{"id":1496,"date":"2021-10-06T20:57:10","date_gmt":"2021-10-06T07:57:10","guid":{"rendered":"https:\/\/www.ronella.xyz\/?p=1496"},"modified":"2024-03-06T21:29:54","modified_gmt":"2024-03-06T08:29:54","slug":"pattern-matching-for-instanceof","status":"publish","type":"post","link":"https:\/\/www.ronella.xyz\/?p=1496","title":{"rendered":"Type Pattern Matching for instanceof"},"content":{"rendered":"

The pattern matching enhancement<\/strong> that conditionally extract data<\/strong> from an object if the instanceof operator was satisfied<\/strong> and assigns it to a variable<\/strong>.<\/p>\n

The variable in this pattern matching is following a flow scope<\/strong>. This means that the variable is in scope if it is guaranted that it can satisfies the instanceof operator<\/strong>.<\/p>\n

Code Without Pattern Matching<\/h2>\n
record Person(String firstName, String lastName) {}\n\nRecord rec = new Person("Juan", "Dela Cruz");\n\n\/\/Check if rec is a Person.\nif (rec instanceof Person) {\n\n    \/\/rec can safely be casted to Person.\n    var person = (Person) rec;\n\n    System.out.println(person);\n    System.out.println(person.firstName());\n    System.out.println(person.lastName());\n}<\/code><\/pre>\n
\n
Notice that casting the rec<\/strong> to Person once the check succeded is required<\/strong>.<\/p>\n<\/blockquote>\n
Code With Pattern Matching<\/h2>\n
record Person(String firstName, String lastName) {}\n\nRecord rec = new Person("Juan", "Dela Cruz");\n\n\/\/If rec is a Person extract it to a variable person.\nif (rec instanceof Person person) {\n    System.out.println(person);\n    System.out.println(person.firstName());\n    System.out.println(person.lastName());\n}<\/code><\/pre>\n
\n
Notice that casting is not required<\/strong> here and Person instance is extracted to person variable<\/strong>. Moreover, the scope of the variable<\/strong> is in the truth block<\/strong> of the if statement<\/strong>.<\/p>\n<\/blockquote>\n
Flow Scope<\/h2>\n
Example 1<\/h3>\n
Record rec = new Person("Juan", "Dela Cruz");\n\nif (!(rec instanceof Person person)) {\n    System.out.println("In human.");\n}\nelse {\n    System.out.println(person);\n    System.out.println(person.firstName());\n    System.out.println(person.lastName());\n}<\/code><\/pre>\n
\n
Notice that person variable<\/strong> usage is on the else block<\/strong> of the if statement<\/strong>.<\/p>\n<\/blockquote>\n
Example 2<\/h3>\n
Record rec = new Person("Juan", "Dela Cruz");\n\nif (rec instanceof Person person && "JUAN DELA CRUZ".equals(String.join(person.firstName(), " ", person.lastName().toUpperCase()))) {\n    System.out.println("You won a price");\n}<\/code><\/pre>\n
\n
Notice that the person variable is usable<\/strong> after the AND (&&)<\/em> operator<\/strong>. This is because the and operator guarantees that the instanceof operator was satisfied before evaluating the following condition. Changing it to OR (||)<\/em> operator<\/strong> will be an error, since the person variable is out of scope<\/strong>.<\/p>\n<\/blockquote>\n
Practical Usage<\/h2>\n
equals implementation<\/h3>\n
import java.util.Objects;\n\nrecord Person(String firstName, String lastName) {\n\n    @Override\n    public boolean equals(Object o) {\n        if (this == o) return true;\n        if (null == o) return false;\n        if (o instanceof Person person) {\n            return Objects.equals(firstName, person.firstName()) && Objects.equals(lastName, person.lastName());\n        }\n        return false;\n    }\n\n}<\/code><\/pre>\n","protected":false},"excerpt":{"rendered":"
The pattern matching enhancement that conditionally extract data from an object if the instanceof operator was satisfied and assigns it to a variable. The variable in this pattern matching is following a flow scope. This means that the variable is in scope if it is guaranted that it can satisfies the instanceof operator. Code Without […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":[],"categories":[70],"tags":[],"_links":{"self":[{"href":"https:\/\/www.ronella.xyz\/index.php?rest_route=\/wp\/v2\/posts\/1496"}],"collection":[{"href":"https:\/\/www.ronella.xyz\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.ronella.xyz\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.ronella.xyz\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.ronella.xyz\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=1496"}],"version-history":[{"count":2,"href":"https:\/\/www.ronella.xyz\/index.php?rest_route=\/wp\/v2\/posts\/1496\/revisions"}],"predecessor-version":[{"id":1749,"href":"https:\/\/www.ronella.xyz\/index.php?rest_route=\/wp\/v2\/posts\/1496\/revisions\/1749"}],"wp:attachment":[{"href":"https:\/\/www.ronella.xyz\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=1496"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.ronella.xyz\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=1496"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.ronella.xyz\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=1496"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}