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в 18:01, 31 мая 2010

2010-05-31T18:01:44Z

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== A changeable wrapper class ==



<source lang="java">
// : appendixa:MutableInteger.java
// A changeable wrapper class.
// From "Thinking in Java, 3rd ed." (c) Bruce Eckel 2002
// www.BruceEckel.ru. See copyright notice in CopyRight.txt.
import java.util.ArrayList;
import java.util.List;
class IntValue {
private int n;
public IntValue(int x) {
n = x;
}
public int getValue() {
return n;
}
public void setValue(int n) {
this.n = n;
}
public void increment() {
n++;
}
public String toString() {
return Integer.toString(n);
}
}
public class MutableInteger {
public static void main(String[] args) {
List v = new ArrayList();
for (int i = 0; i < 10; i++)
v.add(new IntValue(i));
System.out.println(v);
for (int i = 0; i < v.size(); i++)
((IntValue) v.get(i)).increment();
System.out.println(v);
}
} ///:~

</source>



== A companion class to modify immutable objects ==



<source lang="java">
// : appendixa:Immutable2.java
// A companion class to modify immutable objects.
// From "Thinking in Java, 3rd ed." (c) Bruce Eckel 2002
// www.BruceEckel.ru. See copyright notice in CopyRight.txt.
class Mutable {
private int data;
public Mutable(int initVal) {
data = initVal;
}
public Mutable add(int x) {
data += x;
return this;
}
public Mutable multiply(int x) {
data *= x;
return this;
}
public Immutable2 makeImmutable2() {
return new Immutable2(data);
}
}
public class Immutable2 {
private int data;
public Immutable2(int initVal) {
data = initVal;
}
public int read() {
return data;
}
public boolean nonzero() {
return data != 0;
}
public Immutable2 add(int x) {
return new Immutable2(data + x);
}
public Immutable2 multiply(int x) {
return new Immutable2(data * x);
}
public Mutable makeMutable() {
return new Mutable(data);
}
public static Immutable2 modify1(Immutable2 y) {
Immutable2 val = y.add(12);
val = val.multiply(3);
val = val.add(11);
val = val.multiply(2);
return val;
}
// This produces the same result:
public static Immutable2 modify2(Immutable2 y) {
Mutable m = y.makeMutable();
m.add(12).multiply(3).add(11).multiply(2);
return m.makeImmutable2();
}
public static void main(String[] args) {
Immutable2 i2 = new Immutable2(47);
Immutable2 r1 = modify1(i2);
Immutable2 r2 = modify2(i2);
System.out.println("i2 = " + i2.read());
System.out.println("r1 = " + r1.read());
System.out.println("r2 = " + r2.read());
}
} ///:~

</source>



== Create Object Demo ==



<source lang="java">
/* From http://java.sun.ru/docs/books/tutorial/index.html */
/*
* Copyright (c) 2006 Sun Microsystems, Inc. All Rights Reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are met:
*
* -Redistribution of source code must retain the above copyright notice, this
* list of conditions and the following disclaimer.
*
* -Redistribution in binary form must reproduce the above copyright notice,
* this list of conditions and the following disclaimer in the documentation
* and/or other materials provided with the distribution.
*
* Neither the name of Sun Microsystems, Inc. or the names of contributors may
* be used to endorse or promote products derived from this software without
* specific prior written permission.
*
* This software is provided "AS IS," without a warranty of any kind. ALL
* EXPRESS OR IMPLIED CONDITIONS, REPRESENTATIONS AND WARRANTIES, INCLUDING
* ANY IMPLIED WARRANTY OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE
* OR NON-INFRINGEMENT, ARE HEREBY EXCLUDED. SUN MIDROSYSTEMS, INC. ("SUN")
* AND ITS LICENSORS SHALL NOT BE LIABLE FOR ANY DAMAGES SUFFERED BY LICENSEE
* AS A RESULT OF USING, MODIFYING OR DISTRIBUTING THIS SOFTWARE OR ITS
* DERIVATIVES. IN NO EVENT WILL SUN OR ITS LICENSORS BE LIABLE FOR ANY LOST
* REVENUE, PROFIT OR DATA, OR FOR DIRECT, INDIRECT, SPECIAL, CONSEQUENTIAL,
* INCIDENTAL OR PUNITIVE DAMAGES, HOWEVER CAUSED AND REGARDLESS OF THE THEORY
* OF LIABILITY, ARISING OUT OF THE USE OF OR INABILITY TO USE THIS SOFTWARE,
* EVEN IF SUN HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES.
*
* You acknowledge that this software is not designed, licensed or intended
* for use in the design, construction, operation or maintenance of any
* nuclear facility.
*/
public class CreateObjectDemo {
public static void main(String[] args) {
// create a point object and two rectangle objects
Point origin_one = new Point(23, 94);
Rectangle rect_one = new Rectangle(origin_one, 100, 200);
Rectangle rect_two = new Rectangle(50, 100);
// display rect_one"s width, height, and area
System.out.println("Width of rect_one: " + rect_one.width);
System.out.println("Height of rect_one: " + rect_one.height);
System.out.println("Area of rect_one: " + rect_one.area());
// set rect_two"s position
rect_two.origin = origin_one;
// display rect_two"s position
System.out.println("X Position of rect_two: " + rect_two.origin.x);
System.out.println("Y Position of rect_two: " + rect_two.origin.y);
// move rect_two and display its new position
rect_two.move(40, 72);
System.out.println("X Position of rect_two: " + rect_two.origin.x);
System.out.println("Y Position of rect_two: " + rect_two.origin.y);
}
}
class Point {
public int x = 0;
public int y = 0;
// a constructor!
public Point(int x, int y) {
this.x = x;
this.y = y;
}
}
class Rectangle {
public int width = 0;
public int height = 0;
public Point origin;
// four constructors
public Rectangle() {
origin = new Point(0, 0);
}
public Rectangle(Point p) {
origin = p;
}
public Rectangle(int w, int h) {
this(new Point(0, 0), w, h);
}
public Rectangle(Point p, int w, int h) {
origin = p;
width = w;
height = h;
}
// a method for moving the rectangle
public void move(int x, int y) {
origin.x = x;
origin.y = y;
}
// a method for computing the area of the rectangle
public int area() {
return width * height;
}
}

