If you need to create an object in Java you must have a particular class and call its constructor using the "new" keyword (Yes, we can also use a factory method, a creation method, the newInstance method of the class, or other stuff, let's not be pedantic):
public class MyObject {
private String attr1;
private int attr2;
public MyObject(String attr1, int attr2) {
this.attr1 = attr1;
this.attr2 = attr2;
}
public String toString() {
return attr1 + " " + attr2;
}
}
...
MyObject obj = new MyObject(myString, myInt);
System.out.println(obj.toString());
...
In Javascript you simply create an object and add properties and methods to it:personObj = new Object();But the interesting thing comes with methods. If you want to invoke a method in Java it must exist as public (yes, also default, or protected for subclasses, you could use reflection, I'm simplyfing for simplicity's sake!) in a class assignable to the object. In Javascript you simply add it:
personObj.firstname = "John";
personObj.lastname = "Doe";
personObj.age = 50;
personObj.eyecolor = "blue";
addressObj.myOwnMethod = myOwnMethod;If you want to call that method you use the syntax
addressObj.myOwnMethod();BTW, all semicolons at the end of the lines are optional, just to make things weirder. And what happens when you call a method? you are really calling a function defined elsewhere, something like
function myOwnMethod() {
...
}
If your function has parameters, its declaration would be something likefunction myOwnMethod(par1, par2) {
...
}
and if you want to call it you use the syntaxmyObject.myOwnMethod(par1, par2)What if you want to hide the parameters of the function you call, e.g. you ask a shipment for its cost, which is calculated on the basis of some attributes of the shipment itself? In Java you simply ask it to the shipment instance:
double shipmentCost = myShipment.getCost()In Javascript you do the same, but it works in a slightly different way (maybe that's not the only one, but it is the only one I managed to get working). You have a method in the object without parameters, as one would expect, you have a function without parameters, as one would NOT expect, that gets called from the object when you invoke its method and it uses the "this" keyword... The "this" in a function!!! and it does not refer to the function but to the object that invoked it! how counterintuitive!
...It just gives me a headache... it's such a juggling act trying to learn Ajax technologies while keeping your mental health...
// inside the definition of an object (if using a template=
// or simply after the instantiation of an object
myShipment.getShippingCost = getShippingCost
...
// outside the definition of the object
function getShippingCost() {
var cost = 0;
if (this.DestinationAddress == "Boston") {
cost = (this.ShippingType == "STD") ? 100 : 200;
} else if (this.DestinationAddress == "Seoul") {
cost = (this.ShippingType == "STD") ? 500 : 1000;
}
return cost;
}
...
// somewhere else...
myShipment.getShippingCost();
