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== Array reflection and two dimensional array ==



<source lang="java">
/*
* Copyright (c) 1995 - 2008 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:
*
* - Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
*
* - Redistributions 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 nor the names of its
* contributors may be used to endorse or promote products derived
* from this software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
* IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
* THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
* PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
* CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
* EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
* PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
* PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
* LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
* NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
* SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
import static java.lang.System.out;
import java.lang.reflect.Array;
public class CreateMatrix {
public static void main(String... args) {
Object matrix = Array.newInstance(int.class, 2, 2);
Object row0 = Array.get(matrix, 0);
Object row1 = Array.get(matrix, 1);
Array.setInt(row0, 0, 1);
Array.setInt(row0, 1, 2);
Array.setInt(row1, 0, 3);
Array.setInt(row1, 1, 4);
for (int i = 0; i < 2; i++)
for (int j = 0; j < 2; j++)
out.format("matrix[%d][%d] = %d%n", i, j, ((int[][]) matrix)[i][j]);
}
}</source>



== class name for double and float array ==



<source lang="java">
class ClassInfoDemo2 {
public static void main(String[] args) {
Class c = String.class;
System.out.println(c.getName());
c = ClassInfoDemo2.class;
System.out.println(c.getName());
c = double.class;
System.out.println(c.getName());
c = float[].class;
System.out.println(c.getName());
}
}</source>



== Create array with Array.newInstance ==



<source lang="java">
/*
* Copyright (c) 1995 - 2008 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:
*
* - Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
*
* - Redistributions 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 nor the names of its
* contributors may be used to endorse or promote products derived
* from this software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
* IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
* THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
* PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
* CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
* EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
* PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
* PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
* LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
* NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
* SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
import static java.lang.System.out;
import java.lang.reflect.Array;
import java.lang.reflect.Constructor;
import java.lang.reflect.InvocationTargetException;
import java.util.Arrays;
import java.util.regex.Matcher;
import java.util.regex.Pattern;
public class ArrayCreator {
private static String s = "java.math.BigInteger bi[] = { 123, 234, 345 }";
private static Pattern p = Pattern
.rupile("^\\s*(\\S+)\\s*\\w+\\[\\].*\\{\\s*([^}]+)\\s*\\}");
public static void main(String... args) {
Matcher m = p.matcher(s);
if (m.find()) {
String cName = m.group(1);
String[] cVals = m.group(2).split("[\\s,]+");
int n = cVals.length;
try {
Class<?> c = Class.forName(cName);
Object o = Array.newInstance(c, n);
for (int i = 0; i < n; i++) {
String v = cVals[i];
Constructor ctor = c.getConstructor(String.class);
Object val = ctor.newInstance(v);
Array.set(o, i, val);
}
Object[] oo = (Object[]) o;
out.format("%s[] = %s%n", cName, Arrays.toString(oo));
// production code should handle these exceptions more gracefully
} catch (ClassNotFoundException x) {
x.printStackTrace();
} catch (NoSuchMethodException x) {
x.printStackTrace();
} catch (IllegalAccessException x) {
x.printStackTrace();
} catch (InstantiationException x) {
x.printStackTrace();
} catch (InvocationTargetException x) {
x.printStackTrace();
}
}
}
}</source>



== Create integer array with Array.newInstance ==



<source lang="java">
/*
* Copyright (c) 1995 - 2008 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:
*
* - Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
*
* - Redistributions 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 nor the names of its
* contributors may be used to endorse or promote products derived
* from this software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
* IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
* THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
* PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
* CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
* EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
* PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
* PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
* LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
* NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
* SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
import static java.lang.System.out;
import java.lang.reflect.Array;
public class ArrayTrouble {
public static void main(String... args) {
Object o = Array.newInstance(int.class, 0);
int[] i = (int[]) o;
int[] j = new int[0];
out.format("i.length = %d, j.length = %d, args.length = %d%n", i.length,
j.length, args.length);
Array.getInt(o, 0); // ArrayIndexOutOfBoundsException
}
}</source>



