eval : Java Glossary

go to home page E words local find full screen, hide local find menu Google search web for more information on this topic jump to foot of page translate this page with Babelfish punctuation 0-9 A B C D E F G H I J K L M N O P Q R S T U V W X Y Z (all) ©1996-2009 Roedy Green, Canadian Mind Products
eval
In many languages you can take a dynamically created String such as "6*(4+6^2)-cos(20)" and ask to have it evaluated, as if it were a miniature computer program. The function to do this often has a name such as eval. Java has no such function. What can you do? Here are six different approaches:
  1. Compose a miniature Java program on the fly, one complete *.java file and invoke sun.tools.javac.Main instead of execing javac.exe. Use Class.forName or reflection on to then execute the dynamically compiled method.
  2. Similar to the method above, but directly generate some byte codes for a miniature class.
    JASM on how
  3. Write a parser using one of the compiler-compiler tools such as JavaCC.
  4. Use a different language that supports dynamic scripting that is compatible with Java, e.g. BeanShell, Jpython or FESI.
  5. Use Java 1.6 which has scripting.
  6. For simple applications, all you need is a Hashtable that has lookup by String to give you a delegate object to execute some prewritten piece of code.

Learning More

Sun’s JDK Technote Guide on Scripting : available:
Sun’s Javadoc on javax.script package : available:

CMP homejump to top You can get the freshest copy of this page from: or possibly from your local J: drive (Java virtual drive/mindprod.com website mirror)
http://mindprod.com/jgloss/eval.html J:\mindprod\jgloss\eval.html
CMP logofeedback Please email your feedback for publication, errors, omissions, typos, formatting errors, ambiguities, unclear wording, broken/redirected link reports, suggestions to improve this page or comments to Roedy Green : feedback email
mindprod.com IP:[65.110.21.43]
view BlogYour face IP:[38.107.191.105]
You are visitor number 32,410.