Java JSP Application Hosting Web Hosting, website hosting, web site hosting , web page hosting Apache, PHP, MySQL, PERL, servlets Java, JSP  Java JSP Application Hosting Web Hosting website hosting, web site hosting, web page hosting Apache, PHP, MySQL, PERL, servlets Java, JSP,Python Java JSP Application Hosting Web Hosting website hosting, web site hosting, web page hosting Apache, PHP, MySQL, PERL, servlets Java, JSP,Python Java JSP Application Hosting Web Hosting website hosting, web site hosting, web page hosting Apache, PHP, MySQL, PERL, servlets Java, JSP,Python Java JSP Application Hosting Web Hosting website hosting, web site hosting, web page hosting, Apache, PHP, MySQL, PERL, servlets Java, JSP,Python
Java JSP Application Hosting Web Hosting, website hosting, web site hosting, web page hosting, Apache, PHP, MySQL, PERL, servlets Java, JSP, Python Java JSP Application Hosting Web Hosting, website hosting, web site hosting, web page hosting, Apache, PHP, MySQL, PERL, servlets Java, Python,JSP
Java JSP Application Hosting Web Hosting Sign-Up Java JSP Application Hosting Fund Raising, Fundraising, web hosting, website hosting, web site hosting  Java JSP Application Hosting Resellers web hosting, website hosting, web site hosting Java JSP Application Hosting EZ Site Control Panel for web hosting,website hosting, web site hosting
Java JSP Application Hosting Web Hosting, website hosting, web site hosting , web page hosting Apache, PHP, MySQL, PERL, servlets Java, Python,JSP,  Fundraising
Java JSP Application Hosting Fund Raising, Fundraising, web hosting, website hosting, web site hosting
WWW.

Call Us Toll-Free
(877) 256-0328

Outside USA
1 - (201) 505-0430

Java JSP Application Hosting Welcome Java JSP Application Hosting Web Hosting Plans Overview , Fund Raising, Fundraising, web hosting, website hosting, web site hosting Java JSP Application Hosting Fund Raising, Fundraising, web hosting Java JSP Application Hosting Resellers, web Hosting Java JSP Application Hosting Web Design, web Hosting Java JSP Application Hosting Extra Services,  web Hosting Java JSP Application Hosting Traffic Booster, web hosting Java JSP Application Hosting Traffic Booster, web hosting Java JSP Application Hosting Technical Support,  web Hosting Java JSP Application Hosting webmaster tips,  web Hosting Java JSP Application Hosting 30 Day Money Back, web hosting Java JSP Application Hosting Legal Notices for Web Hosting Java JSP Application Hosting Glossary Computer Terms for web Hosting Java JSP Application Hosting Contact Information - web hosting

Site Map
Java JSP Application Hosting Web Hosting, website hosting, web site hosting , web page hosting Apache, PHP, MySQL, PERL, servlets Java, Python, JSP Java JSP Application Hosting Java JSP Application Hosting Java JSP Application Hosting Java JSP Application Hosting Java JSP Application Hosting Answers to Questions and Exercises: Objects (The Java™ Tutorials > Learning the Java Language > Classes and Objects)
Trail: Learning the Java Language
Lesson: Classes and Objects
Home Page > Learning the Java Language > Classes and Objects
Answers to Questions and Exercises: Objects

Questions

Question 1: What's wrong with the following program?
public class SomethingIsWrong {
    public static void main(String[] args) {
        Rectangle myRect;
        myRect.width = 40;
        myRect.height = 50;
        System.out.println("myRect's area is " + myRect.area());
    }
}
Answer 1: The code never creates a Rectangle object. With this simple program, the compiler generates an error. However, in a more realistic situation, myRect might be initialized to null in one place, say in a constructor, and used later. In that case, the program will compile just fine, but will generate a NullPointerException at runtime.

Question 2: The following code creates one Point object and one Rectangle object. How many references to those objects exist after the code executes? Is either object eligible for garbage collection?

...
Point point = new Point(2,4);
Rectangle rectangle = new Rectangle(point, 20, 20);
point = null;
...
Answer 2: There is one reference to the Point object and one to the Rectangle object. Neither object is eligible for garbage collection.

Question: How does a program destroy an object that it creates?
Answer: A program does not explicitly destroy objects. A program can set all references to an object to null so that it becomes eligible for garbage collection. But the program does not actually destroy objects.


Exercises

Exercise 1: Fix the program called SomethingIsWrong shown in Question 1.
Answer 1: See SomethingIsRight

public class SomethingIsRight {
    public static void main(String[] args) {
        Rectangle myRect = new Rectangle();
        myRect.width = 40;
        myRect.height = 50;
        System.out.println("myRect's area is " + myRect.area());
    }
}

Exercise 2: Given the following class, called NumberHolder, write some code that creates an instance of the class, initializes its two member variables, and then displays the value of each member variable.

public class NumberHolder {
    public int anInt;
    public float aFloat;
}

Answer 2: See NumberHolderDisplay
public class NumberHolderDisplay {
    public static void main(String[] args) {
	NumberHolder aNumberHolder = new NumberHolder();
	aNumberHolder.anInt = 1;
	aNumberHolder.aFloat = 2.3f;
	System.out.println(aNumberHolder.anInt);
	System.out.println(aNumberHolder.aFloat);
    }
}
Previous page: Questions and Exercises: Objects
 
 
 

Add to My Yahoo!

XML icon

Add to Google

 

 

 

 

 

 

 

 

 

 

 

JSP Servlets Tomcat mysql Java JSP Servlets Tomcat mysql Java JSP Servlets Tomcat mysql Java JSP Servlets Tomcat mysql Java JSP at JSP.aldenWEBhosting.com Servlets at servlets.aldenWEBhosting.com Tomcat at Tomcat.aldenWEBhosting.com mysql at mysql.aldenWEBhosting.com Java at Java.aldenWEBhosting.com Web Hosts Portal Web Links Web Links Web Hosting JSP Solutions Web Links JSP Solutions Web Hosting Servlets Solutions Web Links Servlets Solutions Web Hosting Web Links Web Links . . .
.
.
. .
.
. .
. . . . . . . . . . . jsp hosting servlets hosting web hosting web sites designed cheap web hosting web site hosting myspace web hosting