You could implement the Visitor pattern. Detailed Answer The idea is to use polymorphism to perform the type-checking. Each subclass overrides the accept(Visitor) method, which should be declared in the superclass. When we have a situation like: void add(Vehicle vehicle) { //what type is vehicle?? } We can pass an object into a method declared … Read more
There’s very little practical use for String objects as created by new String(“foo”). The only advantage a String object has over a primitive string value is that as an object it can store properties: var str = “foo”; str.prop = “bar”; alert(str.prop); // undefined var str = new String(“foo”); str.prop = “bar”; alert(str.prop); // “bar” … Read more
Yes, they do the same thing, both traverse up the prototype chain looking for an specific object in it. The difference between both is what they are, and how you use them, e.g. the isPrototypeOf is a function available on the Object.prototype object, it lets you test if an specific object is in the prototype … Read more
This: ” ” + obj instanceof Object is evaluated as: (” ” + obj ) instanceof Object and ” ” + obj is indeed a non-null string which is an instance of Object.
For a polymorphic switch with instanceof which considers inheritance: switch(true) { case $objectToTest instanceof TreeRequest: echo “tree request”; break; case $objectToTest instanceof GroundRequest: echo “ground request”; break; } For a switch where the class name should match exactly: $class = get_class($objectToTest); switch($class) { case ‘TreeRequest’: echo “tree request”; break; case ‘GroundRequest’: echo “ground request”; break; … Read more
You could try instanceofDocs… if ($var instanceof DateTime) { // true } See also is_aDocs: if (is_a($var, ‘DateTime’)) { // true }
If you have to do this, the only way would be the getClass().equals(Foo.class) option you’ve suggested. However, the goal of OO design is to allow you to treat any Foo in the same fashion. Whether or not the instance is a subclass should be irrelevant in a normal program.
use typeof “foo” === “string” instead of instanceof.
A related issue that I have come across recently (and which led me to this page, before I figured out what was going on) is that the Eclipse environment can report “Incompatible conditional operand types” in an ‘instanceof’ expression erroneously due to a missing ‘import’ statement for the type on the right of the ‘instanceof’. … Read more
Yes, it would. And why should it not? Because child is in fact an instance of Parent. If, you want to perform an operation only for a child you should check if (child instanceof Child){ } However you should remember the following statement from Effective C++, by Scott Meyers : “Anytime you find yourself writing … Read more