I am trying to understand generics and interfaces and I came across this code:
Func<Integer, Integer> fDouble = new Func<Integer, Integer>()
{
public Integer apply(Integer x)
{
return x * x;
}
};
I understood that the method fDouble returns the double of the inputted integer, however, I cannot understand how there is a ; after the } and how the method is declared by
Func<Integer, Integer> fDouble = new Func<Integer, Integer>()
The code is creating an anonymous class which implements the Func<Integer, Integer> interface. The supplied link is a Java tutorial which should help you understand the syntax.
The ; is there because the code is declaring a variable fDouble and storing in that variable a reference to a newly-created object of the anonymous class.
This is actually a case of an anonymous class, which is a way to create a class without giving it an explicit name. An anonymous class can be created by extending a class or by implementing an interface. The syntax for an anonymous class that implements an interface is:
MyInterface object = new MyInterface() {
/* override or implement methods here */
};
The semicolon is required, like it is required after every statement in Java.
class Square implements Func<Integer, Integer> { ... } and then use it normally: Func<Integer, Integer> fDouble = new Square();Square.Actually, it is called Anonymous inner class. Also, it is better to specify like this:
interface Func<T extends Number>{
T measureShape(T t);
}
Because if you work with data which can be any type from Number interface, you should use bounded type. So now, you can use it with Integers or Double. Also anonymous class just implements Func interface and creates it's instance.
fDouble. Whoever wrote that should be forced to do 20 pushups, then rename it. :-)