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() {
        if(age<0||age>100){return 0;}
        return age;
    }
    public void setFirstName(String firstName) {
        this.firstName=firstName;
    }
    public void setLastName(String lastName) {
        this.lastName=lastName;
    }
    public void setAge(int age) {
        this.age=age;
    }
    public boolean isTeen() {
        return age > 12 && age < 20;
    }
    public String getFullName() {
        if(firstName==""){return lastName+"";}
        if(lastName==""){return firstName+"";}
        return (firstName+" "+lastName);
    }
}