<< Chapter < Page Chapter >> Page >
Figure 7 - Answer 6.
Q06.java:56: error: method display in class Q06 cannot be applied to given types;display(listC); ^required: ArrayList<? super Frame>found: ArrayList<JFrame>reason: actual argument ArrayList<JFrame>cannot be converted to ArrayList<? super Frame>by method invocation conversion 1 error

Back to Question 6

Answer 5

True. This program illustrates the use of a lower bounded wildcard to define a generic method thatwill accept an incoming reference to an object of a generic class where the parameter type for theobject is equal to or above the type of the wildcard in the inheritance hierarchy. The lowerbounded wildcard type for the display method is JFrame. Therefore, the display method willaccept references to ArrayList objects for parameter types JFrame, Frame, Window, Container,Component, or Object

Back to Question 5

Answer 4

False. This program illustrates the fact that a parameter of type Object is not the same as anunbounded wildcard parameter. The program refuses to compile and produces the errors shown in Figure 8 .

Figure 8 - Answer 4.
Q04.java:31: error: method display in class Q04 cannot be applied to given types;display(listA); ^required: ArrayList<Object>found: ArrayList<Button>reason: actual argument ArrayList<Button>cannot be converted to ArrayList<Object>by method invocation conversionQ04.java:40: error: method display in class Q04 cannot be applied to given types;display(listB); ^required: ArrayList<Object>found: ArrayList<Label>reason: actual argument ArrayList<Label>cannot be converted to ArrayList<Object>by method invocation conversion 2 errors

Back to Question 4

Answer 3

True. This program illustrates two scenarios where an unbounded wildcard is a useful approach:

1. When you are writing a method that can be implemented using functionality provided in theObject class. The getClass method that is called in the displaymethod is defined in the Object class.

2. When the code in a generic method doesn't depend on the type parameter.An if-else statement along with specific casts is used in the display method to isolate the calls to the getText and getLabel methods from the type parameter.

Back to Question 3

Answer 2

True. This program illustrates the use of upper bounded wildcards. The method named display will acceptand process a reference to an ArrayList object whose element types are Component or any subclassof Component. Methods that are defined in or inherited into the Component class can be calledon the elements with no requirement for a cast. Methods that are not defined in or inherited into the Component class but are defined in the element classescan be called on the elements after casting to the element type.

Back to Question 2

Answer 1

False. This program will not compile. The method named display will only accept and process a reference to an ArrayList object whose element are oftype Component. ArrayList objects whose element types are subclasses of Component do not satisfy that requirement. An attempt to compile the programproduces the errors shown in Figure 9 .

Figure 9 - Answer 1.
Q01.java:34: error: method display in class Q01 cannot be applied to given types;display(listA); ^required: ArrayList<Component>found: ArrayList<Button>reason: actual argument ArrayList<Button>cannot be converted to ArrayList<Component>by method invocation conversionQ01.java:43: error: method display in class Q01 cannot be applied to given types;display(listB); ^required: ArrayList<Component>found: ArrayList<Label>reason: actual argument ArrayList<Label>cannot be converted to ArrayList<Component>by method invocation conversion 2 errors

Back to Question 1

Miscellaneous

This section contains a variety of miscellaneous information.

Housekeeping material
  • Module name: Java4270r: Review of Wildcards
  • File: Java4270r.htm
  • Published: 10/24/13
Disclaimers:

Financial : Although the Connexions site makes it possible for you to download aPDF file for this module at no charge, and also makes it possible for you to purchase a pre-printed version of the PDF file, youshould be aware that some of the HTML elements in this module may not translate well into PDF.

I also want you to know that, I receive no financial compensation from the Connexions website even if you purchase the PDF version ofthe module.

In the past, unknown individuals have copied my modules from cnx.org, converted them to Kindle books, and placed them for sale onAmazon.com showing me as the author. I neither receive compensation for those sales nor do I know who does receive compensation. If youpurchase such a book, please be aware that it is a copy of a module that is freely available on cnx.org and that it was made andpublished without my prior knowledge.

Affiliation : I am a professor of Computer Information Technology at Austin Community College in Austin, TX.

-end-

Questions & Answers

A golfer on a fairway is 70 m away from the green, which sits below the level of the fairway by 20 m. If the golfer hits the ball at an angle of 40° with an initial speed of 20 m/s, how close to the green does she come?
Aislinn Reply
cm
tijani
what is titration
John Reply
what is physics
Siyaka Reply
A mouse of mass 200 g falls 100 m down a vertical mine shaft and lands at the bottom with a speed of 8.0 m/s. During its fall, how much work is done on the mouse by air resistance
Jude Reply
Can you compute that for me. Ty
Jude
what is the dimension formula of energy?
David Reply
what is viscosity?
David
what is inorganic
emma Reply
what is chemistry
Youesf Reply
what is inorganic
emma
Chemistry is a branch of science that deals with the study of matter,it composition,it structure and the changes it undergoes
Adjei
please, I'm a physics student and I need help in physics
Adjanou
chemistry could also be understood like the sexual attraction/repulsion of the male and female elements. the reaction varies depending on the energy differences of each given gender. + masculine -female.
Pedro
A ball is thrown straight up.it passes a 2.0m high window 7.50 m off the ground on it path up and takes 1.30 s to go past the window.what was the ball initial velocity
Krampah Reply
2. A sled plus passenger with total mass 50 kg is pulled 20 m across the snow (0.20) at constant velocity by a force directed 25° above the horizontal. Calculate (a) the work of the applied force, (b) the work of friction, and (c) the total work.
Sahid Reply
you have been hired as an espert witness in a court case involving an automobile accident. the accident involved car A of mass 1500kg which crashed into stationary car B of mass 1100kg. the driver of car A applied his brakes 15 m before he skidded and crashed into car B. after the collision, car A s
Samuel Reply
can someone explain to me, an ignorant high school student, why the trend of the graph doesn't follow the fact that the higher frequency a sound wave is, the more power it is, hence, making me think the phons output would follow this general trend?
Joseph Reply
Nevermind i just realied that the graph is the phons output for a person with normal hearing and not just the phons output of the sound waves power, I should read the entire thing next time
Joseph
Follow up question, does anyone know where I can find a graph that accuretly depicts the actual relative "power" output of sound over its frequency instead of just humans hearing
Joseph
"Generation of electrical energy from sound energy | IEEE Conference Publication | IEEE Xplore" ***ieeexplore.ieee.org/document/7150687?reload=true
Ryan
what's motion
Maurice Reply
what are the types of wave
Maurice
answer
Magreth
progressive wave
Magreth
hello friend how are you
Muhammad Reply
fine, how about you?
Mohammed
hi
Mujahid
A string is 3.00 m long with a mass of 5.00 g. The string is held taut with a tension of 500.00 N applied to the string. A pulse is sent down the string. How long does it take the pulse to travel the 3.00 m of the string?
yasuo Reply
Who can show me the full solution in this problem?
Reofrir Reply
Got questions? Join the online conversation and get instant answers!
Jobilize.com Reply

Get Jobilize Job Search Mobile App in your pocket Now!

Get it on Google Play Download on the App Store Now




Source:  OpenStax, Object-oriented programming (oop) with java. OpenStax CNX. Jun 29, 2016 Download for free at https://legacy.cnx.org/content/col11441/1.201
Google Play and the Google Play logo are trademarks of Google Inc.

Notification Switch

Would you like to follow the 'Object-oriented programming (oop) with java' conversation and receive update notifications?

Ask