Newbie: iterating two collections

[usgog]

I have two ArrayLists: List<Boolean> A and List<T> B with same size. I
want something like
for (int i =0; i < A.size(); i++) { B.booleanValue =
A.booleanValue); }. Just one to one value set. I am pretty new to
iterators. Can I use foreach in java for that? Any decent approach
instead of nested loops?

 

[heysc0tt]

I have two ArrayLists: List<Boolean> A and List<T> B with same size. I
want something like
for (int i =0; i < A.size(); i++) { B.booleanValue =
A.booleanValue); }. Just one to one value set. I am pretty new to
iterators. Can I use foreach in java for that? Any decent approach
instead of nested loops?

Ok so what I understand you want is an iterator that will set all
boolean values in list B to be the same as list A. I am assuming the
type of list B (T) is actually Boolean, if not you can change the
setter. As far as the iterator, you were close.

Here is a simple example:

for(int i; i<A.size(); i++)
{
B.set(i, A.get(i));
}

This assumes the List B is already has elements which you're replacing
with the elements in A. If List B is empty you could just use the add
method instead:

for(int i; i<A.size(); i++)
{
B.add(A.get(i));
}

Scott

 

[Mark Jeffcoat]

I have two ArrayLists: List<Boolean> A and List<T> B with same size. I
want something like
for (int i =0; i < A.size(); i++) { B.booleanValue =
A.booleanValue); }. Just one to one value set. I am pretty new to
iterators. Can I use foreach in java for that? Any decent approach
instead of nested loops?

If I've understood you correctly, this is one of those
times when the new iterator syntax is a bit awkward. What
you wrote almost works. (The booleanValue bit is not valid syntax,
though. It's a method call (or should be), and you can't assign to it.)

public T someMethod(Boolean b) { .... }

List<Boolean> a = ...;
List<T> b = ... ;

assert(a.size() == b.size());
for (int i=0; i<a.size(); ++i) {
b.set(i, someMethod(a.get(i)));
}

Fill in the blanks as makes you happy. Get() and set() are
specific to Lists; you will need Iterators for more general
Collections.

 

[tej]

Hi all
i am working on java platform
i ve to parese a textfile containing Japanese charaters can any body
help in this problem

Thanks& Regards
Tej

 

[Thomas Hawtin]

I have two ArrayLists: List<Boolean> A and List<T> B with same size. I
want something like
for (int i =0; i < A.size(); i++) { B.booleanValue =
A.booleanValue); }. Just one to one value set. I am pretty new to
iterators. Can I use foreach in java for that? Any decent approach
instead of nested loops?

A few points:

Variables should start with a lower case letter.

Boolean is immutable. You cannot change the actual object, but you can
change references to a Boolean (so long as the references are not final).

It's a good idea to avoid non-private fields.

You need to specify that T is of some concrete type with the members
that your code requires. In this example you can use wildcards.

It's probably better to use the original list, rather than having two
copies of the same thing.

Instead of List<Boolean> you may find BitSet preferable, particularly as
it will be around 32 or 64 times as compact (depending on whether your
JVM is using 32 or 64 bit addresses).

If you start with 'A' as an empty List, you don't need to worry about an
iterator for it.


So, ignoring the BitSet and using a single List:

interface BooleanThing {
boolean isBooleanValue();
}

public static List<Boolean> extractBooleans(
Iterable<? extends BooleanThing> things
) {
List<Boolean> booleans = new ArrayList<Boolean>(objects.size());
for (BooleanThing thing : things) {
booleans.add(thing.isBooleanValue());
}
return booleans;
}

Obviously the names aren't very good as I don't know why you are doing this.

Tom Hawtin

 

[Michael Rauscher]

Hi all
i am working on java platform
i ve to parese a textfile containing Japanese charaters can any body
help in this problem

Wrong thread but: text files are binary files, too.

The first thing you need to know: which encoding was used to generate
that file?

The second thing: does Java support this encoding out of the box? If e.
g. the file is UTF-16 encoded, then: yes.

The last thing: create an InputStreamReader that uses the encoding.

So, e. g. to read an UTF-16 encoded file:

BufferedReader reader = new BufferedReader( new InputStreamReader(
new FileInputStream("myfile.txt"), "UTF-16") );

Bye
Michael