{"id":6563,"date":"2024-04-21T23:57:28","date_gmt":"2024-04-22T06:57:28","guid":{"rendered":"https:\/\/zentut.com\/java-tutorial\/java-casting\/"},"modified":"2024-04-21T23:58:35","modified_gmt":"2024-04-22T06:58:35","slug":"java-casting","status":"publish","type":"page","link":"https:\/\/www.zentut.com\/java-tutorial\/java-casting\/","title":{"rendered":"Java Casting"},"content":{"rendered":"\n

Summary<\/strong>: in this tutorial, you will learn how to use Java casting that convert an object of a class to another.<\/p>\n\n\n\n

Introduction to Java Casting<\/h2>\n\n\n\n

In Java, casting is a technique that converts an object of a class<\/a> into another. Casting allows you to access fields and methods that are specific to a target class.<\/p>\n\n\n\n

Technically, you should only use casting when there is an actual relationship between the classes in the class hierarchy. It means you can only cast an object of classes that have a superclass-subclass relationship<\/a>.<\/p>\n\n\n\n

If you attempt to cast unrelated classes, you will encounter an error runtime. More specifically, you’ll get an ClassCastException<\/code>.<\/p>\n\n\n\n

Java supports two types of object castings: upcasting and downcasting.<\/p>\n\n\n\n

Upcasting<\/h3>\n\n\n\n

Upcasting converts an object of a subclass to its superclass:<\/p>\n\n\n

Superclass object = new<\/span> Subclass(); \/\/ upcasting<\/span><\/code><\/span>Code language:<\/span> Java<\/span> (<\/span>java<\/span>)<\/span><\/small><\/pre>\n\n\n
In this syntax, we create a new object of a subclass and assign it to a reference variable with the type of Superclass. The upcasting is always safe and doesn’t require an explicit cast.<\/p>\n\n\n\n
In the following syntax, we assign an instance of a subclass to a reference of a superclass:<\/p>\n\n\n
Superclass object = subclassObject; \/\/ upcasting<\/span><\/code><\/span>Code language:<\/span> Java<\/span> (<\/span>java<\/span>)<\/span><\/small><\/pre>\n\n\n
Downcasting<\/h3>\n\n\n\n
Downcasting is the casting of an object of a superclass to a subclass:<\/p>\n\n\n
Subclass subObj = (Subclass) superObj; \/\/ Downcasting<\/span><\/code><\/span>Code language:<\/span> Java<\/span> (<\/span>java<\/span>)<\/span><\/small><\/pre>\n\n\n
Note that you can only perform a downcasting if the original object is of the subclass type. And you need to use parentheses and the subclass type.<\/p>\n\n\n\n
For safety, you can use the instanceof<\/code> operator to check if the object being downcasted is an instance of the Subclass:<\/p>\n\n\n
if<\/span> (obj instanceof<\/span> Subclass) {\n    Subclass subObj = (Subclass) obj; \/\/ Downcast only if safe<\/span>\n}<\/code><\/span>Code language:<\/span> Java<\/span> (<\/span>java<\/span>)<\/span><\/small><\/pre>\n\n\n
Java casting example<\/h2>\n\n\n\n
Suppose you have two classes, Person<\/code> and Employee<\/code>. The Employee<\/code> class is a subclass of the Person<\/code> class.<\/p>\n\n\n
\/\/ Person.java<\/span>\nclass<\/span> Person<\/span> <\/span>{\n  \/\/ ...<\/span>\n}\n\n\/\/ Employee.java<\/span>\nclass<\/span> Employee<\/span> extends<\/span> Person<\/span> <\/span>{\n  \/\/ ...<\/span>\n}<\/code><\/span>Code language:<\/span> Java<\/span> (<\/span>java<\/span>)<\/span><\/small><\/pre>\n\n\n
The following example illustrates how to perform an upcasting that converts an object of the Employee<\/code> class to the Person<\/code> class:<\/p>\n\n\n
Person person = new<\/span> Employee();<\/code><\/span>Code language:<\/span> Java<\/span> (<\/span>java<\/span>)<\/span><\/small><\/pre>\n\n\n
In this case, the person<\/code> object can access only fields and methods of the Person<\/code> class. And the person<\/code> object cannot access the fields and methods defined in the Employee<\/code> class.<\/p>\n\n\n\n
The following example shows how to perform a downcasting that converts <\/p>\n\n\n
Person person = new<\/span> Employee();\nif<\/span> (person instanceof<\/span> Employee) {\n    Employee employee = (Employee) person;\n}<\/code><\/span>Code language:<\/span> Java<\/span> (<\/span>java<\/span>)<\/span><\/small><\/pre>\n\n\n
Because it is a downcasting, we use the instanceof<\/code> operator to ensure that the person<\/code> is an instance of the Employee<\/code> class and use explicit cast by placing the Employee<\/code> class in parentheses.<\/p>\n\n\n\n
Because of downcasting, the employee can access the fields and methods defined in the Employee<\/code> class.<\/p>\n\n\n\n
Summary<\/h2>\n\n\n\n
    \n
  • Use Java casting to convert an object of one class to another, within the class hierarchy.<\/li>\n\n\n\n
  • Use downcasting to convert an object of a superclass to its subclass.<\/li>\n\n\n\n
  • Use upcasting to convert an object of a subclass to its superclass.<\/li>\n<\/ul>\n","protected":false},"excerpt":{"rendered":"
    In this tutorial, you will learn how to use Java casting that converts an object of a class to another.<\/p>\n","protected":false},"author":2,"featured_media":0,"parent":2190,"menu_order":40,"comment_status":"closed","ping_status":"closed","template":"","meta":{"footnotes":""},"class_list":["post-6563","page","type-page","status-publish","hentry"],"_links":{"self":[{"href":"https:\/\/www.zentut.com\/wp-json\/wp\/v2\/pages\/6563","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.zentut.com\/wp-json\/wp\/v2\/pages"}],"about":[{"href":"https:\/\/www.zentut.com\/wp-json\/wp\/v2\/types\/page"}],"author":[{"embeddable":true,"href":"https:\/\/www.zentut.com\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/www.zentut.com\/wp-json\/wp\/v2\/comments?post=6563"}],"version-history":[{"count":2,"href":"https:\/\/www.zentut.com\/wp-json\/wp\/v2\/pages\/6563\/revisions"}],"predecessor-version":[{"id":6566,"href":"https:\/\/www.zentut.com\/wp-json\/wp\/v2\/pages\/6563\/revisions\/6566"}],"up":[{"embeddable":true,"href":"https:\/\/www.zentut.com\/wp-json\/wp\/v2\/pages\/2190"}],"wp:attachment":[{"href":"https:\/\/www.zentut.com\/wp-json\/wp\/v2\/media?parent=6563"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}