Example of a fully defined class in Java

        Here is an example of a simple class called "dog" and another class call "kennel" which uses the class "dog". Java requires that each class be in a separate file. No more than one class can be in any file. Dog and kennel are in two separate files named dog.java and kennel.java. They are saved in the same directory. When kennel.java is compiled, the compiler sees the reference to dog and looks for the dog.java file and compiles it as well. Both files must be in the same directory in order for the compiler to find them. Although this is an example of only two classes, the same principles demonstrated here can be used for any number of classes.

file dog.java

public class dog
{
//Attributes  [i.e. data]
private String name;
private String owner;
private String breed;
private int age;


//Behavior [i.e. methods]

//Constructors
public dog()  //constructor which takes no parameters, sets to default
{
name="";
owner="";
breed="";
age=0;
}

//fully parameterized constructor
public dog(String name, String owner, String breed, int age)
{
this.name=name;
this.owner=owner;
this.breed=breed;
this.age=age;
}

//copy constructor
public dog(dog someDog)
{
this.name=someDog.getName();
this.owner=someDog.getOwner();
this.breed=someDog.getBreed();
this.age=someDog.getAge();
}


//other behavior (non-constructor behavior)
public String getName()
{
return name;
}
public String getOwner()
{
return owner;
}
public String getBreed()
{
return breed;
}
public int getAge()
{
return age;
}

public int computeYearsToLive()
{
int toLive;
if(breed.equalsIgnoreCase("german"))
	{
	toLive=15-age;
	}
else if(breed.equalsIgnoreCase("boxer"))
	{
        toLive=11-age;
        }
else if(breed.equalsIgnoreCase("terrier"))
	{
        toLive=8-age;
        }
else if(breed.equalsIgnoreCase("doberman"))
	{
        toLive=13-age;
        }
else
	{
        toLive=14-age;
        }
return toLive;
}//end method computeYearsToLive()

}//end class


file  kennel.java 

import javax.swing.JOptionPane;

public class kennel
{
 public static void main( String args[] )
 {
     String tempName="",tempOwner="",  tempBreed="", output="";
     int tempAge, c, counter;
     dog dogArray[] = new dog[10];

     for( c=0 ; c <10; c++)
	 {
	     tempName=JOptionPane.showInputDialog("Enter name of dog, type quit when done.");
	     if(tempName.equalsIgnoreCase("quit"))
		 {
		     break; 
		 }
	     tempOwner=JOptionPane.showInputDialog("Enter name of owner of dog");
	     tempBreed=JOptionPane.showInputDialog("Enter breed of dog");
	     tempAge=Integer.parseInt(JOptionPane.showInputDialog("Enter age of dog"));
	     dogArray[c] = new dog(tempName, tempOwner ,tempBreed, tempAge);
	 }
     while(true)
	 {
	     tempName=JOptionPane.showInputDialog("Enter name of dog to display, type quit to exit.");
	     if(tempName.equalsIgnoreCase("quit"))
		 {
		     break;
		 }
	     for( counter =0 ; counter < c; counter++)
		 {
		     if(tempName.equalsIgnoreCase(dogArray[counter].getName()) )
			 {
			     JOptionPane.showMessageDialog(null, "Your dog info is:\n"
			     + "Name: "+dogArray[counter].getName() +
			     "\nOwner Name: "+dogArray[counter].getOwner() +
			     "\nBreed: "+dogArray[counter].getBreed()+
			     "\nAge: "+dogArray[counter].getAge()+
			     "\nYear Left to Live: "+
		      	     dogArray[counter].computeYearsToLive() );
			     break; //exit for loop
			 }//end if
		 }
	     if (counter==c)
		 {
		     JOptionPane.showMessageDialog(null, "Dog not found! He must have died.");
		 }
	 }//end while
  JOptionPane.showMessageDialog(null, "So long!");
  System.exit(0);
 }//end main()
}//end class

© Nachum Danzig December 2003