java – How to apply the filter on groupBy in Java

How do you group first and then filter using Java?

Example: consider this Employee class: I want to group by department with a list of an employee with a salary greater than 2000.

public class Employee {
    private String department;
    private Integer salary;
    private String name;

    //getter and setter

    public Employee(String department, Integer salary, String name) {
        this.department = department;
        this.salary = salary;
        this.name = name;
    }
}

Here’s how I can do it

List list   = new ArrayList<>();
list.add(new Employee("A", 5000, "A1"));
list.add(new Employee("B", 1000, "B1"));
list.add(new Employee("C", 6000, "C1"));
list.add(new Employee("C", 7000, "C2"));

Map> collect = list.stream()
    .filter(e -> e.getSalary() > 2000)
    .collect(Collectors.groupingBy(Employee::getDepartment));

Output

{A=[Employee [department=A, salary=5000, name=A1]],
 C=[Employee [department=C, salary=6000, name=C1], Employee [department=C, salary=7000, name=C2]]}

Since there are no employees in department B with a salary above 2000. So there is no key for department B: But actually, I want to have that key with an empty list –

expected output

{A=[Employee [department=A, salary=5000, name=A1]],
 B=[],
 C=[Employee [department=C, salary=6000, name=C1], Employee [department=C, salary=7000, name=C2]]}

How can we do it?

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