Question

I have a question on page 128 of Bruce Eckel’s Thinking In Java 4th Edition, the second paragraph, the last sentence it asks:

what would happen if an overloaded constructor were defined that did not initialize w3 and there wasn’t a “default” initialization for w3 in its definition?

I found this statement is confusing to understand, could experts or readers of this book help me a little? Thanks!

Answer 1

Window w3 = new Window(3);

It is just guarding if someone does not initialize w3 properly in the overloaded constructor. Such field instantiation is automatically put at the beginning of each constructor. So even the overloaded one will receive the w3 initialization.

If you declare only Window w3, then w3 will remain null when the overloaded constructor is executed.

Here is the code from the book:

import static net.mindview.util.Print.*;
    // When the constructor is called to create a
    // Window object, you’ll see a message:
    class Window {
        Window(int marker) 
        { 
            print("Window(" + marker + ")"); 
        } 
    }

   class House { 
       Window w1 = new Window(1); 
       // Before constructor 
       House() {
           // Show that we’re in the constructor:
           print("House()");
           w3 = new Window(33); // Reinitialize w3
       }
        Window w2 = new Window(2); 
        // After constructor void f() { print("f()"); } 
        Window w3 = new Window(3); 
    // At end 
   }