Java lambda - for loop counter is not effectively final
for-loop, java, java-8, lambda
Solution
TLDR: `i` is not `final` because it is modified (`i++`) at each iteration of the `for` loop.
why i is not effectively final inside the scope of the for loop ?
The `for` loop syntax is
for (initialization; termination; increment) {
statement(s)
}
The increment expression is invoked after each iteration through the loop. In your case, increment is `i++` so `i` is modified after each iteration.
You could confirm this by declaring `i` final:
for (final int i = 0; i < x.getBooks().size(); i++) {
}
you will get this compilation error:
The final local variable i cannot be assigned.
It must be blank and not using a compound assignment
is this the simplest workaround ?
In the case of a `for` loop: yes.
But you could use a `while` loop as shown by @dkatzel or a `foreach`:
int i = 0;
for (Book book: x.getBooks()) {
int i2 = i;
...
i++;
}
Problem
Given this situation where a lambda is inside a for loop I would expect the counter i to be effectively final. The compiler complains that i is not effectively final so I had to use i2. ``` for (int i = 0; i < x.getBooks().size(); i++){ //The compiler needs i to be effectively final. int i2 = i; List<Book> books = bookstore.stream() .filter(c -> c.getAuthors().get(i2).equals("xxx")) .collect(Collectors.toList()); } ``` So the question is why i is not effectively final inside the scope of the for loop and is this the simplest workaround.