Java 8 – streaming with objects and raw wrappers

I am using the Java 8 stream and trying to modify the object content in the foreach terminal operation

The problem I face here is that I can modify the contents of the list < employee > object, but I can't modify the contents of the list < integer >

The code snippet is as follows:

public static void streamExample() {

    List<Employee> listemp = Arrays.asList(new Employee());
    listemp.stream().forEach(a -> a.setEmptName("John Doe"));
    listemp.stream().forEach(System.out::println);
    List<Integer> listInteger = Arrays.asList(2,4,6,8,12,17,1234);
    listInteger.stream().filter(v -> v % 2 == 0).forEach(a -> a=a+1);
    listInteger.stream().forEach(System.out::println);

}

I want to know that the change is not reflected in the list because the integer object is unboxed when performing the a = a 1 operation, but I'm not sure

Solution

You don't have the best way to use stream Treat each step in the stream as modifying an existing (or creating a new) element and return it to the stream Finally, you will receive the final result, and you can use one of the final methods to finalize (and actually run) the stream:

List<Integer> listInteger = Arrays.asList(2,1234);
listInteger.stream().filter(v -> v % 2 == 0).forEach(a -> a = a + 1);
listInteger.stream().forEach(System.out::println);

Here is the initial array You want to do the following:

>Filter out some elements (this is not the last step); > Print the filtered elements (this is the last step)

To do this, you do not have to create streams. Net twice Use one:

Stream.of(2,1234)    // create stream (there're many way to do it)
      .filter(v -> v % 2 == 0)         // filter out required elements
      .map(v -> v + 1)                 // transform elements using given rule
      .forEach(System.out::println);   // finalize stream with printing out each element separately

Note: stream Of (...) create a stream, then we add two steps to the stream filter and map, and then use foreach to complete or start to create the stream