</source>



== Demonstrates Reference objects ==



<source lang="java">
// : c11:References.java
// Demonstrates Reference objects
// From "Thinking in Java, 3rd ed." (c) Bruce Eckel 2002
// www.BruceEckel.ru. See copyright notice in CopyRight.txt.
import java.lang.ref.PhantomReference;
import java.lang.ref.Reference;
import java.lang.ref.ReferenceQueue;
import java.lang.ref.SoftReference;
import java.lang.ref.WeakReference;
class VeryBig {
private static final int SZ = 10000;
private double[] d = new double[SZ];
private String ident;
public VeryBig(String id) {
ident = id;
}
public String toString() {
return ident;
}
public void finalize() {
System.out.println("Finalizing " + ident);
}
}
public class References {
private static ReferenceQueue rq = new ReferenceQueue();
public static void checkQueue() {
Object inq = rq.poll();
if (inq != null)
System.out
.println("In queue: " + (VeryBig) ((Reference) inq).get());
}
public static void main(String[] args) {
int size = 10;
// Or, choose size via the command line:
if (args.length > 0)
size = Integer.parseInt(args[0]);
SoftReference[] sa = new SoftReference[size];
for (int i = 0; i < sa.length; i++) {
sa[i] = new SoftReference(new VeryBig("Soft " + i), rq);
System.out.println("Just created: " + (VeryBig) sa[i].get());
checkQueue();
}
WeakReference[] wa = new WeakReference[size];
for (int i = 0; i < wa.length; i++) {
wa[i] = new WeakReference(new VeryBig("Weak " + i), rq);
System.out.println("Just created: " + (VeryBig) wa[i].get());
checkQueue();
}
SoftReference s = new SoftReference(new VeryBig("Soft"));
WeakReference w = new WeakReference(new VeryBig("Weak"));
System.gc();
PhantomReference[] pa = new PhantomReference[size];
for (int i = 0; i < pa.length; i++) {
pa[i] = new PhantomReference(new VeryBig("Phantom " + i), rq);
System.out.println("Just created: " + (VeryBig) pa[i].get());
checkQueue();
}
}
} ///:~

</source>



== Examination of the way the class loader works ==



<source lang="java">
// : c10:SweetShop.java
// Examination of the way the class loader works.
// From "Thinking in Java, 3rd ed." (c) Bruce Eckel 2002
// www.BruceEckel.ru. See copyright notice in CopyRight.txt.
class Candy {
static {
System.out.println("Loading Candy");
}
}
class Gum {
static {
System.out.println("Loading Gum");
}
}
class Cookie {
static {
System.out.println("Loading Cookie");
}
}
public class SweetShop {
public static void main(String[] args) {
System.out.println("inside main");
new Candy();
System.out.println("After creating Candy");
try {
Class.forName("Gum");
} catch (ClassNotFoundException e) {
System.out.println("Couldn"t find Gum");
}
System.out.println("After Class.forName(\"Gum\")");
new Cookie();
System.out.println("After creating Cookie");
}
} ///:~

</source>



== Objects that cannot be modified are immune to aliasing ==



<source lang="java">

// : appendixa:Immutable1.java
// Objects that cannot be modified are immune to aliasing.
// From "Thinking in Java, 3rd ed." (c) Bruce Eckel 2002
// www.BruceEckel.ru. See copyright notice in CopyRight.txt.
public class Immutable1 {
private int data;
public Immutable1(int initVal) {
data = initVal;
}
public int read() {
return data;
}
public boolean nonzero() {
return data != 0;
}
public Immutable1 multiply(int multiplier) {
return new Immutable1(data * multiplier);
}
public static void f(Immutable1 i1) {
Immutable1 quad = i1.multiply(4);
System.out.println("i1 = " + i1.read());
System.out.println("quad = " + quad.read());
}
public static void main(String[] args) {
Immutable1 x = new Immutable1(47);
System.out.println("x = " + x.read());
f(x);
System.out.println("x = " + x.read());
}
} ///:~

</source>



== Passing objects to methods may not be what you"re used to. ==



<source lang="java">
//: c03:PassObject.java
// From "Thinking in Java, 3rd ed." (c) Bruce Eckel 2002
// www.BruceEckel.ru. See copyright notice in CopyRight.txt.
class Letter {
char c;
}
public class PassObject {
static void f(Letter y) {
y.c = "z";
}
public static void main(String[] args) {
Letter x = new Letter();
x.c = "a";
System.out.println("1: x.c: " + x.c);
f(x);
System.out.println("2: x.c: " + x.c);
}
} ///:~

</source>

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Admin: 1 версия

в 18:01, 31 мая 2010