java - Regular expression matching fully qualified class names

Question

What is the best way to match fully qualified Java class name in a text?

Examples: java.lang.Reflect, java.util.ArrayList, org.hibernate.Hibernate.

question from:https://stackoverflow.com/questions/5205339/regular-expression-matching-fully-qualified-class-names

Answer 1

A Java fully qualified class name (lets say "N") has the structure

N.N.N.N

The "N" part must be a Java identifier. Java identifiers cannot start with a number, but after the initial character they may use any combination of letters and digits, underscores or dollar signs:

([a-zA-Z_$][a-zA-Zd_$]*.)*[a-zA-Z_$][a-zA-Zd_$]*
------------------------    -----------------------
          N                           N

They can also not be a reserved word (like import, true or null). If you want to check plausibility only, the above is enough. If you also want to check validity, you must check against a list of reserved words as well.

Java identifiers may contain any Unicode letter instead of "latin only". If you want to check for this as well, use Unicode character classes:

([p{Letter}_$][p{Letter}p{Number}_$]*.)*[p{Letter}_$][p{Letter}p{Number}_$]*

or, for short

([p{L}_$][p{L}p{N}_$]*.)*[p{L}_$][p{L}p{N}_$]*

The Java Language Specification, (section 3.8) has all details about valid identifier names.

Also see the answer to this question: Java Unicode variable names