Why we need to put the "()" at the end of a declaration of an instance?

Question

Example:
Person p1 = new Person();

And what's its purpose?

Answer 1

In Java, the "new" keyword is used to call a class's constructor method. You can define a constructor method for a class by naming the method with the same identifier as the class. Example:

class Number {
int value;
Number(int x) { //the constructor method
value = x;
}
}

In this example, the constructor needs an integer argument, so I would call it like this:

Number x = new Number(42);

However, in Java, if you don't write the constructor for a class it is given a default constructor which initializes all of the fields to their default value (Ex: an int would be initialized to 0; a String would be initialized to null). However, it is important to remember that this default constructor, although it accepts zero arguments, is still a method. Since it's a method, it must be called with parenthesis.