Default Methods


Idioms and Techniques

Design Rationale

Advanced Questions

Can lambda expressions use variables from their environment?

Yes. This is called variable capture. Instance and static variables may be used and changed without restriction in the body of a lambda. The use of local variables, however, is more restricted: capture of local variables is not allowed unless they are effectively final, a concept introduced in Java 8. Informally, a local variable is effectively final if its initial value is never changed (including within the body of a lambda expression)—in other words, declaring it final would not cause a compilation failure. The concept of effective finality does not introduce any new semantics to Java; it is simply a slightly less verbose way of defining final variables. The rationale for requiring captured local variables to be effectively final is explained here.