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False. This is an unsuccessful call to a generic method where the type of the object passed to the method isabove the upper bound on the specified generic type for the method. An attempt to compile the program results in the errorshown in Figure 11 below.
| Figure 11 - Answer 8. |
|---|
Q08.java:25: error: method runIt in class Foo
cannot be applied to given types;aFoo.runIt(aFrame);
^required: T
found: Framereason: inferred type does not conform to declared bound(s)
inferred: Framebound(s): JFrame
where T is a type-variable:T extends JFrame declared in method<T>runIt(T)
1 error |
True. This is a successful call to a generic method where the generic type for the method is above (in the inheritance hierarchy) the type of object passed as a parameter.
One possible solution is shown in Listing 8 below.
| Listing 8 - Answer 6. |
|---|
/*File A06Foo.java
************************************************/import java.awt.*;
public class A06Foo<T extends Component>{
private T param;public A06Foo(T param){this.param = param;
}//end constructorpublic void runIt(){System.out.println("Object instantiated.");
System.out.println(param.getClass());}//end runIt
}//end A06Foo//=============================================// |
One possible solution is shown in Listing 9 below where T extends Component . However, causing T to extend Window, Container, Component, or Object would all be valid solutions. The upper bound for T must be at or above thetype being passed as a type parameter in the inheritance hierarchy.
| Listing 9 - Answer 5. |
|---|
/*File A05Foo.java
************************************************/import java.awt.*;
public class A05Foo<T extends Component>{
public void runIt(){System.out.println("Object instantiated.");
}//end runIt}//end A05Foo
//=============================================// |
False. This program produces the compiler error shown in Figure 12 below. The problem is that the upper bound for the type parameter in the class named Foo(Frame) is below the type passed as a parameter (Window) in the attempt to instantiate an object of the class named Foo.
| Figure 12 - Answer 4. |
|---|
Q04.java:20: error: type argument Window is not within bounds
of type-variable TFoo<Window>aFoo = new Foo<>();
^where T is a type-variable:
T extends Frame declared in class FooQ04.java:20: error: cannot infer type arguments for Foo<>;
Foo<Window>aFoo = new Foo<>();
^reason: no instance(s) of type variable(s) T exist so that
Foo<T>conforms to
Foo<Window>where T is a type-variable:
T extends Frame declared in class Foo2 errors |
True. A type variable with multiple bounds is a subtype of all the types listed in the bound. If one of the bounds is a class, it must be specified first.
False. The correct statement is:
"To declare a bounded type parameter, list the type parameter's name, followed by the extends keyword, followed by its upper bound. Note that, in this context, extends is used in a general sense to mean either "extends" (as in classes) or "implements" (as in interfaces)."
True. There may be times when you want to restrict the types that can be used as type arguments in a parameterized type. For example, a method that operates on numbers might only want to accept instances of Number or its subclasses. This is what bounded type parameters are for.
This section contains a variety of miscellaneous information.
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 compensationfor those sales nor do I know who does receive compensation. If you purchase such a book, please be aware that it is a copy of a modulethat is freely available on cnx.org and that it was made and published without my prior knowledge.
Affiliation : I am a professor of Computer Information Technology at Austin Community College in Austin, TX.
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