Question

If I define a class like following:

public class myClass {
    private x = new anotherClass();
    private y;

    public myClass() {
        y = new anotherClass();
    } 
}

which variable will get instance earlier? x or y?

And, is it unrecommended to assign a variable outside the constructor?

Answer 1

The order of execution is:

• Superclass constructor (or chained constructor to the same class)
• Instance variable initializers (the expression assigning to x in your code)
• Constructor body (the statement assigning to y in your code)

Section 12.5 of the Java Language Specification contains the details.

Whether you assign the variable in the constructor or not is up to you – I quite like a rule of thumb whereby if the initial value doesn’t depend on any constructor parameters, and will always be the same for all constructors, use a variable initializer. Otherwise, assign it in a constructor.