Java:thinking in java p241 exercise1

標籤：

Create a simple class. Inside a second class, define a reference to an object of the first class. Use lazy initialization to instantiate this object.

 1 import static org.greggordon.tools.Print.*; 2  3 class Engine { 4     private String s; 5     Engine() { 6         println("Engine()"); 7         s = "Constructed"; 8     } 9     public String toString() { return s; }10 }11 12 public class Airplane {13     private String fuselage, wings, tail;14     private Engine e;15     public Airplane() {16         println("Inside Airplane()");17         fuselage = "Body";18         wings = "Airfoils";19         tail = "Empennage";                20     }21     public String toString() { 22         if(e == null) // lazy (delayed) initialization:23             e = new Engine();24         return "fuselage = " + fuselage + ", " +25             "wings = " + wings + ", " +26             "tail = " + tail + ", " +27             "Engine = " + e;28     }29     public static void main(String[] args) {30         Airplane N1234 = new Airplane();31         print(N1234);32     }33 }

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Java:thinking in java p241 exercise1