Does it make sense to define a final String in Jav

问题:

Possible Duplicate:
String and Final

From http://docs.oracle.com/javase/6/docs/api/java/lang/String.html I can read that:

Strings are constant; their values cannot be changed after they are created. 

Does this mean that a final String does not really make sense in Java, in the sense that the final attribute is somehow redundant?

回答1:

The String object is immutable but what it is is actually a reference to a String object which could be changed.

For example:

String someString = "Lala";

You can reassign the value held by this variable (to make it reference a different string):

someString = "asdf";

However, with this:

final String someString = "Lala";

Then the above reassignment would not be possible and would result in a compile-time error.

回答2:

final refers to the variable, not the object, so yes, it make sense.

e.g.

final String s = "s";
s = "a"; // illegal

回答3:

It makes sense. The final keyword prevents future assignments to the variable. The following would be an error in java:

final String x = "foo";
x = "bar" // error on this assignment

回答4:

References are final, Objects are not. You can define a mutable object as final and change state of it. What final ensures is that the reference you are using cannot ever point to another object again.