How can I convert List to int

Roll up your sleeves: The detailed approach

Well, staying ahead of the curve means exploring all available options. Trust me, Java 8's feature toolbox is filled with them!

Let's also use some well-known libraries like Guava and Apache Commons Lang.

// Guava's in the house!
int[] array = Ints.toArray(list);

// Apache Commons Lang showing who's boss!
int[] array = ArrayUtils.toPrimitive(list.toArray(new Integer[0]));
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While Guava goes down memory lane with no intermediate arrays, Apache Commons Lang simplifies transitions and avoids manual iteration.

Manual conversion: DIY style

In case you're a do-it-yourself type, here's how to manually convert List<Integer> to int[]:

int[] array = new int[list.size()];

for (int i = 0; i < list.size(); i++) {
    array[i] = list.get(i); // Auto-unboxing like a boss!
}
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This isn't as fancy as streams, but it gets the job done. Practical and reliable, it's like the good ol' family car. Not a Ferrari, but it takes you where you need to be.

When nulls throw a party

Say your List<Integer> contains some party poopers - null values. You can run into a NullPointerException. Here's how you can show them the door:

// Kicking out the null party crashers
int[] array = list.stream()
                  .filter(Objects::nonNull)
                  .mapToInt(Integer::intValue)
                  .toArray();
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Even during manual iteration, don't let null values crash the conversion party:

// When nulls try to crash the party
for (int i = 0; i < list.size(); i++) {
    Integer value = list.get(i);
    array[i] = (value != null ? value : defaultValue); // Choose your substitute for wallflowers
}
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Times when streams aren't life saviors

Streams are wonderful, but they might not always be the fastest or memory-friendliest. Especially for small list sizes, a manual loop might just do the trick better!

Also, consider your environment. In a concurrent or multi-threaded scenario, streams offer tantalizing parallel processing using parallelStream().