How to convert the following nested forEach loop into functional code?

ABC abc = new ABC();

for (A a : aList) {
    for (String b : bList) {
        if (Objects.equals(a.getName(), b)) {
            abc.setId(a.getId());
            abc.setValue(a.getValue());
        }
    }
}

I've tried to convert it this way, but it didn't work:

aList.forEach(a -> {
    bList.stream()
         .filter(b -> Objects.equals(b, a.getName()));

    abc.setId(a.getId());
    abc.setValue(a.getValue());
});

CodePudding user response：

You can try

aList.forEach(a -> {
    if( bList.stream()
         .anyMatch(b -> Objects.equals(b, a.getName()))){

       abc.setId(a.getId());
       abc.setValue(a.getValue());
    }
});

or better

aList.stream().filter(a -> bList.stream()
                                .anyMatch(b -> Objects.equals(b,a.getName())))
              .findAny()
              .ifPresent(a -> {
                  abc.setId(a.getId());
                  abc.setValue(a.getValue());
               });

CodePudding user response：

Not sure what is considered a "functional code" and why that is needed here.
My approach, assuming bList is a List<String>:

var abc = aList
          .stream()
          .filter(this::isKnownName)
          .map(this::abcFromA)
          .findFirst()    // see ¹ bellow 
          .orElseGet(ABC::new);

using the following helper functions - not really needed, we could use lambda expressions, but I think using this is a little bit more readable ² :

private boolean isKnownName(A a) {
    return bList.contains(a.getName());
}
    
private ABC abcFromA(A a) {
    var result = new ABC();
    result.setId(a.getId());
    result.setValue(a.getValue());
    return result;
}

¹ this code is using the first match found in bList, code in question is using the last match

² I would struggle between using this solution at all and using a single loop (with bList.contains() instead of inner loop as posted in question).