//: appendixa:CopyConstructor.java // From 'Thinking in Java, 2nd ed.' by Bruce Eckel // www.BruceEckel.com. See copyright notice in CopyRight.txt. // A constructor for copying an object of the same // type, as an attempt to create a local copy. class FruitQualities { private int weight; private int color; private int firmness; private int ripeness; private int smell; // etc. FruitQualities() { // Default constructor // do something meaningful... } // Other constructors: // ... // Copy constructor: FruitQualities(FruitQualities f) { weight = f.weight; color = f.color; firmness = f.firmness; ripeness = f.ripeness; smell = f.smell; // etc. } } class Seed { // Members... Seed() { /* Default constructor */ } Seed(Seed s) { /* Copy constructor */ } } class Fruit { private FruitQualities fq; private int seeds; private Seed[] s; Fruit(FruitQualities q, int seedCount) { fq = q; seeds = seedCount; s = new Seed[seeds]; for(int i = 0; i < seeds; i++) s[i] = new Seed(); } // Other constructors: // ... // Copy constructor: Fruit(Fruit f) { fq = new FruitQualities(f.fq); seeds = f.seeds; // Call all Seed copy-constructors: for(int i = 0; i < seeds; i++) s[i] = new Seed(f.s[i]); // Other copy-construction activities... } // To allow derived constructors (or other // methods) to put in different qualities: protected void addQualities(FruitQualities q) { fq = q; } protected FruitQualities getQualities() { return fq; } } class Tomato extends Fruit { Tomato() { super(new FruitQualities(), 100); } Tomato(Tomato t) { // Copy-constructor super(t); // Upcast for base copy-constructor // Other copy-construction activities... } } class ZebraQualities extends FruitQualities { private int stripedness; ZebraQualities() { // Default constructor // do something meaningful... } ZebraQualities(ZebraQualities z) { super(z); stripedness = z.stripedness; } } class GreenZebra extends Tomato { GreenZebra() { addQualities(new ZebraQualities()); } GreenZebra(GreenZebra g) { super(g); // Calls Tomato(Tomato) // Restore the right qualities: addQualities(new ZebraQualities()); } void evaluate() { ZebraQualities zq = (ZebraQualities)getQualities(); // Do something with the qualities // ... } } public class CopyConstructor { public static void ripen(Tomato t) { // Use the "copy constructor": t = new Tomato(t); System.out.println("In ripen, t is a " + t.getClass().getName()); } public static void slice(Fruit f) { f = new Fruit(f); // Hmmm... will this work? System.out.println("In slice, f is a " + f.getClass().getName()); } public static void main(String[] args) { Tomato tomato = new Tomato(); ripen(tomato); // OK slice(tomato); // OOPS! GreenZebra g = new GreenZebra(); ripen(g); // OOPS! slice(g); // OOPS! g.evaluate(); } } ///:~