What is the difference between the new operator and Class.newInstance()?

java reflection new-operator
i2ijeya picture i2ijeya · Jan 6, 2011 · Viewed 26.1k times · Source

What is the difference between new operator and Class.forName(...).newInstance()? Both of them create instances of a class, and I'm not sure what the difference is between them.

Answer

templatetypedef picture templatetypedef · Jan 6, 2011

The new operator creates a new object of a type that's known statically (at compile-time) and can call any constructor on the object you're trying to create. It's the preferred way of creating an object - it's fast and the JVM does lots of aggressive optimizations on it.

Class.forName().newInstance() is a dynamic construct that looks up a class with a specific name. It's slower than using new because the type of object can't be hardcoded into the bytecode, and because the JVM might have to do permissions checking to ensure that you have the authority to create an object. It's also partially unsafe because it always uses a zero-argument constructor, and if the object you're trying to create doesn't have a nullary constructor it throws an exception.

In short, use new if you know at compile-time what the type of the object is that you want to create. Use Class.forName().newInstance() if you don't know what type of object you'll be making.

Related questions

Java: newInstance of class that has no default constructor

I'm trying to build an automatic testing framework (based on jUnit, but that's no important) for my students' homework. They will have to create constructors for some classes and also add some methods to them. Later, with the testing functions …

Read More
What could cause java.lang.reflect.InvocationTargetException?

Well, I've tried to understand and read what could cause it but I just can't get it: I have this somewhere in my code: try{ .. m.invoke(testObject); .. } catch(AssertionError e){ ... } catch(Exception e){ .. } Thing is that, when it tries …

Read More
How do I invoke a Java method when given the method name as a string?

If I have two variables: Object obj; String methodName = "getName"; Without knowing the class of obj, how can I call the method identified by methodName on it? The method being called has no parameters, and a String return value. It's …

Read More