Question

In PHP, to create a new object you would do something like this, $dog = new Dog;. But in Java you would do something like, Dog x = new Dog; or Dog x;. Could someone explain why you need to say the Dog class in front of the variable?

Answer 1

Java statically and explicitly typed.

The type of the variable may be different from the type of the value it holds, due to inheritance. For example:

Animal dog = new Dog();

Here the type of the dog variable is Animal, but the value it holds is a reference to an instance of Dog.

Now in some other languages (C# 3 being the obvious example as a near neighbour of Java) you can use implicitly typed local variables when you actually want the type of a local variable to be the same as the type of the expression used to initialize it:

var dog = new Dog(); // Equivalent to Dog dog = new Dog();

(The type inferencing capabilities of some other statically typed languages go well beyond this.)

So, to go back to your original question, the answer is:

• The dog variable has a type which is known at compile-time; this isn’t true in PHP
• The type of the variable has to be explicitly stated in Java; this is related to static typing, but isn’t a requirement of static typing