Name: tb29552 Date: 06/08/2001


Need a more graceful message when user tries to evaluate
a method such as length() or toString() as a field:


% cat HelloWorld.java
class HelloWorld {
    static String s = "Hello World";
    public static void main(String[] args){
        System.out.println(s);
    }
}

% javac -g HelloWorld.java
% jdb HelloWorld
Initializing jdb ...
> stop in HelloWorld.main
Deferring breakpoint HelloWorld.main.
It will be set after the class is loaded.
> run
run HelloWorld
>
VM Started: Set deferred breakpoint HelloWorld.main

Breakpoint hit: "thread=main", HelloWorld.main(), line=4 bci=0
4 System.out.println(s);

main[1] print HelloWorld.s
 HelloWorld.s = "Hello World"

main[1] print HelloWorld.s.NotAField
com.sun.tools.example.debug.expr.ParseException: No instance field or method
with the name NotAField in java.lang.String
 HelloWorld.s.NotAField = null

main[1] print HelloWorld.s.length
java.lang.NullPointerException
        at com.sun.tools.jdi.MirrorImpl.validateMirrors(MirrorImpl.java:75)
        at
com.sun.tools.jdi.ObjectReferenceImpl.getValues(ObjectReferenceImpl.java:149)
        at
com.sun.tools.jdi.ObjectReferenceImpl.getValue(ObjectReferenceImpl.java:144)
        at
com.sun.tools.example.debug.expr.LValue$LValueInstanceMember.getValue(LValue.java:281)
        at
com.sun.tools.example.debug.expr.ExpressionParser.evaluate(ExpressionParser.java:54)
        at com.sun.tools.example.debug.tty.Commands.evaluate(Commands.java:114)
        at com.sun.tools.example.debug.tty.Commands.doPrint(Commands.java:1498)
        at com.sun.tools.example.debug.tty.Commands$4.action(Commands.java:1520)
        at com.sun.tools.example.debug.tty.Commands$1.run(Commands.java:67)
 HelloWorld.s.length = null


main[1] print HelloWorld.s.length()
 HelloWorld.s.length() = 11

main[1] print HelloWorld.s.toString
java.lang.NullPointerException
        at com.sun.tools.jdi.MirrorImpl.validateMirrors(MirrorImpl.java:75)
        at
com.sun.tools.jdi.ObjectReferenceImpl.getValues(ObjectReferenceImpl.java:149)
        at
com.sun.tools.jdi.ObjectReferenceImpl.getValue(ObjectReferenceImpl.java:144)
        at
com.sun.tools.example.debug.expr.LValue$LValueInstanceMember.getValue(LValue.java:281)
        at
com.sun.tools.example.debug.expr.ExpressionParser.evaluate(ExpressionParser.java:54)
        at com.sun.tools.example.debug.tty.Commands.evaluate(Commands.java:114)
        at com.sun.tools.example.debug.tty.Commands.doPrint(Commands.java:1498)
        at com.sun.tools.example.debug.tty.Commands$4.action(Commands.java:1520)
        at com.sun.tools.example.debug.tty.Commands$1.run(Commands.java:67)

main[1] print HelloWorld.s.toString()
 HelloWorld.s.toString() = "Hello World"

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