Why cast after an instanceOf?

by

Old code will not work correctly

The implied cast feature is justified after all but we have trouble to implement this FR to java because of backward-compatibility.

See this:

public class A {
    public static void draw(Square s){...} // with implied cast
    public static void draw(Object o){...} // without implied cast
    public static void main(String[] args) {
        final Object foo = new Square();
        if (foo instanceof Square) {
            draw(foo);
        }
    }
}

The current JDK would compile the usage of the second declared method.
If we implement this FR in java, it would compile to use the first method!

🔴 JDK 14

We finally implemented this feature in JDK 14. As you might have noticed you can declare a new variable within the instanceof-linkage. This new variable has been defined by the value of a automatically downcast to the specified type.

if (any instanceof String s) {
  System.out.println(s);
}

Leave a Comment

tech