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2010-06-01T07:27:26Z

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в 18:01, 31 мая 2010

2010-05-31T18:01:50Z

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== Bounded Wildcard arguments. ==



<source lang="java">

class TwoD {
int x, y;
TwoD(int a, int b) {
x = a;
y = b;
}
}
class ThreeD extends TwoD {
int z;
ThreeD(int a, int b, int c) {
super(a, b);
z = c;
}
}
class FourD extends ThreeD {
int t;
FourD(int a, int b, int c, int d) {
super(a, b, c);
t = d;
}
}
class Coords<T extends TwoD> {
T[] coords;
Coords(T[] o) {
coords = o;
}
}
class BoundedWildcard {
static void showXY(Coords<?> c) {
System.out.println("X Y Coordinates:");
for (int i = 0; i < c.coords.length; i++)
System.out.println(c.coords[i].x + " " + c.coords[i].y);
System.out.println();
}
static void showXYZ(Coords<? extends ThreeD> c) {
System.out.println("X Y Z Coordinates:");
for (int i = 0; i < c.coords.length; i++)
System.out.println(c.coords[i].x + " " + c.coords[i].y + " " + c.coords[i].z);
System.out.println();
}
static void showAll(Coords<? extends FourD> c) {
System.out.println("X Y Z T Coordinates:");
for (int i = 0; i < c.coords.length; i++)
System.out.println(c.coords[i].x + " " + c.coords[i].y + " " + c.coords[i].z + " "
+ c.coords[i].t);
System.out.println();
}
public static void main(String args[]) {
TwoD td[] = { new TwoD(0, 0), new TwoD(7, 9), new TwoD(18, 4), new TwoD(-1, -23) };
Coords<TwoD> tdlocs = new Coords<TwoD>(td);
System.out.println("Contents of tdlocs.");
showXY(tdlocs); // OK, is a TwoD
FourD fd[] = { new FourD(1, 2, 3, 4), new FourD(6, 8, 14, 8), new FourD(22, 9, 4, 9),
new FourD(3, -2, -23, 17) };
Coords<FourD> fdlocs = new Coords<FourD>(fd);
System.out.println("Contents of fdlocs.");
// These are all OK.
showXY(fdlocs);
showXYZ(fdlocs);
showAll(fdlocs);
}
}

</source>



== Generic cast ==



<source lang="java">

/*
* Copyright (C) 2001-2003 Colin Bell
* colbell@users.sourceforge.net
*
* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation; either
* version 2.1 of the License, or (at your option) any later version.
*
* This library is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with this library; if not, write to the Free Software
* Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
*/
import java.io.*;
import java.text.NumberFormat;
import java.util.regex.Matcher;
import java.util.regex.Pattern;
/**
* General purpose utilities functions.
*
* @author
*/
public class Utilities
{

/**
* This is taken from Eammon McManus" blog:
* http://weblogs.java.net/blog/emcmanus/archive/2007/03/getting_rid_of.html This prevents you from having
* to place SuppressWarnings throughout your code.
*
* @param <T>
* the return type to cast the object to
* @param x
* the object to cast.
* @return a type-casted version of the specified object.
*/
@SuppressWarnings("unchecked")
public static <T> T cast(Object x) {
return (T) x;
}
}

</source>



== Java generic: Bounded Wildcard arguments ==



<source lang="java">

/*
Java 2, v5.0 (Tiger) New Features
by Herbert Schildt
ISBN: 0072258543
Publisher: McGraw-Hill/Osborne, 2004
*/

// Two-dimensional coordinates.
class TwoD {
int x, y;

TwoD(int a, int b) {
x = a;
y = b;
}
}

// Three-dimensional coordinates.
class ThreeD extends TwoD {
int z;

ThreeD(int a, int b, int c) {
super(a, b);
z = c;
}
}

// Four-dimensional coordinates.
class FourD extends ThreeD {
int t;

FourD(int a, int b, int c, int d) {
super(a, b, c);
t = d;
}
}

// This class holds an array of coordinate objects.
class Coords<T extends TwoD> {
T[] coords;

Coords(T[] o) { coords = o; }
}

// Demonstrate a bounded wildcard.
public class BoundedWildcard {
static void showXY(Coords<?> c) {
System.out.println("X Y Coordinates:");
for(int i=0; i < c.coords.length; i++)
System.out.println(c.coords[i].x + " " +
c.coords[i].y);
System.out.println();
}

static void showXYZ(Coords<? extends ThreeD> c) {
System.out.println("X Y Z Coordinates:");
for(int i=0; i < c.coords.length; i++)
System.out.println(c.coords[i].x + " " +
c.coords[i].y + " " +
c.coords[i].z);
System.out.println();
}

static void showAll(Coords<? extends FourD> c) {
System.out.println("X Y Z T Coordinates:");
for(int i=0; i < c.coords.length; i++)
System.out.println(c.coords[i].x + " " +
c.coords[i].y + " " +
c.coords[i].z + " " +
c.coords[i].t);
System.out.println();
}

public static void main(String args[]) {
TwoD td[] = {
new TwoD(0, 0),
new TwoD(7, 9),
new TwoD(18, 4),
new TwoD(-1, -23)
};

