I have an Object in java. Is there a way to check if an object is an instance of a String, HashMap, or HashMap[ ] before actually casting it to those objects?
If not, as it seems counterintuitive that the above would work, is there a way to cast it into each object, and test something about the newly casted object to see if its in fact the type of object into which it was casted?
Yes:
if(obj instanceof String)
{
String str = (String) obj;
.
.
.
}
By the way, to clarify regarding this:
[…] test something about the newly casted object to see if its in fact the type of object into which it was casted?
You cannot cast something into an invalid type. If obj has type String, then ((Integer)obj) will cause a ClassCastException to be raised at run-time.
instanceof returns false when obj is null
Object[]. You can use System.out.println(java.util.Arrays.toString((Object[]) ____)), where ____ is the variable-name, to print out the elements of the array.
You are looking for the instanceof operator.
The instanceof operator compares an object to a specified type. You can use it to test if an object is an instance of a class, an instance of a subclass, or an instance of a class that implements a particular interface.
Example: "Hello" instanceof String would return true while new Integer(5) instanceof String would return false.
instanceofyou can always, of course, cast to the presumed object type and listen for theClassCastException.objisnull, then(obj instanceof ____)will befalse, but((____) obj)will not cause an exception to be raised.instanceof. You're checking to see if you have a String, a HashMap, or a HashMap array? Where's the abstraction and information hiding in that? Java's an object-oriented language. I don't know what problem you're solving, but it sounds like you're lost. You should think of a better abstraction than this.instanceof, just pointing out that it would work too.)