Puppy.java

public class Puppy {
        // instance variables; private
        private String _name;
        private int _age;

        // constructor
        public Puppy (String name, int age)
        {
                // constructor is called on a specific instance; let's modify that instance's variables
                _name=name;
                _age=age;
        }

        // setters and getters; used to prepare against future changes
        public void setName(String name) { _name=name;}
        public String getName() {return _name;}

        public void setAge(int age) {_age=age;}
        public int getAge() {return _age;}

        public static void main(String args[]) {

                Puppy p1=new Puppy("fido",3); // two different puppies, each with its own instance variables
                Puppy p2=new Puppy("joe",5);

                System.out.println(p1.getName()+"'s age is "+p1.getAge());
                System.out.println(p2.getName()+"'s age is "+p2.getAge());

        }
}

PuppyBadStyle.java

public class Puppy {
        // instance variables; public, which is a bad habit
        public String _name;
        public int _age;

        // constructor
        public Puppy (String name, int age)
        {
                // constructor is called on a specific instance; let's modify that instance's variables
                _name=name;
                _age=age;
        }


        public static void main(String args[]) {

                Puppy p1=new Puppy("fido",3); // two different puppies, each with its own instance variables
                Puppy p2=new Puppy("joe",5);

                System.out.println(p1._name +"'s age is "+p1._age);
                System.out.println(p2._name+"'s age is "+p2._age);

        }
}