Why Does Arrays.asList() Misbehave with Primitive Arrays in Java?

Why Arrays.asList() Can Be Tricky with Primitives

Java's Arrays.asList() method allows you to convert an array to a List. However, it can behave unexpectedly with primitive arrays.

Question: Why does Arrays.asList(int[]) return a List instead of List?

Answer: Java generics do not support primitive types. Instead, they use their wrapper classes (e.g., Integer, Float). Arrays.asList() returns a list of the exact same type as the array it is passed. Since int[] is an array of int, the result is List.

Question: Is there a way to convert an int[] to a List?

Answer: No, there is no direct way to convert an int[] to a List using Arrays.asList().

Question: Why doesn't autoboxing work in this case?

Answer: Autoboxing only occurs for individual primitive values, not for arrays of primitives. Therefore, int[] ints cannot be automatically converted to Integer[].

Solution:

To obtain a List from an array of primitives, you can use third-party libraries that provide additional functionality, such as Guava's com.google.common.primitive.Ints.asList() method. This method explicitly creates a List wrapper around the int[] array, where each element is boxed as an Integer.

Alternatively, if you are free to start with an Integer[] array, you can use Arrays.asList() directly as it would return a List.

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