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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?
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Class. newInstance() throws any exception thrown by the constructor, regardless of whether it is checked or unchecked. Constructor. newInstance() always wraps the thrown exception with an InvocationTargetException .
These calls can be replaced with a call to clazz. getDeclaredConstructor(). newInstance(). The reason for the deprecation is that that path bypasses compile-time exception checking.
newInstance() creates a new instance of the class represented by this Class object. The class is instantiated as if by a new expression with an empty argument list. The class is initialized if it has not already been initialized. .
Reflection is a feature in the Java programming language. It allows an executing Java program to examine or "introspect" upon itself, and manipulate internal properties of the program. For example, it's possible for a Java class to obtain the names of all its members and display them.
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.newInstancemethod 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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