Programming Perl, 4th Edition

Java Traps

• There is no main in Perl or, rather, no:

  public static void main(String[ ] argv) throws IOException

• Perl allocates memory for you as you need it by growing its arrays and hashes on demand. Autovivification means that if you assign to it, there’ll be room for it.

• Perl doesn’t make you declare your variables in advance unless you use strict.

• In Perl, there is a difference between a thing and a reference to a thing, so you (usually) have to explicitly dereference the latter.

• Not all functions need to be methods in Perl.

• String and numeric literals aren’t usually objects in Perl—but they can be.

• Java programmers looking to define a data structure using a class may be surprised that Perl builds these up out of simple data declarations mixing anonymous hashes and arrays. See Chapter 9.

• Instance data on a Perl object is (usually) just a value in the hash used for the object, where the name of that hash field corresponds to the name of instance data in Java.

• Privacy is optional in Perl.

• The function that a method invocation ends up calling is not determined until runtime, and any object or class with a method by that name is just fine by Perl. Only the interface matters.

• Perl supports operator overloading.

• Perl does not support function overloading by signature. See the Class::Multimethod module on CPAN.

• Perl allows multiple inheritance, although this more corresponds to multiple interfaces in Java, since Perl classes inherit only methods, not data.

• A Java char is not an abstract Unicode codepoint; ...