Java Map<String, MyObject> to Map<String, String>

Question

I have a Map and I want to convert it to Map. The keys from the first Map will be equal to the ones in the second. MyObject has a property that I want to use as the value for the second map. So what I have now is a for loop that does:

for (Map.Entry<String, MyObject> entry : originalMap.getTextMessages().entrySet()) {
  newMap.put(entry.getKey(), entry.getValue().getStringValue());
}

Now I've got the feeling it could be easier... can anyone shed a light on this? We're using Java 7 by the way but if you have some clever Java 8 function for this, please share it too.

This is 3 lines of code... what's not easy about this?

ControlAltDel
– ControlAltDel

2015-11-02 11:54:29 +00:00
Commented Nov 2, 2015 at 11:54 — ControlAltDel
– ControlAltDel, Commented Nov 2, 2015 at 11:54
With Java 7 I think that is the easiest way.

Paul Boddington
– Paul Boddington

2015-11-02 11:55:41 +00:00
Commented Nov 2, 2015 at 11:55 — Paul Boddington
– Paul Boddington, Commented Nov 2, 2015 at 11:55

Eran · Accepted Answer · 2015-11-02 11:55:38Z

3

It's quite straight forward with Java 8 Streams :

Map<String,String> newMap = 
    originalMap.entrySet().stream().collect(Collectors.toMap(e->e.getKey(),e->e.getValue().getStringValue()));

In Java 7 I think you can't do it with less code than you already have.

answered Nov 2, 2015 at 11:55

Eran

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Comments

Mena · Accepted Answer · 2015-11-02 11:59:29Z

0

Here's another Java 8 example with streams and a BiConsumer, all in a main method:

public static void main(String[] args) throws Exception {
    class MyObject {
        String s;
        MyObject(String s) {
            this.s = s;
        }
        String getStringValue() {
            return s;
        }
    }
    Map<String, MyObject> original = new HashMap<String, MyObject>();
    original.put("original", new MyObject("0"));
    Map<String, String> converted = new HashMap<String, String>();
    // iterates each entry and puts the conversion in the new map
    original.forEach((s,m) -> {converted.put(s, m.getStringValue());});
    System.out.println(converted);
}

Output

{original=0}

answered Nov 2, 2015 at 11:59

Mena

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2 Comments

ControlAltDel Over a year ago

This to me is definitely more complicated than the original

Mena Over a year ago

@ControlAltDel consider the only relevant line here is the forEach. The rest is just setting up and context.

jctim · Accepted Answer · 2015-11-02 12:23:40Z

0

In Java7 you can do it with help of Apache commons collections:

import org.apache.commons.collections4.MapUtils;

Map<String, String> newMap = MapUtils.transformedMap(originalMap, TransformerUtils.<String>nopTransformer(), new Transformer<Object, String>() {
        @Override
        public String transform(final Object objectValue) {
            return objectValue.toString();
        }
    });

answered Nov 2, 2015 at 12:23

jctim

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Comments

jinsihou · Accepted Answer · 2019-07-16 02:04:22Z

0

you can do it with help of guava:

import org.guava.collect.Maps;

Map<String, String> newMap = Maps.transformEntries(oldMap, new Maps.EntryTransformer<String, Object, String>() {
            @Override
            public String transformEntry(@Nullable String key, @Nullable Object value) {
                return value == null ? null : value.toString();
            }
        });

answered Jul 16, 2019 at 2:04

jinsihou

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