Limit in For-Each Loop

Question

I'm a beginner in Java and a geomatics student.

I work with an XTF image, its works like TIFF. This image store about 20000 lines called pings with several informations : coordinates, start time, stop time... The treatments I use on Intellij become too heavy but it works well. I want to cut in two the informations stored in my XTF image : 1 image with the 10000 first pings and the other with the 20000 last pings. Later I would gather the two images. My question is simple : how, with a “for each” loop can I order a limit (<=10000) ? I stored the information in a csv file.

for (XtfPing ping : xtf.getPings())
        {
            writer.write( Double.toString( ping.x) );
            writer.write( "," );
            writer.write( Double.toString( ping.y) );
            writer.write( "\n" );
        }
        writer.close();

Solution 1

If you must you an enhanced for loop, you must introduce your own counter in order to test the number of iterations :

int limit = 0;
for (XtfPing ping : xtf.getPings())
{
    if (limit <= 10000) {
        // do something
    } else {
        // do something else
    }
    limit++;
}

An alternative (if getPings() returns a Collection that supports random access (such as List) or an array) is to replace your enhanced for loop with a traditional for loop, in which the iteration number is built in.

For example, if getPings returns a List :

for (int i = 0; i < xtf.getPings().size(); i++)
{
    XtfPing ping = xtf.getPings().get(i);
    if (i <= 10000) {
        // do something
    } else {
        // do something else
    }
}

Solution 2

I know this doesn't fit exactly the OP's situation, but maybe this will help someone else looking to implement an iterate limit using Java 8:

List<Object> myList = ...
List<Object> first10000 = myList.stream().limit(10000).collect(Collectors.toList());

for (Object obj : first10000) {
    // do stuff
}

or more simply:

List<Object> myList = ...
myList.stream().limit(1000).forEach(o -> {
    // do stuff
});

Comments

[Admin]

Thank you ! It works very well and it's very simple ! :)

[Admin]

With the second solution, I have an exception : java.lang.IndexOutOfBoundsException: Index: 19101, Size: 19101

[Eran]

@Manimalis Perhaps you wrote <= instead of < in your loop.

[byInduction]

This should be the accepted answer if OP can utilize stream

[Amir Dora.]

This is proper way to do it, exactly what I was looking for.