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.

View all posts related to Java here.

Advertisements

About Andras Nemes
I'm a .NET/Java developer living and working in Stockholm, Sweden.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s

ultimatemindsettoday

A great WordPress.com site

Elliot Balynn's Blog

A directory of wonderful thoughts

Robin Sedlaczek's Blog

Developer on Microsoft Technologies

HarsH ReaLiTy

My goal with this blog is to offend everyone in the world at least once with my words… so no one has a reason to have a heightened sense of themselves. We are all ignorant, we are all found wanting, we are all bad people sometimes.

Softwarearchitektur in der Praxis

Wissenswertes zu Webentwicklung, Domain-Driven Design und Microservices

the software architecture

thoughts, ideas, diagrams,enterprise code, design pattern , solution designs

Technology Talks

on Microsoft technologies, Web, Android and others

Software Engineering

Web development

Disparate Opinions

Various tidbits

chsakell's Blog

Anything around ASP.NET MVC,WEB API, WCF, Entity Framework & AngularJS

Cyber Matters

Bite-size insight on Cyber Security for the not too technical.

Guru N Guns's

OneSolution To dOTnET.

Johnny Zraiby

Measuring programming progress by lines of code is like measuring aircraft building progress by weight.

%d bloggers like this: