In Java 8 how do I transform a Map to another Map using a lambda?

Question

I\'ve just started looking at Java 8 and to try out lambdas I thought I\'d try to rewrite a very simple thing I wrote recently. I need to turn a Map of String to Column int

Answer 1

You could use a Collector:

import java.util.*;
import java.util.stream.Collectors;

public class Defensive {

  public static void main(String[] args) {
    Map original = new HashMap<>();
    original.put("foo", new Column());
    original.put("bar", new Column());

    Map copy = original.entrySet()
        .stream()
        .collect(Collectors.toMap(Map.Entry::getKey,
                                  e -> new Column(e.getValue())));

    System.out.println(original);
    System.out.println(copy);
  }

  static class Column {
    public Column() {}
    public Column(Column c) {}
  }
}