Question

Java’s reflection API is obviously a very powerful tool, but not particularly object-oriented. What are some situations where it is appropriate (and conversely, inappropriate) to use reflection?

Answer 1

In my opinion…

Appropriate (clean):

• Instantiating root of a dynamically-loaded implementation, such as an applet.
• Use of Proxy to create a proxy or a mock implementation (may be better at compile time).
• Implementing interpreters that allow unrestricted access to the Java libraries. (Note, from a security perspective the interpreted code now has the effective privileges as the interpreter – can be kind of dangerous.)

Appropriate hacks:

• Circumventing Java language access controls in third party code where you absolutely have to.
• Implementing a “cross-cutting concern” such as persistence.
• Removing static dependencies that load classes causing slower start up.

Inappropriate:

• General circumventing Java language access controls (includes testing).
• Anything the relies upon Java language access rights given by the particular reflection-calling class.
• Anywhere where implementing an interface would work.

Generally reflection is much easier than generating source which is much easier than creating bytecode.