Mega Code Archive
A constructor for copying an object of the same
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// : appendixa:CopyConstructor.java
// A constructor for copying an object of the same
// type, as an attempt to create a local copy.
// From 'Thinking in Java, 3rd ed.' (c) Bruce Eckel 2002
// www.BruceEckel.com. See copyright notice in CopyRight.txt.
import java.lang.reflect.Constructor;
class FruitQualities {
private int weight;
private int color;
private int firmness;
private int ripeness;
private int smell;
// etc.
public FruitQualities() { // Default constructor
// Do something meaningful...
}
// Other constructors:
// ...
// Copy constructor:
public FruitQualities(FruitQualities f) {
weight = f.weight;
color = f.color;
firmness = f.firmness;
ripeness = f.ripeness;
smell = f.smell;
// etc.
}
}
class Seed {
// Members...
public Seed() { /* Default constructor */
}
public Seed(Seed s) { /* Copy constructor */
}
}
class Fruit {
private FruitQualities fq;
private int seeds;
private Seed[] s;
public 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:
public Fruit(Fruit f) {
fq = new FruitQualities(f.fq);
seeds = f.seeds;
s = new Seed[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 {
public Tomato() {
super(new FruitQualities(), 100);
}
public Tomato(Tomato t) { // Copy-constructor
super(t); // Upcast for base copy-constructor
// Other copy-construction activities...
}
}
class ZebraQualities extends FruitQualities {
private int stripedness;
public ZebraQualities() { // Default constructor
super();
// do something meaningful...
}
public ZebraQualities(ZebraQualities z) {
super(z);
stripedness = z.stripedness;
}
}
class GreenZebra extends Tomato {
public GreenZebra() {
addQualities(new ZebraQualities());
}
public GreenZebra(GreenZebra g) {
super(g); // Calls Tomato(Tomato)
// Restore the right qualities:
addQualities(new ZebraQualities());
}
public 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 ripen2(Tomato t) {
try {
Class c = t.getClass();
// Use the "copy constructor":
Constructor ct = c.getConstructor(new Class[] { c });
Object obj = ct.newInstance(new Object[] { t });
System.out.println("In ripen2, t is a " + obj.getClass().getName());
} catch (Exception e) {
System.out.println(e);
}
}
public static void slice2(Fruit f) {
try {
Class c = f.getClass();
Constructor ct = c.getConstructor(new Class[] { c });
Object obj = ct.newInstance(new Object[] { f });
System.out.println("In slice2, f is a " + obj.getClass().getName());
} catch (Exception e) {
System.out.println(e);
}
}
public static void main(String[] args) {
Tomato tomato = new Tomato();
ripen(tomato); // OK
slice(tomato); // OOPS!
ripen2(tomato); // OK
slice2(tomato); // OK
GreenZebra g = new GreenZebra();
ripen(g); // OOPS!
slice(g); // OOPS!
ripen2(g); // OK
slice2(g); // OK
g.evaluate();
}
} ///:~
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