Defining Classes I - Java - page 238

• Encapsulation means that the data and the actions are combined into a single item

(in our case, a class object) and that the details of the implementation are hidden.
Making all instance variables private is part of the encapsulation process.

• A class can have two (or more) different definitions for the same method name,

provided the two definitions have different numbers of parameters or some
parameters of differing types. This is called overloading the method name.

• A constructor is a variety of method that is called when you create an object of the

class using new . A constructor is intended to be used to perform initialization tasks
such as initializing instance variables. A constructor must have the same name as
the class to which it belongs.

• A constructor with no parameters is called a no-argument constructor . If your class

definition includes no constructor definitions at all, then Java automatically pro-
vides a no-argument constructor. If your class definition contains any constructor
definitions at all, then no additional constructors are provided by Java. Your class
definitions should usually include a no-argument constructor.

Answers to Self-Test Exercises
1. public void makeItNewYears()
{
month = "January";
day = 1;
}

2. public void yellIfNewYear()
{
if ( (month.equalsIgnorewCase("January")) && (day == 1) )
System.out.println("Hurrah!");
else
System.out.println("Not New Year's Day.");
}

3. public int getNextYear()
{
int nextYear = year + 1;
return nextYear;
}

4. public void happyGreeting()
{
int count;
for (count = 1; count <= day; count++)
System.out.println("Happy Days!");
}