How Can I Efficiently Convert a List to an int[] in Java Using Streams?

Converting List to int[] in Java using Streams

The conversion of a List to an int[] often requires a loop, raising the question of whether a more efficient method exists.

Java 8 introduced streams, providing a convenient solution to this problem.

With streams, the conversion process can be simplified to:

int[] example1 = list.stream().mapToInt(i -> i).toArray();
// OR
int[] example2 = list.stream().mapToInt(Integer::intValue).toArray();

Thought Process

• Streams have a toArray() method that returns an Object[], not an int[].
• Converting Integer to int in the stream requires transforming the Stream into IntStream, a stream that handles primitive types.
• The mapToInt() method takes a ToIntFunction that transforms each element from Integer to int.
• Integer#intValue can be used to directly obtain the int value, or unboxing can be utilized for automatic conversion.
• The inferred Integer type in the lambda can be omitted, resulting in:

list.stream().mapToInt(i -> i).toArray();

This streamlined process eliminates the need for loops and enhances the conversion efficiency.

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