...
import javafx.util.Pair;
...
Pair[] testPairs = {
        new Pair<>("apple", "James"),
        new Pair<>("banana", "John"),
        new Pair<>("grapes", "Tom"),
        new Pair<>("apple", "Jenkins"),
        new Pair<>("banana", "Edward"),
        new Pair<>("grapes", "Pierre")
};

Map<String, List<String>> result1 = Arrays.stream(testPairs)...;

Map<String, String> result2 = Arrays.stream(testPairs)...;

Map<String, List<String>> result1 = Arrays.stream(testPairs)
    .collect(Collectors.groupingBy(Pair::getS,
        Collectors.mapping(Pair::getT, Collectors.toList())));

Map<String, String> result2 = Arrays.stream(testPairs)
    .collect(Collectors.toMap(Pair::getS, Pair::getT, (v1, v2) -> v1));

Map<String, List<String>> result1 = Arrays.stream(testPairs).collect(Collectors
    .groupingBy(p -> (String) p.getS(),
        Collectors.mapping(p -> (String) p.getT(), Collectors.toList())));


Map<String, String> result2 = Arrays.stream(testPairs)
    .collect(Collectors.toMap(p -> (String) p.getS(), p -> (String) p.getT(), (v1, v2) -> v1));