CODEWITHSUNDEEP
groovystring-comparison
ViciOs
ViciOs

Reputation: 164

Groovy: comparing `"8" > 16` works and `"16" > 16` throws ClassCastException exception

I execute following expression in Groovy shell:

groovy:000> '8' > 16

===> true

But when execute expression like:

groovy:000> '16' > 16

it throws following exception:

ERROR java.lang.ClassCastException:

java.lang.Integer cannot be cast to java.lang.String

In case of '8' > 16, I think it is '8' > '16', so it compares dictionary order of two strings. Why it cannot convert 16 to '16'? What does this exception mean?

My groovy version is:

Groovy Version: 2.4.8 JVM: 1.7.0_80 Vendor: Oracle Corporation OS: Linux

Upvotes: 2

Views: 680

Answers (1)

Szymon Stepniak
Szymon Stepniak

Reputation: 42224

Groovy adds via DefaultGroovyMethods a custom compareTo() methods to Character and Number classes that allows you to compare character's ASCII ordinal number against a number value. It means that when you execute:

'z' > 12

in a Groovy Shell, compiler calls:

org.codehaus.groovy.runtime.DefaultGroovyMethods.compareTo((char) 'z', 12)

method instead, because a single character String is equivalent of Character. And similar thing happens when you execute:

12 > 'z'

Compiler sees it as:

org.codehaus.groovy.runtime.DefaultGroovyMethods.compareTo(12, (char) 'z')

However, when you execute expression like:

'16' > 16

following method gets executed:

'16'.compareTo(16) // String.compareTo(String other) <-- passing Integer value throws ClassCastException

It happens because String of size 2 (or more) is not an equivalent of a Character. This is why you get:

ERROR java.lang.ClassCastException:
java.lang.Integer cannot be cast to java.lang.String

because there is no method String.compareTo(Number n) and compiler does not cast Number directly to String in this case. It tries to execute String.compareTo(String other) method and passing a parameter with a different type than a String throws ClassCastException in this case.

If you cast 16 to String directly, compiler wont complain anymore:

'16' > (String) 16

Hope it helps.

Upvotes: 4

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