Java – Why is Class.newInstance() “evil”

constructorinstantiationjavaruntime

Ryan Delucchi asked here in comment #3 to Tom Hawtin's answer:

why is Class.newInstance() "evil"?

this in response to the code sample:

// Avoid Class.newInstance, for it is evil.
Constructor<? extends Runnable> ctor = runClass.getConstructor();
Runnable doRun = ctor.newInstance();

so, why is it Evil?

Best Solution

The Java API documentation explains why (http://java.sun.com/javase/6/docs/api/java/lang/Class.html#newInstance()):

Note that this method propagates any exception thrown by the nullary constructor, including a checked exception. Use of this method effectively bypasses the compile-time exception checking that would otherwise be performed by the compiler. The Constructor.newInstance method avoids this problem by wrapping any exception thrown by the constructor in a (checked) InvocationTargetException.

In other words, it can defeat the checked exceptions system.