patternjavaCritical
Java 8 List<V> into Map<K, V>
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listintojavamap
Problem
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:
I can accomplish this easily using Java 8 and Guava but I would like to know how to do this without Guava.
In Guava:
And Guava with Java 8 lambdas:
This is how I would write it in Java 7 and below:
private Map nameMap(List choices) {
final Map 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 nameMap(List choices) {
return Maps.uniqueIndex(choices, new Function() {
@Override
public String apply(final Choice input) {
return input.getName();
}
});
}And Guava with Java 8 lambdas:
private Map nameMap(List choices) {
return Maps.uniqueIndex(choices, Choice::getName);
}Solution
Based on
Collectors documentation it's as simple as:Map result =
choices.stream().collect(Collectors.toMap(Choice::getName,
Function.identity()));Code Snippets
Map<String, Choice> result =
choices.stream().collect(Collectors.toMap(Choice::getName,
Function.identity()));Context
Stack Overflow Q#20363719, score: 1539
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