CS2514

Introduction to Java

Dr Derek Bridge

School of Computer Science & Information Technology

University College Cork

Class definitions

• So far, we've been creating objects using class definitions from the Java SE class library
  • More than 3500 classes
• But we often have to define our own classes
• In these lectures, we will typically put code into two files
  • One will contain the class definition
  • The other will contain the main method – for testing the class definition

class DogTester {

    public static void main(String[] args) {
        Dog d1 = new Dog();
        Dog d2 = new Dog();
        
        d1.bark();
        d2.bark();
        
        d1.setName("Charles");
        d2.setName("Colin");
        
        d1.setAge(2);
        d2.setAge(7);
        
        d1.setBreed("Charlywawa");
        d2.setBreed("Colombian Drug Lord");
        
        int age_of_d1 = d1.getAge();
        System.out.println(age_of_d1);
        
        System.out.println(d1.getAge());
        
        System.out.println(d2.getName() + " is a " + d2.getAge() + " year old " + d2.getBreed());
        
        System.out.println(d1.toString());
        
        System.out.println(d1);
    }
}

The interface of Dog

• public void bark()
• public void setName(String s)
• public void setAge(int n)
• public void setBreed(String s)
• public String getName()
• public int getAge()
• public String getBreed()
• public String toString()

Method signatures

• The signature of a method, e.g.:
  • public void setBreed(String s)
  • public String getName()
  tells us
  • method name
  • how many parameters, in what order and what type of data each must be
  • the type of the result that it returns, if anything

Getters and setters

• Informally, we refer to some instance methods as getters and others as setters
  • Q: Which of Dog's instance methods are getters?
  • Q: Which are setters?
  • Q: Which one is neither?
  • Q: What can we say about the signatures of getters versus the signatures of setters?