1";

For dynamically typed variables where you simply want to perform a type conversion, you may simply cast the value to the type you desire:

num = (String) 1;
assert num instanceof String && num == "1";

MVEL has an extensive (and pluggable) type conversion system. For more information, see: MVEL Type Conversion