java 8 stream using filter and count

Question

I have a array list named employee.

List<Employee> employee = new ArrayList<Employee>();

I need to get the count of employees whose status is not "2" or null.

long count = 0l;
count = employee.stream()
.filter(p->!(p.getStatus().equals("2")) || p.getStatus() == null).count();

In the above query getting error like "lambda expression cannot be used in evaluation expression", Please help me to resolve this error.

The list employee contains values like

 empId  Status
  1       3
  2       4
  3       null

If the status column doesn't contains null value it is working fine.

First of all, check how you are instantiating your ArrayList. If that code is correct it should be updated to "new ArrayList<>()" (note the capital A). — isak
– isak, Commented Oct 1, 2021 at 6:48

navnath · Accepted Answer · 2021-10-01 07:16:45Z

4

It's important to check first if the status is not null then only we would be able to use the equals method on status, else we will get NullPointerException. You also don't need to declare count to 0l, count() will return you 0 when no match is found.

List<Employee> employee = new ArrayList<Employee>();
// long count = 0l;

// Status non null and not equals "2" (string)
ling count = employee.stream()
    .filter(e ->  Objects.nonNull(e.getStatus()) && (!e.getStatus().equals("2")))
    .count();

edited Oct 1, 2021 at 7:16

answered Oct 1, 2021 at 6:52

navnath

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2 Comments

Rahul Over a year ago

Is it better to use "Predicate" instead of writing Lamda expression inside the Filter?

navnath Over a year ago

Yeah, I mean Its good practice in the situation when you have a really big expression or you want to reuse same expression elsewhere

isak · Accepted Answer · 2021-10-01 06:52:37Z

1

The reason it doesn't work if an Employee has status = null is because you are trying to perform the .equals() operation on a null object. You should verify that status is not equal to null before trying to invoke the .equals() operation to avoid null pointers.

answered Oct 1, 2021 at 6:52

isak

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Comments

Jeremy Caney · Accepted Answer · 2023-11-24 06:31:26Z

1

If you want to find number of project having particular project manager using Java stream API then here you go.

public Long listOfProjectWorkingWithPM(){

       return getAllEmployees()
                .stream()
                .flatMap(pm->pm.getProjects().stream())
                .filter(project -> "Robert Downey Jr".equalsIgnoreCase(project.getProjectManager()))
                .count();

    }

edited Nov 24, 2023 at 6:31

Jeremy Caney

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answered Nov 22, 2023 at 8:47

ronak thakor

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