Hashtable in JDK 1.5.0
Hashtable in JDK 1.5.0
In order to run Java programs on the new JDK version 1.5 'Tiger'
virtual machine written for JDK 1.4.2 or any other previous JDK
package, compile the program with -Xlint:unchecked
option.
javac -Xlint:deprecation -Xlint:unchecked *.java
The compiled program will run on the new 1.5 vertual machine as is.
If the program uses Hashtable, though, the compiler will give off some
warning like this.
warning: [unchecked] unchecked call to put(K,V)
as a member of the raw type java.util.Hashtable
In this case, specify the types for the key and value. In the
following case, the key and value are typed as JMenuItem and Integer
objects, respectively.
private Hashtable<JMenuItem, Integer> comp=
new Hashtable<JMenuItem, Integer>();
By specifying the types for the Hashtable class, the program can check
the types for the key and value at run time. This means, there is no
need to cast the generic Object class object every time you call get(key,
value) function.
Integer n=(Integer)comp.get(source);
-->
Integer n=comp.get(source);
It is even possible to 'nest' the type specification. If the elements
of a hashtable have the type hashtable, specify the element type with
inequal signs as usual.
Hashtable<String, Hashtable<Integer, String>> hash
=new Hashtable<String, Hashtable<Integer, String>>();
Finally, compile the program without the -Xlint:unchecked option and the warnings should dissapear.
javac -Xlint:deprecation *.java
Now, the program is safely converted for the new virtual machine. Happy programming!
Erica Asai
Last Modifed: Sun Jun 15 22:28:34 2003
