Calling method after Optional.filter() without passing in object

问题

I can understand the below:

user
  .filter(u -> "Sam".equals(u.getName()))
  .ifPresent(this::doSomethingWithUser);

if user.getName is equal to "Sam" then pass user to local method doSomethingWithUser().

However, what if I simply wanted to call a local method, without passing user but keeping the check that user.getName is equal to "Sam"?

Does this use case make using Optional redundant?

回答1:

Just ignore the mandatory function parameter. This means you cannot use shorthand :: syntax and goes like this:

user
  .filter(u -> "Sam".equals(u.getName()))
  .ifPresent(u -> doSomethingWithoutUser());

回答2:

You can just check for the presence of the Optional for such case:

if(user.filter(u -> "Sam".equals(u.getName()).isPresent()) {
    // call your method without user
}

来源：https://stackoverflow.com/questions/58729976/calling-method-after-optional-filter-without-passing-in-object