Use of the Java instanceof operator

Usage:

(type variable instanceof class | interface)

Function:

The instanceof operator is used to determine whether the preceding object is a subsequent class or an instanceof its subclass or implementation class. Returns true if yes or false.

Note:

, the compile-time type of the operands preceding instanceof is either the same as the following class or has a parent-child inheritance relationship with the latter class or it will cause a compilation error.

A simple example:

public class TestInstanceof {
    public static void main(String[] args) {
        //When you declare hello using the Object class, the compile type of hello is Object
        //The Object class is the parent of all classes, but the actual type of hello is String
        Object hello = "Hello";

        //String is a subclass of Object and you can do the instanceof operation and return true
        System.out.println(" Is the string object Class instance: "
                + (hello instanceof Object));

        //true
        System.out.println(" Is the string String Examples: "
                + (hello instanceof String));

        //false
        System.out.println(" is the string an instance of the Math class:"
                + (hello instanceof Math));

        //String implements the Comparable interface, so it returns true
        System.out.println(" Is the string Comparable Class instance: "
                +(hello instanceof Comparable));

        
        //String a = "hello";
        //System.out.println(" is the string an instance of the Math class:"
        //        + (a instanceof Math));

    }
}

Operation results:

 Is the string object Class instance: true
 Is the string String Examples: true
 Is the string Math Class instance: false
 Is the string Comparable Class instance: true

Typically, before casting, the code is robust by determining whether the previous object is an instance of the next object and whether it can be successfully converted.