crmepham :
Currently I have to define different methods based on the type of the Function
I want to pass into the method, e.g:
addCustomParameter(orderLinePrefix + "quantity=", concatenateLong(orderLines, OrderPart::getQuantity));
addCustomParameter(orderLinePrefix + "surcharge=", concatenateDouble(orderLines, OrderPart::getSurcharge));
addCustomParameter(orderLinePrefix + "dropship=", concatenateBoolean(orderLines, OrderPart::isDropship));
The methods look like this:
@Nonnull
public <T> String concatenateBoolean(@Nonnull final Collection<T> items, @Nonnull final Function<T, Boolean> mapper)
{
return items.stream()
.map(mapper)
.map(String::valueOf)
.collect(joining(","));
}
@Nonnull
public <T> String concatenateLong(@Nonnull final Collection<T> items, @Nonnull final Function<T, Long> mapper)
{
return items.stream()
.map(mapper)
.map(String::valueOf)
.collect(joining(","));
}
@Nonnull
public <T> String concatenateDouble(@Nonnull final Collection<T> items, @Nonnull final Function<T, Double> mapper)
{
return items.stream()
.map(mapper)
.map(String::valueOf)
.collect(joining(","));
}
How can I refactor the above 3 methods into a single method that will accept any type and return a String?
Andy Turner :
Use a wildcard return type for the mapper:
@Nonnull
public <T> String concatenateAny(@Nonnull final Collection<T> items, @Nonnull final Function<? super T, ?> mapper)
{
return items.stream()
.map(mapper)
.map(String::valueOf)
.collect(joining(","));
}