30_Person.java

public class Person {

    private String firstName;
    private String lastName;
    private int age;

    public String getFirstName(){

        return firstName;
    }

    public String getLastName(){

        return lastName;
    }

    public int getAge(){

        return age;
    }

    public void setFirstName(String firstName){

        this.firstName = firstName;
    }

    public void setLastName(String lastName){

        this.lastName = lastName;
    }

    public void setAge(int age){

        if(age < 0 || age > 100)
            this.age = 0;
        else
            this.age = age;
    }

    public boolean isTeen(){

        if(age > 12 && age < 20)
            return true;

        return false;
    }

    public String getFullName(){

        if(firstName.isEmpty() && lastName.isEmpty())
            return "";

        if(firstName.isEmpty())
            return lastName;

        if(lastName.isEmpty())
            return firstName;

        return firstName + " " + lastName;
    }
}