There is a collection of 20 objects of a POJO class. I Want to write a method that return objects with distinct value. Now this is my Pogo class

```
class Student {

    private String firstName;

    private String lastName;

    public String getFirstName() {
        return firstName;
    }

    public void setFirstName( String firstName ) {
        this.firstName = firstName;
    }

    public String getLastName() {
        return lastName;
    }

    public void setLastName( String lastName ) {
        this.lastName = lastName;
    }
}

```

Now i want some method which returns unique last names values. I could not understand which logic i have to put in this.