Insert a non-existent value into 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));

Suppose that we run the below bit of code later on in the programme:

employeeMap.put(2, new Employee(UUID.randomUUID(), "Anna", 20));

You’ll probably know that this will replace the original record at key 2 – Marylin – with the new one – Anna.

This can be prevented in Java 8 with the new putIfAbsent method:

employeeMap.putIfAbsent(2, new Employee(UUID.randomUUID(), "Anna", 20));

This bit of code won’t have any effect on the employee map as key 2 already exists.

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