Can lambda expressions in Java access local variables?

Lambda expressions in Java can access local variables from the enclosing scope, but those variables must be effectively final. This means that the variables cannot be modified after they are assigned. Here is an example:

int factor = 2; Function<Integer, Integer> multiply = (Integer x) -> x * factor; int result = multiply.apply(5);  // result is 10

In this example, the lambda expression multiplies its input by the factor variable, which is effectively final. If the factor variable were modified after being captured by the lambda, it would result in a compile-time error. This restriction ensures that the behavior of the lambda expression remains consistent and predictable.

This design choice in Java is intended to prevent issues related to variable mutation, which can lead to bugs and unpredictable behavior in multithreaded or complex code. By enforcing the “effectively final” rule, Java helps developers write safer and more reliable code when using lambda expressions.