Dear Konstantin,
happy new year! And a JEL question.
If I evaluate a string equality test in which one of the operands is null,
a NullPointerException results, e.g.:
x=="abc"
provokes a NullPointerException if x has the value null.
Since the equivalent test in Java simply returns false, that's not
what I was expecting. Is this intended behaviour?
The following program illustrates this:
import gnu.jel.CompiledExpression;
import gnu.jel.Evaluator;
import gnu.jel.Library;
public class Cmp {
public static void main(String[] args) throws Throwable {
Library lib = new Library(new Class[] {Cmp.ALib.class},
null, null, null, null);
compare("textValue", lib);
compare("nullValue", lib);
}
private static void compare(String func, Library lib) throws
Throwable {
String txtExpr = func;
String cmpExpr = func + "==\"abc\"";
CompiledExpression txtCompex = Evaluator.compile(txtExpr, lib);
CompiledExpression cmpCompex = Evaluator.compile(cmpExpr, lib);
System.out.println();
report(txtExpr, txtCompex);
report(cmpExpr, cmpCompex);
}
private static void report(String expr, CompiledExpression
compex) throws Throwable {
System.out.println(expr);
Object result = compex.evaluate(null);
System.out.println(" -> " + represent(result));
}
private static String represent(Object obj) {
if (obj == null) {
return "null";
}
else if (obj instanceof String) {
return "\"" + obj + "\"";
}
else {
return obj.toString();
}
}
public static class ALib {
public static String textValue() {
return "text";
}
public static String nullValue() {
return null;
}
}
}
which produces the output (JEL 2.1.2):
textValue
-> "text"
textValue=="abc"
-> false
nullValue
-> null
nullValue=="abc"
Exception in thread "main" java.lang.NullPointerException
at
java.text.RuleBasedCollator.compare(RuleBasedCollator.java:357)
at
gnu.jel.CompiledExpression.compare(CompiledExpression.java:352)
at dump.evaluate_boolean(Unknown Source)
at
gnu.jel.CompiledExpression.evaluate(CompiledExpression.java:157)
at Cmp.report(Cmp.java:25)
at Cmp.compare(Cmp.java:21)
at Cmp.main(Cmp.java:10)
Thanks!
Mark
--
Mark Taylor Astronomical Programmer Physics, Bristol University, UK
m.b.taylor@bristol.ac.uk http://www.star.bristol.ac.uk/~mbt/