Why cannot cast Integer to String in java

Question

I found some strange exception   java lang ClassCastException  java lang Integer   cannot be cast to java lang String   How it can be possible  Each object can be casted to String  doesn t it   The code is   String myString    String  myIntegerObject    Thanks

User · Accepted Answer

Why this is not possible   Because String and Integer are not in the same Object hierarchy         Object                              String     Integer   The casting which you are trying  works only if they are in the same hierarchy  e g         Object                 A        B   In this case   A  objB or  Object  objB or  Object  objA will work   Hence as others have mentioned already  to convert an integer to string use    String valueOf integer   or Integer toString integer  for primitive    or   Integer toString   for the object

User · Answer

Objects can be converted to a string using the toString   method   String myString   myIntegerObject toString      There is no such rule about casting  For casting to work  the object must actually be of the type you re casting to

User · Answer

Casting is different than converting in Java  to use informal terminology   Casting an object means that object already is what you re casting it to  and you re just telling the compiler about it  For instance  if I have a Foo reference that I know is a FooSubclass instance  then  FooSubclass Foo tells the compiler   don t change the instance  just know that it s actually a FooSubclass   On the other hand  an Integer is not a String  although  as you point out  there are methods for getting a String that represents an Integer  Since no no instance of Integer can ever be a String  you can t cast Integer to String

User · Answer

Use  toString instead like below   String myString   myIntegerObject toString

User · Answer

For int types use   int myInteger   1  String myString   Integer toString myInteger     For Integer types use   Integer myIntegerObject   new Integer 1   String myString   myIntegerObject toString

User · Answer

You can t cast explicitly anything to a String that isn t a String  You should use either        myInt    or   Integer toString myInt     or   String valueOf myInt     I prefer the second form  but I think it s personal choice   Edit OK  here s why I prefer the second form  The first form  when compiled  could instantiate a StringBuffer  in Java 1 4  or a StringBuilder in 1 5  one more thing to be garbage collected  The compiler doesn t optimise this as far as I could tell  The second form also has an analogue  Integer toString myInt  radix  that lets you specify whether you want hex  octal  etc  If you want to be consistent in your code  purely aesthetically  I guess  the second form can be used in more places   Edit 2 I assumed you meant that your integer was an int and not an Integer  If it s already an Integer  just use toString   on it and be done

User · Answer

In your case don t need casting  you need call toString     Integer i   33  String s   i toString      or s   String valueOf i     or s        i    Casting  How does it work   Given   class A    class B extends A          A      nbsp  nbsp   B    B b   new B      no cast A a   b     upcast with no explicit cast a    A b    upcast with an explicit cast b    B a    downcast   A and B in the same inheritance tree and we can this   a   new A    b    B a      again downcast  Compiles but fails later  at runtime  java lang ClassCastException   The compiler must allow things that might possibly work at runtime  However  if the compiler knows with 100  that the cast couldn t possibly work  compilation will fail  Given   class A    class B1 extends A    class B2 extends A          nbsp  nbsp  nbsp  nbsp  nbsp  nbsp  nbsp  nbsp  A      nbsp  nbsp  nbsp  nbsp  nbsp  nbsp   nbsp  nbsp  nbsp  nbsp  nbsp  nbsp  nbsp   B1  nbsp  nbsp  nbsp  nbsp  nbsp  nbsp  nbsp  B2    B1 b1   new B1    B2 b2    B2 b1     B1 can t ever be a B2   Error  Inconvertible types B1 and B2  The compiler knows with 100  that the cast couldn t possibly work  But you can cheat the compiler   B2 b2    B2  A b1    but anyway at runtime   Exception in thread  main  java lang ClassCastException  B1 cannot be cast to B2  in your case       nbsp  nbsp  nbsp  nbsp  nbsp  nbsp  nbsp  nbsp  nbsp  nbsp  Object  nbsp  nbsp  nbsp  nbsp  nbsp  nbsp  nbsp  nbsp  nbsp  nbsp  nbsp  nbsp   nbsp  nbsp  nbsp  nbsp  nbsp  nbsp  nbsp   Integer  nbsp  nbsp  nbsp  nbsp  nbsp  nbsp  nbsp  String    Integer i   33    String s    String i  - compiler error String s    String  Object i    at runtime  Exception in thread  main  java lang ClassCastException  java lang Integer cannot be cast to java lang String

User · Answer

No  Integer and String are different types  To convert an integer to string use  String valueOf integer   or Integer toString integer  for primitive  or Integer toString   for the object

User · Answer

No  Every object can be casted to an java lang Object  not a String  If you want a string representation of whatever object  you have to invoke the toString   method  this is not the same as casting the object to a String

User · Answer

You should call myIntegerObject toString   if you want the string representation

User · Answer

Use String valueOf integer    It returns a string representation of integer

[java] Why cannot cast Integer to String in java?

Examples related to java

Examples related to string

Examples related to casting

Examples related to integer