sum of arraylist java 8

To find the sum of all the elements of an ArrayList in Java 8, you can use the stream API and the sum method.

Here's an example of how to find the sum of all the elements of an ArrayList of Integer objects using the stream API:

ArrayList<Integer> list = new ArrayList<>(Arrays.asList(1, 2, 3, 4, 5));
int sum = list.stream().mapToInt(i -> i).sum();
System.out.println(sum);  // prints 15

In this example, we're using the stream method to create a stream of Integer objects, the mapToInt method to convert the stream to an IntStream, and the sum method to sum the elements of the stream.

You can also use the reduce method of the IntStream class to find the sum of all the elements of an ArrayList. Here's an example of how to do this:

ArrayList<Integer> list = new ArrayList<>(Arrays.asList(1, 2, 3, 4, 5));
int sum = list.stream().mapToInt(i -> i).reduce(0, (a, b) -> a + b);
System.out.println(sum);  // prints 15

In this example, we're using the reduce method to apply a binary operator to the elements of the stream, starting with an initial value of 0. The binary operator adds the two operands together, resulting in the sum of all the elements of the stream.

You can find more information about the stream API and examples of how to use it in the Java documentation.