transform.java

import java.util.function.Function;
import java.util.*;
import java.util.stream.*;

static <X, Y, Z> Map<X, Z> transform(Map<? extends X, ? extends Y> input,
                                     Function<Y, Z> function) {
    return input.keySet().stream()
            .collect(Collectors.toMap(Function.identity(),
                    key -> function.apply(input.get(key))));
}


// Example Usage:
Map<String, String> input = new HashMap<String, String>();

input.put("foo", "10");
input.put("bar", "10");

Map<String, Integer> output = transform(input,
            (val) -> Integer.parseInt(val));