Casting to String or using String.valueOf() in Java [duplicate]

Question

This morning I found an interesting question --- cast object to string check if valid and I found there are two types of answers. One is to cast an object to String, the other one is to get the string representation of that object instead (eg. using String.valueOf() or toString()). My questions are: what is the best practice? what is the difference between them?

Before I asked this questions, I found several existing questions which are relevant, but I didn't find one which answers my question. Please forgive me if I missed the important one and hope you don't mind pointing me to the answers.

Thank you,

IMO I would go the secure way and use instanceof. Executing toString in a String object seems redundant and if the object reference is not a String and haven't overridden the toString method it could lead to unknown behavior. — Luiggi Mendoza
– Luiggi Mendoza, Commented Jun 10, 2013 at 17:41
@LuiggiMendoza, thank you for your fast response. Can I further know why it is regarded as a more secure way? Or why is the valueOf function is insecure? — keelar
– keelar, Commented Jun 10, 2013 at 17:42

assylias · Accepted Answer · 2013-06-10 17:42:34Z

12

If the Object is not a String, a cast will throw a ClassCastException at runtime. For example:

Object o = new Object();
String s = (String) o; //Exception here

The difference between the other two solutions (toString vs. String.valueOf) is in the case of a null object. toString will throw an exception whereas String.valueOf() will simply return "null":

Object o = null;
String s = String.valueOf(o); //s = "null";
String t = o.toString(); //NullPointerException

answered Jun 10, 2013 at 17:42

assylias

330k84 gold badges680 silver badges806 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

keelar Over a year ago

Thank you very much for you answer. I am sorry that I can't vote up for now as I have reached the daily limit, I will certainly vote up once I can. So in your answer you tells the difference between casting and using functions. Can I know which one (casting or converting) is better in practice? or the answer depends on the use cases? Thank you.

assylias Over a year ago

@keelar If you are 100% sure that you have a String, casting is fine (for example after an if(o instanceof String) check). If you don't know and just want a String representation of some random object, you should use toString or String.valueOf (depending on the desired behaviour in case of a null string).

Collectives™ on Stack Overflow

Casting to String or using String.valueOf() in Java [duplicate]

1 Answer 1

2 Comments

Linked

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

2 Comments

Linked

Related