How else can you fix the problem with duplicates without using the merge function in toMap?

When using Java's Stream API and the Collectors.toMap() method, if you encounter issues with duplicate keys and do not want to use a merge function, you can resolve the problem in other ways:

1. Pre-filtering or grouping:
   • Use Collectors.groupingBy() to group elements by key, then select the desired element from each group.

Map<KeyType, ValueType> map = list.stream()
    .collect(Collectors.groupingBy(
        item -> item.getKey(),
        Collectors.collectingAndThen(
            Collectors.toList(),
            listForKey -> listForKey.get(0) // select the first element
        )
    ));

2. Use distinct() or filter() before collecting:

   • Ensure there are no duplicates by key in the stream, for example, using distinct() or filtering.

3. Use toMap with LinkedHashMap and pre-sort or filter:

   • If order matters, you can first sort the stream and then use toMap with LinkedHashMap::new.

This way, you avoid an explicit merge function but require additional data processing before calling toMap().