ClassCastException In Java: In this post, we will discuss ClassCastException. A class cast exception is thrown by Java when you try to cast an Object of one data type to another. Java allows us to cast variables of one type to another if the casting happens between compatible data types.
ClassCastException In Java
As you can see above, the pic ClassCast-Exception exception extends the class RuntimeException and, thus, belongs to those exceptions that can be thrown during the Java Virtual Machine (JVM) operation. It is an unchecked exception; thus, it does not need to be declared in a method’s or a constructor’s throws clause.
java.lang.classcastexception In Java:
An object can be automatically upcasted to its superclass type. You need not mention class type explicitly. But, when an object is supposed to be downcasted to its subclass type, you must explicitly mention the class type. In such a case, a class cast exception is possible. Most of the time, it occurs when you are trying to downcast an object explicitly to its subclass type.
package co.java.exception;
public class ClassCast_Exception
{
public static void main(String[] args)
{
Object obj=new Object();
int i=(int) obj;
System.out.println(i);
}
}
Let’s Run The Above Program:
When we ran the above program, we got the below error:
Exception in thread "main" java.lang.ClassCastException: java.lang.Object cannot be cast to java.lang.Integer at co.java.exception.ClassCastException.main(ClassCast-Exception.java:8)
Let’s take another example:
package co.java.exception;
class Parent {
public Parent() {
System.out.println("An instance of the Parent class was created!");
}
}
final class Child extends Parent {
public Child() {
super();
System.out.println("An instance of the Child class was created!");
}
}
public class ClassCast-ExceptionExample {
public static void main(String[] args) {
Parent p = new Parent();
Child ch = new Child();
ch = (Child) p; //This statement is not allowed.
}
}
If we run the program, then we will get
An instance of the Parent class was created! An instance of the Parent class was created! An instance of the Child class was created! Exception in thread "main" java.lang.ClassCastException: co.java.exception.Parent cannot be cast to co.java.exception.Child at co.java.exception.ClassCastExceptionExample.main(ClassCastExceptionExample.java:20)
Explanation:
In The Above Program, we create an instance of parent and child class. but when we try to assign the parent class instance to the child class instance, that will generate an exception.
