instanceof.md

instanceof

If you have an Object you can recover the actual type of the data stored in it using instanceof.

~void main() {
Object o = "123";

if (o instanceof String) {
    System.out.println("This object is a String!");
}
~}

Inside an if you give the name of a field or variable whose type is Object. Then you write instanceof followed by the type you want to see if that object is an instance of.

You can also give a variable name after the type. This will let you call methods from the actual type that are otherwise unavailable when all Java knows is that you have an Object.

~void main() {
Object o = "123";

if (o instanceof String s) {
    System.out.println(
        "Can call String methods after recovering the type: " + s.charAt(0)
    );
}
~}