2 arrays to map in Java. Values array may contain null elements [duplicate]

Question

I have 2 arrays (same size) String[] and Object[]. The question: is there a more elegant way to convert them to Map than this?

private Map<String, Object> arraysToMap(String[] keys, Object[] values) {
    Map<String, Object> map = new HashMap<>();
    if (keys.length != 0) {
        for (int i = 0; i < keys.length; i++) {
            map.put(keys[i], values[i]);
        }
    }
    return map;
}

Java 8 style maybe?

Important notes:

values may contain null value
keys contains non-null unique elements

make sure that the sizes are equal, otherwise you might get a ArrayIndexOutOfBoundsException — Andrew
– Andrew, Commented Dec 28, 2017 at 16:08

Alex Mamo · Accepted Answer · 2017-12-28 16:47:45Z

1

To solve this, you can use the following code:

public class Test {
    static String[] keys = {"String1", "String2"};
    static Object[] values = {new Object(), new Object()};

    public static void main(String[] args) {
        Map<String, Object> map = IntStream.range(0, keys.length)
                .boxed()
                .collect(Collectors.toMap(i -> keys[i], i -> values[i]));
    }
}

As can you see first I have created a range from zero to keys.length, then we have replaced the primitive values of the stream with their corresponding object wrapper classes. At the end we used Collectors.toMap method to actually create the map. Also make sure that the sizes to be equal.

edited Dec 28, 2017 at 16:47

answered Dec 28, 2017 at 16:07

Alex Mamo

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22 Comments

Lenar Over a year ago

There is a problem. That fails with NPE if one of values is null.

Alex Mamo Over a year ago

This was happening because the array were not initialized. It was an example but please see my updated answer.

Nikolai Shevchenko Over a year ago

Map itself supports null values but overridden merge() method from HashMap does not.

@Override     public V merge(K key, V value,                    BiFunction<? super V, ? super V, ? extends V> remappingFunction) {         if (value == null)             throw new NullPointerException();

Nikolai Shevchenko Over a year ago

@AlexMamo you example can be extended with "dirty hack" :) Following code will work because Hashtable's merge() implementation accepts null values

Map<String, Object> map = IntStream.range(0, keys.length)                 .boxed()                 .collect(Collectors.toMap(i -> keys[i], i -> values[i], (v1, v2) -> v1, Hashtable::new));         Map<String, Object> result = new HashMap<>(map);

Eugene Over a year ago

@NikolayShevchenko right, I should have made myself more clear. what I meant is that you can build a custom collector and provide the merge function as you want (if one is needed)

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