Xxx.java:Recompile with-xlint:unchecked for details.

First, encounter problems:
When using ant to perform the build.xml of the Jasperreport Samples/charts sample, it fails to compile with the following error:
Javac
[Javac] Compiling 2 source files to E:/jiangcm/workspace-forict-myeclipse/jasperreports/demo/samples/charts
[Javac] Note: E:/jiangcm/workspace-forict-myeclipse/jasperreports/demo/samples/charts/chartsapp.javaa non-checked or unsafe operation was used.
[Javac] Note: To learn more, recompile with-xlint:unchecked.

Second, check the information, know that the cause of the generic, the online search solution mainly has the following:
1. Compile-time with the parameter-source 1.4
1. Role@SupressWarnings ("unchecked")Comments
3. Update your code, using List<object>. An instance of list<object> can accept any type of object, as if it were a prototype list. However, the compiler does not error.
(Above three methods Source: http://www.matrix.org.cn/resource/article/43/43634_java_generics.html)

4. If you use theAnt, using Build.xmlCompile the words, you can right-click the Build.xml file,
-----Make and execute, select parameters,Enter-xlint:unchecked in "program parameters"To

5. Find a similar statement inside Build.xml, plus a sentence:
<!--Java Compile--
<target name= "Compile" depends= "init" >
<javac srcdir= "src" destdir= "${classdir}"
Deprecation= "on" encoding= "windows-31j" debug= "on" includes= "**/jp/**" >
<compilerarg value= "-xlint:unchecked"/> ' <!--is this sentence!! -
<classpath refid= "Project.class.path"/>
</javac>
</target>
(Source of both methods: http://www.itwenku.com/java/12/47796.htm)

Iii. Self-Test and conclusion

The first type:
"Compile-time with parameter-source 1.4" method of Use:
Find a similar statement inside Build.xml, plus a sentence:
<javac srcdir= "${src.dir}" destdir= "${classes.dir}" >
<classpath refid= "Classpath"/>
<compilerarg line= "-source 1.5"/> ' <!--that's the word! Note that unlike the fifth way, the line label is not value! -
</javac>
Compile the pass, the report under charts appears!

The second type:
"Use @supresswarnings (" unchecked ") Comment:
This comment is added to the main function of Chartsapp.java, but it does not work, and the hint error remains "[Javac] Note: To learn more, use-xlint:unchecked to recompile. "And what's going on?"

Found the answer in an article:
Http://www.matrix.org.cn/resource/article/43/43864_Generic_Types.html
At the time of writing this article, Javac does not support @suppresswarnings annotations. Expect to be supported in Java 5.1.

The third type:

1. Before JDK5.0. We can write vector v in this way without a problem. But after 5.0, a generic will be written as a vector <T> such as a String that is put in a vector <String> it will know the type there is no such warning.
Such as:

Public Vector <StockData> Myvector; Over here
Myvector = new Vector <StockData> (); And here it is.

2. Change the code to use generic mode:
The original code:
Map parameters = new HashMap ();
Parameters.put ("Maxorderid", New Integer (12500));
The changed code:
map<string,integer> parameters = new hashmap<string,integer> ();
Parameters.put ("Maxorderid", New Integer (12500));
Or:
map<object,object> parameters = new hashmap<object,object> ();
Parameters.put ("Maxorderid", New Integer (12500));

After the change, smoothly through the compilation, also can see the report!!

Java uses unchecked or unsafe operations
Import java.util.*;
Class Testvector
{

{
  int b=0;
  Vector v=new vector ();
  System.out.println ("Please enter Number:");
  while (true)
  {
   Try
   {
    B=system.in.read ();
   }
   catch (Exception e)
   {
    E.printstacktrace ();
   }
   if (b== ' \ r ' | | b== ' \ n ')
    Break
   Else
   {
    int num =b-' 0 ';
    
   }
  
  int sum=0;
  Enumeration e=v.elements ();
  while (E.hasmoreelements ())
  {
   Integer intobj= (integer) e.nextelement ();
   Sum+=intobj.intvalue ();
  }
  SYSTEM.OUT.PRINTLN (sum);
}
}

I can run here and estimate the problem of generics: You will

Enumeration e=v.elements (); instead: Enumeration<integer> e=v.elements ();

The fourth type:

Verified invalid;

The fifth type:
<javac srcdir= "src" destdir= "${classdir}"
deprecation= "on" encoding= "windows-31j" debug= "on" includes= "**/jp/**" >
<compilerarg value= "-xlint:unchecked"/> ' <!--is this sentence!! -
<classpath refid= "Project.class.path"/>
</javac>

Add "<compilerarg value="-xlint:unchecked "/>", after the "warning", but the compilation passed, you can see the report!
The compile prompt is as follows:
[Javac] Compiling 2 source files to E:/jiangcm/workspace-forict-myeclipse/jasperreports/demo/samples/charts
[Javac] e:/jiangcm/workspace-forict-myeclipse/jasperreports/demo/samples/charts/chartsapp.java:115: Warning: [Unchecked] A call to a put (k,v) that is a member of the normal type java.util.Map is unchecked
[Javac] Parameters.put ("Maxorderid", New Integer (12500));
[Javac] ^
[Javac] 1 warning


Hehe, the answer is colorful, all roads through Rome, this time not only solves the problem, but also found four ways to solve the problem.


Resources:
Generics in 1.J2SE 5.0
Budi Kurniawan
Http://www.matrix.org.cn/resource/article/43/43634_java_generics.html
2.Eclipse in the JSP in the error "to learn more information, please use-xlint:unchecked recompile", specifically on the menu how to do?
Http://www.itwenku.com/java/12/47796.htm
3. Generic type, first part
Author: David Flanagan
Http://www.matrix.org.cn/resource/article/43/43864_Generic_Types.html
4. FAQ about Ant
Http://www.blogjava.net/luckyrobbie/articles/24117.html

Q. How do I pass-xlint or-xlint:unchecked to 1.5 javac task?
A:pass it as Compilerarg nested <compilerarg> to specify.

<compilerarg value= "-xlint"/>
<!--or--
<compilerarg value= "-xlint:unchecked"/>

Xxx.java:Recompile with-xlint:unchecked for details.