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True. Updates made in Java v1.7 eliminated the requirement to insert the name of a type in those angle brackets in order to make the compiler happy.
One solution is to add the generic syntax shown in the class named A10 in Listing 9 below. This will cause the program to compile and execute successfully producing an output similar to that shown in Figure 8 below.
| Listing 9 - Answer 10. |
|---|
/*File A10.java
************************************************/import java.util.*;
public class A10{ArrayList<Date>var1 = new ArrayList<Date>();
void runIt(){var1.add(new Date());
//Note the required cast in the following// statement.
System.out.println((var1.get(0)).getTime());
}//runItpublic static void main(String[]args){
new A10().runIt();}//end main}//end class A10
//=============================================// |
| Figure 8 - Answer 10. |
|---|
1378058466149 |
False: The program produces the runtime error shown in Figure 9 below. The (Date) cast is applied to the contents of the element at index 1. However, thatelement contains a reference to an object of type String.
| Figure 9 - Answer 9. |
|---|
Exception in thread "main" java.lang.ClassCastException: java.lang.String cannot
be cast to java.util.Dateat Q09.runIt(Q09.java:15)
at Q09.main(Q09.java:22) |
The program must be updated to include the cast operator (Date) shown in Listing 10 below.
| Listing 10 - Answer 8. |
|---|
/*File Q08.java
************************************************/import java.util.*;
public class Q08{ArrayList var1 = new ArrayList();void runIt(){
var1.add(new Date());//Note the required cast in the following
// statement.System.out.println(
((Date)var1.get(0)).getTime());}//runIt
public static void main(String[]args){
new Q08().runIt();}//end main}//end class Q08
//=============================================// |
False: This program produces the compiler error shown in Figure 10 below.
| Figure 10 - Answer 7. |
|---|
Q07.java:17: error: cannot find symbol
(var1.get(0)).getTime());^
symbol: method getTime()location: class Object
Note: Q07.java uses unchecked or unsafe operations.Note: Recompile with -Xlint:unchecked for details.
1 error |
B. A warning
The compiler output is shown in Figure 11 below:
| Figure 11 - Answer 6. |
|---|
Q02.java:13: warning: [unchecked] unchecked call to add(E) as a member of the rawtype ArrayList
var1.add(new Date());^
where E is a type-variable:E extends Object declared in class ArrayList
1 warning |
False. Two notes are displayed. However, the messages produced by the Java v1.7 compiler in this cases are neither error messages nor warnings. Instead they are simply notes. The notes provideinstructions on how to recompile and get more information regarding a potential problem.
False. The tentacles of generics reach into many different areas of Java in very complex ways including:
B. Compile-time type safety
False: An attempt to compile the program using the Java v1.7 compiler produces an output similar to that shown in Figure 12 below.
| Figure 12 - Answer 2. |
|---|
Note: Q02.java uses unchecked or unsafe operations.
Note: Recompile with -Xlint:unchecked for details. |
False. The Collections framework was not new in Java v1.5. It was available long before version 1.5 was released.
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 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.
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