Type casting inward Java is to cast 1 type, a degree or interface, into only about other type i.e. only about other degree or interface. Since Java is an Object oriented programming linguistic communication too supports both Inheritance too Polymorphism, It’s slow that Super degree reference variable is pointing to SubClass object but the grab hither is that at that topographic point is no way for Java compiler to know that a Superclass variable is pointing to SubClass object. Which way you lot tin non telephone telephone a method which is declared inward the subclass. In lodge to practise that, you lot root involve to cast the Object back into its master copy type. This is called type casting inward Java. You tin type cast both primitive too reference type inward Java. The concept of casting volition live on clearer when you lot volition run into an event of type casting inward side past times side section.
Type casting likewise comes amongst the take chances of ClassCastException inward Java, which is quite mutual amongst a method which accepts Object type too after types cast into to a greater extent than specific type.
We volition run into when ClassCastException comes during type casting and How to avoid it inward coming department of this article. Another worth noting signal hither is that from Java five onwards you lot tin use Generics to write type-safe code to reduce the sum of type casting inward Java which likewise reduces the take chances of java.lang.ClassCastException at runtime.
Type casting likewise comes amongst the take chances of ClassCastException inward Java, which is quite mutual amongst a method which accepts Object type too after types cast into to a greater extent than specific type.
We volition run into when ClassCastException comes during type casting and How to avoid it inward coming department of this article. Another worth noting signal hither is that from Java five onwards you lot tin use Generics to write type-safe code to reduce the sum of type casting inward Java which likewise reduces the take chances of java.lang.ClassCastException at runtime.
What is Type Casting inward Java
From the root paragraph, nosotros pretty much know What is type casting inward Java. Anyway, In uncomplicated words type casting is a procedure of converting one type, which could live on a class or interface to another, But every bit per rules of Java programming language, solely classes or interfaces (collectively known every bit Type) from the same type hierarchy tin live on cast or converted into each other.
If you lot endeavor to cast ii objects which don't portion same type hierarchy, i.e. at that topographic point is no parent-child human relationship between them, you will acquire compile time error. On the other hand, if you lot typecast objects from same type hierarchy but the object which you lot are casting are non of the same type on which you lot are casting too thence it volition throw ClassCastException inward Java.
Some people may inquire why practise you lot involve type casting? well, you lot involve type casting to acquire access to fields too methods declared on target type or class. You tin non access them amongst whatever other type. Let's run into a uncomplicated event of type casting inward Java amongst ii classes Base too Derived which shares same type hierarchy.
If you lot endeavor to cast ii objects which don't portion same type hierarchy, i.e. at that topographic point is no parent-child human relationship between them, you will acquire compile time error. On the other hand, if you lot typecast objects from same type hierarchy but the object which you lot are casting are non of the same type on which you lot are casting too thence it volition throw ClassCastException inward Java.
Some people may inquire why practise you lot involve type casting? well, you lot involve type casting to acquire access to fields too methods declared on target type or class. You tin non access them amongst whatever other type. Let's run into a uncomplicated event of type casting inward Java amongst ii classes Base too Derived which shares same type hierarchy.
Type casting event inward Java
In this Example of type casting inward Java, nosotros receive got ii classes, Base, too Derived. Derived degree extends Base i.e. Base is a Super degree too Derived is a Subclass. So their type hierarchy looks similar the next tree :
Base
|
Derived
Now await at next code :
Base b = new Derived(); //reference variable of Base degree points object of Derived class
Derived d = b; //compile fourth dimension error, requires casting
Derived d = (Derived) b; // type casting Base to Derived
Derived d = b; //compile fourth dimension error, requires casting
Derived d = (Derived) b; // type casting Base to Derived
Above code type casting object of a Derived degree into Base degree too it volition throw ClassCastExcepiton if b is non an object of the Derived class. If Base too Derived degree are non related to each other too doesn't purpose of the same type hierarchy, the cast volition throw compile fourth dimension error. for example, you lot can not cast String too StringBuffer, every bit they are non from same type hierarchy.
See Core Java for Impatient for to a greater extent than details on upcasting too downcasting of objects inward Java. Cay S. Horstmann has explained primal Java concepts inward real prissy way.
Type-casting too ClassCastExcepiton inward Java
As explained inward final department type casting tin consequence inward ClassCastException inward Java. If the object you lot are casting is of unlike type. ClassCastException is quite mutual spell using Java collection framework classes e.g. ArrayList, LinkedList or HashSet etc because they convey object of type java.lang.Object, which allows insertion of whatever object into collection. let's a existent life event of ClassCastException inward Java during type casting :
ArrayList names = new ArrayList();
names.add("abcd"); //adding String
names.add(1); //adding Integer
String cite = (String) names.get(0); //OK
name = (String) names.get(1); // throw ClassCastException because you lot tin non convert Integer to String
names.add("abcd"); //adding String
names.add(1); //adding Integer
String cite = (String) names.get(0); //OK
name = (String) names.get(1); // throw ClassCastException because you lot tin non convert Integer to String
In to a higher house example, nosotros receive got an ArrayList of String which stores names. But nosotros likewise added an wrong cite which is Integer too when nosotros shout out upwards Object from the collection they are of type java.lang.Object which needs to live on cast on respective for performing the operation. This leads into java.lang.ClassCastException, when nosotros endeavor to type, cast the instant object, which is an Integer, into String. This occupation tin live on avoided by using Generics inward Java which we will run into inward side past times side section.
You tin likewise perform casting amongst primitive information types e.g. casting a long variable into an int, casting a double variable into a float, or casting an int variable into char, curt too byte information type. This is known every bit down-casting inward Java. See Core Java, Volume 1 ninth Edition past times Cay S. Horstmann for to a greater extent than details on type casting of primitive too reference type inward Java.
You tin likewise perform casting amongst primitive information types e.g. casting a long variable into an int, casting a double variable into a float, or casting an int variable into char, curt too byte information type. This is known every bit down-casting inward Java. See Core Java, Volume 1 ninth Edition past times Cay S. Horstmann for to a greater extent than details on type casting of primitive too reference type inward Java.
Generics too Type Casting inward Java
Generics was introduced inward Java five along amongst only about other type-safe feature Enum, which ensures type security of code during compile time, So rather you lot getting ClassCastException during runtime past times type casting you lot acquire compile timer fault why your code violate type safety. Use of Generics likewise removes casting from many places e.g. directly spell retrieving an object from Collection you lot don't involve to typecast into respective type. Here is the modified version of same code which is costless of ClassCastException because usage of Generics :
ArrayList<String> names = new ArrayList<String>(); //ArrayList of String solely convey String
names.add("abcd");
names.add(1); //compile fourth dimension fault you lot tin non add together Integer into ArrayList of String
String cite = names.get(0); // no type casting requires
names.add("abcd");
names.add(1); //compile fourth dimension fault you lot tin non add together Integer into ArrayList of String
String cite = names.get(0); // no type casting requires
If you lot are novel to Generics, those angle bracket denotes type. to larn to a greater extent than nearly Generics, See How Generics plant inward Java.
In this Java tutorial, nosotros learn What is type casting inward Java, how to cast 1 degree to only about other degree or interface inward Java amongst a uncomplicated type casting Example. We receive got likewise seen the take chances of ClassCastException related to type casting too How tin nosotros cut down that take chances past times using Generics inward Java. In Summary, minimize type casting inward Java programme too usage type-safe Enum too Generics to cut down or completely eliminate type casting from Java code.
Further Learning
What is Iterator too ListIterator inward Java amongst Example