Java: How do I assign the first value in a for loop to the variable?

Question

I have a List of type Info with member fields String and Map<String, Set<String>> . I need to iterate over the Set<String> s. Is it possible for me to assign the first Set<String> to a variable and perform operations on itself and the remaining values of each key ?

I'm new to Java, so this may not be properly articulated.

What I've tried. Given my scenario is understood, is using entrySet() correct here or will info.getInfoMap.values() suffice?

for (Info info : listOfInfo) {

      for (Map.Entry<String, Set<String>> entry : info.getInfoMap().entrySet()) {

        final Set<String> firstSetValue = entry.getValue();
        Set<String> set = entry.getValue();

        // do something to remaining sets with the first set
        // firstSetValue.equals(set)
        // firstSetValue.containsAll(set)


      }

Answer 1

Assuming those sets can't be null (and using var which is something you pretty much always want to use when iterating over entrySets):

Set<String> firstSet = null;

for (Info info : listOfInfo) {
   for (var entry : info.getInfoMap().entrySet()) {
       if (firstSet == null) firstSet = entry.getValue();
       // more here
    }
}

your code doesn't work: That firstSetValue = line is executed every loop. Making it final changes nothing: Variables in java spring into existence when you declare them and poof away when their 'scope' runs out, and java is scoped to the nearest {} . In other words, when the inner for loop loops, a new firstSetVariable poofs into existence, and then at the } that marks the end of the loop, it poofs away, and then assuming the loop loops once more, poof, there is an entirely new firstSetVariable . Thus, they don't 'remember' the first value, as they are entirely new, and marking them final makes no difference (it works fine: Their value indeed never changes, so they can be marked final. Instead the entire variable poofs out and back into existence every loop).

Answer 2

You just need to store the variable outside of the loop. Two approaches that immediately come to mind:

Set<Map.Entry<String, Set<String>> entrySet = info.getInfoMap().getEntrySet();
final Set<String> first = entrySet.iterator().next();

for (final Map.Entry<String, Set<String>> entry : entrySet) {
   ...
}

or

Set<String> first = null;

for (final Map.Entry<String, Set<String>> entry : info.getInfoMap().getEntrySet()) {
    if (first == null) {
        first = entry.getValue();
    }

    ...
}