== Demonstrates the use of the Array class ==



<source lang="java">
/*
* file: ArrayDemo.java
* package: oreilly.hcj.reflection
*
* This software is granted under the terms of the Common Public License,
* CPL, which may be found at the following URL:
* http://www-124.ibm.ru/developerworks/oss/CPLv1.0.htm
*
* Copyright(c) 2003-2005 by the authors indicated in the @author tags.
* All Rights are Reserved by the various authors.
*
########## DO NOT EDIT ABOVE THIS LINE ########## */

import java.lang.reflect.Array;
/**
* Demonstrates the use of the Array class.
*
* @author
* @version $Revision$
*/
public class ArrayDemo {
/**
* Copy an array and return the copy.
*
* @param input The array to copy.
*
* @return The coppied array.
*
* @throws IllegalArgumentException If input is not an array.
*/
public static Object copyArray(final Object input) {
final Class type = input.getClass();
if (!type.isArray()) {
throw new IllegalArgumentException();
}
final int length = Array.getLength(input);
final Class componentType = type.getComponentType();
final Object result = Array.newInstance(componentType, length);
for (int idx = 0; idx < length; idx++) {
Array.set(result, idx, Array.get(input, idx));
}
return result;
}
/**
* Run the demo.
*
* @param args Command line arguments (ignored).
*/
public static void main(final String[] args) {
try {
int[] x = new int[] { 2, 3, 8, 7, 5 };
char[] y = new char[] { "a", "z", "e" };
String[] z = new String[] { "Jim", "John", "Joe" };
System.out.println(" -- x and y --");
outputArrays(x, y);
System.out.println(" -- x and copy of x --");
outputArrays(x, copyArray(x));
System.out.println(" -- y and copy of y --");
outputArrays(y, copyArray(y));
System.out.println(" -- z and copy of z --");
outputArrays(z, copyArray(z));
} catch (final Exception ex) {
ex.printStackTrace();
}
}
/**
* Print out 2 arrays in columnar format.
*
* @param first The array for the first column.
* @param second The array for the second column.
*
* @throws IllegalArgumentException __UNDOCUMENTED__
*/
public static void outputArrays(final Object first, final Object second) {
if (!first.getClass()
.isArray()) {
throw new IllegalArgumentException("first is not an array.");
}
if (!second.getClass()
.isArray()) {
throw new IllegalArgumentException("second is not an array.");
}
final int lengthFirst = Array.getLength(first);
final int lengthSecond = Array.getLength(second);
final int length = Math.max(lengthFirst, lengthSecond);
for (int idx = 0; idx < length; idx++) {
System.out.print("[" + idx + "]\t");
if (idx < lengthFirst) {
System.out.print(Array.get(first, idx) + "\t\t");
} else {
System.out.print("\t\t");
}
if (idx < lengthSecond) {
System.out.print(Array.get(second, idx) + "\t");
}
System.out.println();
}
}
}
/* ########## End of File ########## */</source>



== Determining If an Object Is an Array ==



<source lang="java">
public class Main {
public static void main(String[] argv) throws Exception {
boolean b = "".getClass().isArray();
if (b) {
System.out.println("object is an array");
}
}
}</source>



== Getting the Component Type of an Array Object ==



<source lang="java">
public class Main {
public static void main(String[] argv) throws Exception {
Object o = new int[1][2][3];
o.getClass().getComponentType();
}
}</source>



== Getting the Length and Dimensions of an Array Object ==



<source lang="java">
import java.lang.reflect.Array;
public class Main {
public static void main(String[] argv) throws Exception {
Object o = new int[1][2][3];
int len = Array.getLength(o); // 1
System.out.println(len);
int dim = getDim(o); // 3
System.out.println(dim);
}
public static int getDim(Object array) {
int dim = 0;
Class cls = array.getClass();
while (cls.isArray()) {
dim++;
cls = cls.getComponentType();
}
return dim;
}
}</source>



