[java] In Java 8 how do I transform a Map<K,V> to another Map<K,V> using a lambda?

If you use Guava (v11 minimum) in your project you can use Maps::transformValues.

Map<String, Column> newColumnMap = Maps.transformValues(
  originalColumnMap,
  Column::new // equivalent to: x -> new Column(x) 
)

Note: The values of this map are evaluated lazily. If the transformation is expensive you can copy the result to a new map like suggested in the Guava docs.

To avoid lazy evaluation when the returned map doesn't need to be a view, copy the returned map into a new map of your choosing.

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