Converting array to list in Java

Question

How do I convert an array to a list in Java?

I used the Arrays.asList() but the behavior (and signature) somehow changed from Java SE 1.4.2 (docs now in archive) to 8 and most snippets I found on the web use the 1.4.2 behaviour.

For example:

int[] spam = new int[] { 1, 2, 3 }; Arrays.asList(spam) 

• on 1.4.2 returns a list containing the elements 1, 2, 3
• on 1.5.0+ returns a list containing the array spam

In many cases it should be easy to detect, but sometimes it can slip unnoticed:

Assert.assertTrue(Arrays.asList(spam).indexOf(4) == -1); 

Answer 1

In your example, it is because you can't have a List of a primitive type. In other words, List<int> is not possible.

You can, however, have a List<Integer> using the Integer class that wraps the int primitive. Convert your array to a List with the Arrays.asList utility method.

Integer[] spam = new Integer[] { 1, 2, 3 }; List<Integer> list = Arrays.asList(spam); 

See this code run live at IdeOne.com.

Answer 2

In Java 8, you can use streams:

int[] spam = new int[] { 1, 2, 3 }; Arrays.stream(spam)       .boxed()       .collect(Collectors.toList());