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I want to translate a List of objects into a Map using Java 8's streams and lambdas.

This is how I would write it in Java 7 and below.

private Map<String, Choice> nameMap(List<Choice> choices)

{ final Map<String, Choice> hashMap = new HashMap<>();

for (final Choice choice : choices)

{ hashMap.put(choice.getName(), choice); }

return hashMap; }

I can accomplish this easily using Java 8 and Guava but I would like to know how to do this without Guava.

In Guava:

private Map<String, Choice> nameMap(List<Choice> choices)

{ return Maps.uniqueIndex(choices, new Function<Choice, String>()

{ @Override public String apply(final Choice input)

{ return input.getName(); } });

}

And Guava with Java 8 lambdas.

private Map<String, Choice> nameMap(List<Choice> choices) { return Maps.uniqueIndex(choices, Choice::getName);

}

1 Answer

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by (46.1k points)

To translate a List of objects into a Map using Java 8's streams and lambdas use collectors

Map<String, Choice> result =

 choices.stream().collect(Collectors.toMap(Choice::getName, 

Function.identity()));

Click here to read about the collector. 

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