How to get rid of NullPointerException in a method using Streams API and Optional?

Question

Given the following task. We have an Employee and a Company classes. Each instance of Employee class is stored in array Employee[] employees in the Company class. I need a method which finds an instance of Employee in the array Employee[] employees by id.

I managed to write the following code:

public class Employee {
    protected final int id;
    protected String name;

    public Employee(int id, String name) {
        this.id = id;
        this.name= name;
    }
    public int getId() {
        return id;
    }
}

public class Company {
    private Employee[] employees;
    private int size;
    private static final int defaultCapacity = 5;
    
    public Company() {
        this(defaultCapacity);
    }
    
    public Company(int capacity) {
        if (capacity <= 0)
             throw new RuntimeException("capacity is required");
        employees = new Employee[capacity];
    }

    public Employee findEmployee(int id) {
        for (int i = 0; i < size; i++) {
            if(employees[i].getId() == id) {
                return employees[i];
            }
        }
        return null;
    }
}

The problem is that my method public Employee findEmployee(int id) throws NullPointerException if an element of the Employee[] employees equals null.

How can I rewrite the method public Employee findEmployee(int id) using Streams API and Optional in order to get rid of NullPointerException in the method public Employee findEmployee(int id)?

Youcef LAIDANI · Accepted Answer · 2022-11-22T13:22:24.410

Something like this:

public Optional<Employee> findEmployee(int id) {
    return Stream.of(employees)
            .filter(Objects::nonNull) // <---------------
            .filter(employee -> employee.getId() == id)
            .findFirst();
}

This will return an empty Optional if no result is found. The first filter will filter all non-null employees, then the second filter will check the id.

If you want to get Employee instead of Optional, then you can use:

public Employee findEmployee(int id) {
    return Stream.of(employees)
            .filter(Objects::nonNull)
            .filter(employee -> employee.getId() == id)
            .findFirst()
            .orElse(null);
}

Or if you want to go deeper, you even throw an exception if no employee is found, for example:

public Employee findEmployee(int id) {
    return Stream.of(employees)
            .filter(Objects::nonNull)
            .filter(employee -> employee.getId() == id)
            .findFirst()
            .orElseThrow(() -> new RuntimeException("No employee found."));
}

How to get rid of NullPointerException in a method using Streams API and Optional?

1 Answers1