CS121/IS232 Laboratory 3
Using a constructor
When you get an instance of a class, a method called a constructor is always executed first. The
classes that we have written so far have default constructors. That means that Java provides one
for the class that really doesn’t do anything.
However, most classes have constructors written by the programmer. These may provide data for
variables or run certain methods. For example, we could assign values to the name and age of the
panda using a constructor, as follows:
public Panda ()
{
name = "Mei Ling";
age = 6;
} // constructor
Then when the ZooKeeper class gets a new panda, values for the name and age will be given
right away. No change has to be made to the ZooKeeper class to do this. The line
Panda panda = new Panda ();
previously ran the default constructor. Now it will run the one written by the programmer
instead.
This again hard codes the data into the program. But the constructor can be used more generally
as well. We can have the constructor run the getData () method. Since the method is right in the
class, we do not have to say which class to use.
/*
* Created on Jan 29, 2007
* Created by Carol Wolf
* Course: CS 121/IS 223
*/
package zoo;
/**
* A class that describes a panda.
* Pandas are native to China and eat bamboo shoots.
*/
public class Panda
{
private String name;
private int age;
public Panda ()
{
name = "Mei Ling";
age = 6;
} // constructor
public void displayData ()
{
System.out.println (name + "'s age is " + age);
