Why is Class.newInstance() "evil"?

java constructor runtime instantiation
Amir Arad picture Amir Arad · Oct 12, 2008 · Viewed 70k times · Source

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?

Answer

Chris Jester-Young picture Chris Jester-Young · Oct 12, 2008

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.

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