Class Cast Exception

[Ravi Tripura]

Hi,
I got a "java.lang.ClassCastException" when I try to do the following:

  
 
Vector v = new Vector();
StringBuffer s = new StringBuffer("MyName");
v.addElement(s);
 
                Integer someint = (Integer)myvector.get(0);
 

I understood that this Exception is thrown because of the fact that Cast should have been '(String)'.

But can any one tell me if the 'get()' method of Vector returns 'a simple Java Object', why doesn't the compiler allow '(Integer)' that extends a Java Object?
How does the JRE determines the type of Cast allowed ?

thanks in advance,

Ravi.

[Ernest Friedman-Hill]

First, the cast shouldn't be (String), it should be (StringBuffer), of course.

Second, a cast of a reference type is only a hint to the compiler that an object is of a certain type; it's not a conversion operator. The real object in the Vector is a StringBuffer, and not an Integer, so it can't be cast to Integer. It's as simple as that.

The JVM "knows" the real type of every object; the details are implementation specific, but generally every object will contain a reference to its Class object or a data structure representing its Class.

[Ravi Tripura]

Originally posted by Ravi Tripura:
Hi,
I got a "java.lang.ClassCastException" when I try to do the following:

  
 
Vector v = new Vector();
StringBuffer s = new StringBuffer("MyName");
v.addElement(s);
 
                Integer someint = (Integer)myvector.get(0);
 

I understood that this Exception is thrown because of the fact that Cast should have been '(String)'.

But can any one tell me if the 'get()' method of Vector returns 'a simple Java Object', why doesn't the compiler allow '(Integer)' that extends a Java Object?
How does the JRE determines the type of Cast allowed ?

thanks in advance,

Ravi.

Hi Ernest,

I have added the following statement to my code:

System.out.println(v.get(0).getClass());

and got the class type information of the object.

thanks very much for the information,

Ravi.