Why cannot cast Integer to String in java?
JavaStringCastingIntegerJava Problem Overview
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.
Java Solutions
Solution 1 - Java
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.
Solution 2 - Java
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.
Solution 3 - Java
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();
Solution 4 - Java
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.
Solution 5 - Java
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.
Solution 6 - Java
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.
Solution 7 - Java
You should call myIntegerObject.toString() if you want the string representation.
Solution 8 - Java
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
.
Solution 9 - Java
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)
|
(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 {}
> (A)
/ <br>(B1) (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:
> (Object)
/ <br>(Integer) (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
Solution 10 - Java
It returns a string representation of integer.
Solution 11 - Java
Use .toString instead like below:
String myString = myIntegerObject.toString();