ERROR! What does this error mean?

Question

Exception in thread "main" java.util.regex.PatternSyntaxException: Illegal repetition
{adj}
at java.util.regex.Pattern.error(Pattern.java:1713)
at java.util.regex.Pattern.closure(Pattern.java:2775)
at java.util.regex.Pattern.sequence(Pattern.java:1889)
at java.util.regex.Pattern.expr(Pattern.java:1752)
at java.util.regex.Pattern.compile(Pattern.java:1460)
at java.util.regex.Pattern.<init>(Pattern.java:1133)
at java.util.regex.Pattern.compile(Pattern.java:823)
at java.lang.String.replaceFirst(String.java:2147)
at MadLibs.MasterListandStories(MadLibs.java:31)
at MadLibsMain.main(MadLibsMain.java:6)
I dont get a compile error, but if i try to replace a word in a sentence w/ something the user types in i get the above error

Answer 1

String.replaceFirst takes a regexp as first argument. {adj} is an invalid regexp because { and } mean something in a regular expression, and you usage of these in this context is wrong. You need to escape those characters to make it work, like this:
s[0].replaceFirst("\\{adj\\}", Jin.readLine("Enter an adjective: "));
s[0].replaceFirst("\\{verb\\}", Jin.readLine("Enter a verb: "));
s[0].replaceFirst("\\{verb\\}", Jin.readLine("Enter a verb: "));
s[1].replaceFirst("\\{noun\\}", Jin.readLine("Enter a noun: "));This will do what you want.