Can you write a foreach loop like this?

[Fencer]

Say I have a List<SomeClass> and now I want to loop through the list but
I am only interested in the String representation of the SomeClass objects.

Do I have to do it like this:

for (SomeClass inst : aListOfSomeClass) {
String str = inst.toString();
// Do something with str
}

?

I don't really care about each instance objecct here, just the string
represenation of each instance, so is it possible to do something like
the following non-valid code (and here I imagine toString() being called
on each element):

for (String str : aListOfSomeClass.toString()) {
// Do something with str
}

Hope I made sense, thanks!

- Fencer

 

[Eric Sosman]

Say I have a List<SomeClass> and now I want to loop through the list but
I am only interested in the String representation of the SomeClass objects.

Do I have to do it like this:

for (SomeClass inst : aListOfSomeClass) {
String str = inst.toString();
// Do something with str
}

?

Yes. (Well, "No" if SomeClass *is* String, but ...)

The same would hold if you wanted something else derived
from the objects in the List, as opposed to the objects
themselves. The `for' will deliver the objects; you've got
to perform the desired derivation -- toString, hashCode,
getName, whatever -- on each object as you get it.

I don't really care about each instance objecct here, just the string
represenation of each instance, so is it possible to do something like
the following non-valid code (and here I imagine toString() being called
on each element):

for (String str : aListOfSomeClass.toString()) {
// Do something with str
}

No. There's no "mapcar" operation in Java.

 

[Kevin McMurtrie]

Say I have a List<SomeClass> and now I want to loop through the list but
I am only interested in the String representation of the SomeClass objects.

Do I have to do it like this:

for (SomeClass inst : aListOfSomeClass) {
String str = inst.toString();
// Do something with str
}

?

I don't really care about each instance objecct here, just the string
represenation of each instance, so is it possible to do something like
the following non-valid code (and here I imagine toString() being called
on each element):

for (String str : aListOfSomeClass.toString()) {
// Do something with str
}

Hope I made sense, thanks!

- Fencer

Java always has a hard way


public class StringItr implements Iterable<String>
{
final Iterable m_target;
public StringItr (Iterable i)
{
m_target= i;
}
public Iterator<String> iterator()
{
return new Iterator<String> ()
{
final Iterator i= m_target.iterator();
public boolean hasNext()
{
return i.hasNext();
}

public String next()
{
return String.valueOf(i.next());
}

public void remove()
{
i.remove();
}
};
}
}


....

for (String s : new StringItr(aListOfSomeClass))
....

 

[Daniel Pitts]

Java always has a hard way


public class StringItr implements Iterable<String>
{
final Iterable m_target;

 

[Kevin McMurtrie]

This should be an Iterable<?>

It should have array support, JavaDocs, and proper spacing too but it's
just free info on Usenet. I leave it to the viewer to add the finishing
touches.
[snip]

 

[Daniel Pitts]

This should be an Iterable<?>

It should have array support, JavaDocs, and proper spacing too but it's
just free info on Usenet. I leave it to the viewer to add the finishing
touches.

[snip]

Finishing touches are one thing, broken code is another ;-).
I would advocate a different approach, which is basically a library for
providing an equivalent functionality to mapcar.

 

[Arved Sandstrom]

Daniel Pitts wrote:
[ SNIP ]

Finishing touches are one thing, broken code is another ;-).
I would advocate a different approach, which is basically a library for
providing an equivalent functionality to mapcar.

If and when Java gets lambdas I'd just make "map" a method in Collection.

AHS