Coords<TwoD> tdlocs = new Coords<TwoD>(td);

System.out.println("Contents of tdlocs.");
showXY(tdlocs); // OK, is a TwoD
// showXYZ(tdlocs); // Error, not a ThreeD
// showAll(tdlocs); // Erorr, not a FourD

// Now, create some FourD objects.
FourD fd[] = {
new FourD(1, 2, 3, 4),
new FourD(6, 8, 14, 8),
new FourD(22, 9, 4, 9),
new FourD(3, -2, -23, 17)
};

Coords<FourD> fdlocs = new Coords<FourD>(fd);

System.out.println("Contents of fdlocs.");
// These are all OK.
showXY(fdlocs);
showXYZ(fdlocs);
showAll(fdlocs);
}
}

</source>



== Java generic: Use a wildcard. ==



<source lang="java">

/*
Java 2, v5.0 (Tiger) New Features
by Herbert Schildt
ISBN: 0072258543
Publisher: McGraw-Hill/Osborne, 2004
*/

class Stats<T extends Number> {
T[] nums; // array of Number or subclass

// Pass the constructor a reference to
// an array of type Number or subclass.
Stats(T[] o) {
nums = o;
}

// Return type double in all cases.
double average() {
double sum = 0.0;

for(int i=0; i < nums.length; i++)
sum += nums[i].doubleValue();

return sum / nums.length;
}

// Determine if two averages are the same.
// Notice the use of the wildcard.
boolean sameAvg(Stats<?> ob) {
if(average() == ob.average())
return true;

return false;
}
}

// Demonstrate wildcard.
public class WildcardDemo {
public static void main(String args[]) {
Integer inums[] = { 1, 2, 3, 4, 5 };
Stats<Integer> iob = new Stats<Integer>(inums);
double v = iob.average();
System.out.println("iob average is " + v);

Double dnums[] = { 1.1, 2.2, 3.3, 4.4, 5.5 };
Stats<Double> dob = new Stats<Double>(dnums);
double w = dob.average();
System.out.println("dob average is " + w);

Float fnums[] = { 1.0F, 2.0F, 3.0F, 4.0F, 5.0F };
Stats<Float> fob = new Stats<Float>(fnums);
double x = fob.average();
System.out.println("fob average is " + x);

// See which arrays have same average.
System.out.print("Averages of iob and dob ");
if(iob.sameAvg(dob))
System.out.println("are the same.");
else
System.out.println("differ.");

System.out.print("Averages of iob and fob ");
if(iob.sameAvg(fob))
System.out.println("are the same.");
else
System.out.println("differ.");
}
}

</source>



== Use a wildcard. ==



<source lang="java">

class Stats<T extends Number> {
T[] nums;
Stats(T[] o) {
nums = o;
}
double average() {
double sum = 0.0;
for (int i = 0; i < nums.length; i++)
sum += nums[i].doubleValue();
return sum / nums.length;
}
boolean sameAvg(Stats<?> ob) {
if (average() == ob.average())
return true;
return false;
}
}
class WildcardDemo {
public static void main(String args[]) {
Integer inums[] = { 1, 2, 3, 4, 5 };
Stats<Integer> iob = new Stats<Integer>(inums);
double v = iob.average();
System.out.println("iob average is " + v);
Double dnums[] = { 1.1, 2.2, 3.3, 4.4, 5.5 };
Stats<Double> dob = new Stats<Double>(dnums);
double w = dob.average();
System.out.println("dob average is " + w);
Float fnums[] = { 1.0F, 2.0F, 3.0F, 4.0F, 5.0F };
Stats<Float> fob = new Stats<Float>(fnums);
double x = fob.average();
System.out.println("fob average is " + x);
// See which arrays have same average.
System.out.print("Averages of iob and dob ");
if (iob.sameAvg(dob))
System.out.println("are the same.");
else
System.out.println("differ.");
System.out.print("Averages of iob and fob ");
if (iob.sameAvg(fob))
System.out.println("are the same.");
else
System.out.println("differ.");
}
}

</source>

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Admin: 1 версия

в 18:01, 31 мая 2010