Effective Java 53 Prefer interfaces to reflection

Disadvantage of reflection

1. You lose all the benefits of compile-time type checking, including exception checking.
2. The code required to perfrom reflective access is clumsy and verbose.
3. Peformance suffers.

When to use reflecition

Design time - Component-based application builider tools which load classes on demand and use reflection to find out what methods and constructors they support.

When at compile time an appropriate interface or super class by which to refer to the class(Item 52) which is unavailable at compile time.

1. Class browers.
2. Object inspectors.
3. Code analysis tools.
4. Interpretive embedded systems.
5. Remote procedure call(RPC) systems to eliminate the need of stub compilers.
6. Use of reflection is to manage a class's dependencies on other classes, methods, or fields that may be absent at runtime.
7. Service provider framework(Item 1).

// Reflective instantiation with interface access

public static void main(String[] args) {

// Translate the class name into a Class object

Class<?> cl = null;

try {

cl = Class.forName(args[0]);

} catch(ClassNotFoundException e) {

System.err.println("Class not found.");

System.exit(1);

}

// Instantiate the class

Set<String> s = null;

try {

s = (Set<String>) cl.newInstance();

} catch(IllegalAccessException e) {

System.err.println("Class not accessible.");

System.exit(1);

} catch(InstantiationException e) {

System.err.println("Class not instantiable.");

System.exit(1);

}

// Exercise the set

s.addAll(Arrays.asList(args).subList(1, args.length));

System.out.println(s);

}

When not to use reflection

1. Objects should not be accessed reflectively in normal applications at runtime.
2. If the appropriate constructor has no parameters, then you don't even need to use java.lang.reflect; the Class.newInstance method provides the required functionality.

Summary

Reflection is a powerful facility that is required for certain sophisticated system programming tasks, but it has many disadvantages. If you are writing a program that has to work with classes unknown at compile time, you should, if at all possible, use reflection only to instantiate objects, and access the objects using some interface or superclass that is known at compile time.