Question

I’m studying Prototype Design pattern I can’t understand the syntax below. Can you explain it to me? What does it mean for a class to be put in parentheses and initialized like this :

Person person2 = (Person) person1.doSomthing();

Code in context:

// code in  int main
Person person1 = new Person("Fred");// this is understood
    System.out.println("person 1:" + person1);// this is understood
    Person person2 = (Person) person1.doClone();//not understood
    System.out.println("person 2:" + person2);// this is understood

Is this syntax in java for casting?

Answer 1

It is a cast. In other words, the doSomething() method is most likely not declared to return a Person. So you need to first cast the returned value to a Person before assigning it to person2.

If doSomething does return a Person, then the cast is not necessary.

And if the actual type of the object returned by doSomething is not assignable to a Person, the cast will throw a ClassCastException at runtime.

More info about it in the JLS #15.16:

A cast expression converts, at run-time, a value of one numeric type to a similar value of another numeric type; or confirms, at compile-time, that the type of an expression is boolean; or checks, at run-time, that a reference value refers to an object whose class is compatible with a specified reference type.

The parentheses and the type they contain are sometimes called the cast operator.