Question

Java beginner here who is terribly confused as to why

1) this is valid:

public class MyArrayOfObjects {

    MyArrayOfObjects[] myArray = new MyArrayOfObjects[5];

    void InstantiateElements (){
        myArray[0] = new MyArrayOfObjects();
    }
}

2) while this is not:

public class MyArrayOfObjects {

    MyArrayOfObjects[] myArray = new MyArrayOfObjects[5];

    myArray[0] = new MyArrayOfObjects();

}

from my understanding, each element of the array of objects is instantiating a MyArrayOfObjects object. So why does option 1 work while 2 does not?

Answer 1

Statements other than variable declarations must occur in:

• Methods
• Constructors
• Initializer blocks

In your second block of code, the statement assigning a value to the first element of the array is not a variable declaration, so it can’t occur directly in the class.

As for why Java is designed this way – to my mind it just makes things simpler. You should put logic to be executed as part of initialization into a constructor. (I would generally try to avoid initializer blocks as well, as it’s easy to forget about them when debugging.)

From section 8.1.6 of the Java Language Specification:

A class body may contain declarations of members of the class, that is, fields (§8.3), classes (§8.5), interfaces (§8.5) and methods (§8.4). A class body may also contain instance initializers (§8.6), static initializers (§8.7), and declarations of constructors (§8.8) for the class.