Return a default value from a Map in Java 8

Consider the following Employee class:

public class Employee
{
    private UUID id;
    private String name;
    private int age;

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

    public void setId(UUID id)
    {
        this.id = id;
    }

    public String getName()
    {
        return name;
    }

    public void setName(String name)
    {
        this.name = name;
    }    
    
    public int getAge()
    {
        return age;
    }

    public void setAge(int age)
    {
        this.age = age;
    }
}

Let’s put some Employee objects into a hash map:

Map<Integer, Employee> employeeMap = new HashMap<>();
employeeMap.put(1, new Employee(UUID.randomUUID(), "Elvis", 50));
employeeMap.put(2, new Employee(UUID.randomUUID(), "Marylin", 18));
employeeMap.put(3, new Employee(UUID.randomUUID(), "Freddie", 25));
employeeMap.put(4, null);
employeeMap.put(5, new Employee(UUID.randomUUID(), "Mario", 43));
employeeMap.put(6, new Employee(UUID.randomUUID(), "John", 35));
employeeMap.put(7, new Employee(UUID.randomUUID(), "Julia", 55));

Note the null value for key 4. Let’s also define a default Employee object:

Employee defaultEmployee = new Employee(UUID.fromString("00000000-0000-0000-0000-000000000000"), "", -1);

Java 8 includes a new method called “getOrDefault” on the Map interface. It accepts a key, like the “get” method on the Map, but it also accepts a default object that will be returned if the key does not exist.

Can you guess what the below code will return?

Employee employee = employeeMap.getOrDefault(4, defaultEmployee);

“employee” will be null of course, as key 4 exists and its value is null. However, if you simply call the “get” method with 4 as the key input then you don’t know exactly how to interpret the null result: does 4 exist as key in the map and its value is null or does the key 4 not exist at all in the map? With getOrDefault returning 0 in this case you can be 100% sure that a null response is unambiguous.

Let’s see what the below bit of code returns:

Employee employee = employeeMap.getOrDefault(12, defaultEmployee);

This time it returns the default employee as the key 12 does not exist in the map.

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