== Is field an array ==



<source lang="java">
/*
* Copyright (c) 1995 - 2008 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:
*
* - Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
*
* - Redistributions 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 nor the names of its
* contributors may be used to endorse or promote products derived
* from this software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
* IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
* THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
* PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
* CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
* EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
* PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
* PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
* LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
* NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
* SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
import static java.lang.System.out;
import java.lang.reflect.Field;
public class ArrayFind {
public static void main(String... args) {
boolean found = false;
try {
Class<?> cls = Class.forName(args[0]);
Field[] flds = cls.getDeclaredFields();
for (Field f : flds) {
Class<?> c = f.getType();
if (c.isArray()) {
found = true;
out.format("%s%n" + " Field: %s%n"
+ " Type: %s%n" + " Component Type: %s%n", f, f
.getName(), c, c.getComponentType());
}
}
if (!found) {
out.format("No array fields%n");
}
// production code should handle this exception more gracefully
} catch (ClassNotFoundException x) {
x.printStackTrace();
}
}
}</source>



== Returns the length of the specified array, can deal with Object arrays and with primitive arrays. ==



<source lang="java">
/* Copyright 2004 The Apache Software Foundation
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/

import java.lang.reflect.Array;

/**
* Operations on arrays, primitive arrays (like <code>int[]</code>) and
* primitive wrapper arrays (like <code>Integer[]</code>).
*
* This class tries to handle <code>null</code> input gracefully.
* An exception will not be thrown for a <code>null</code>
* array input. However, an Object array that contains a <code>null</code>
* element may throw an exception. Each method documents its behaviour.
*
* @author Stephen Colebourne
* @author Moritz Petersen
* @author
* @author Maarten Coene
* @since 2.0
* @version $Id: ArrayUtils.java 632503 2008-03-01 00:21:52Z ggregory $
*/
public class Main {
//-----------------------------------------------------------------------
/**
* Returns the length of the specified array.
* This method can deal with <code>Object</code> arrays and with primitive arrays.
*
* If the input array is <code>null</code>, <code>0</code> is returned.
*
* <pre>
* ArrayUtils.getLength(null) = 0
* ArrayUtils.getLength([]) = 0
* ArrayUtils.getLength([null]) = 1
* ArrayUtils.getLength([true, false]) = 2
* ArrayUtils.getLength([1, 2, 3]) = 3
* ArrayUtils.getLength(["a", "b", "c"]) = 3
* </pre>
*
* @param array the array to retrieve the length from, may be null
* @return The length of the array, or <code>0</code> if the array is <code>null</code>
* @throws IllegalArgumentException if the object arguement is not an array.
* @since 2.1
*/
public static int getLength(Object array) {
if (array == null) {
return 0;
}
return Array.getLength(array);
}
}</source>



== Use Array.setInt to fill an array ==



<source lang="java">
/*
* Copyright (c) 1995 - 2008 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:
*
* - Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
*
* - Redistributions 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 nor the names of its
* contributors may be used to endorse or promote products derived
* from this software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
* IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
* THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
* PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
* CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
* EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
* PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
* PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
* LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
* NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
* SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
import static java.lang.System.err;
import java.lang.reflect.Array;
public class ArrayTroubleAgain {
public static void main(String... args) {
Integer[] ary = new Integer[2];
try {
Array.setInt(ary, 0, 1); // IllegalArgumentException
// production code should handle these exceptions more gracefully
} catch (IllegalArgumentException x) {
err.format("Unable to box%n");
} catch (ArrayIndexOutOfBoundsException x) {
x.printStackTrace();
}
}
}</source>



== Use Array.setShort and Array.setLong ==



<source lang="java">
/*
* Copyright (c) 1995 - 2008 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:
*
* - Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
*
* - Redistributions 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 nor the names of its
* contributors may be used to endorse or promote products derived
* from this software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
* IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
* THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
* PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
* CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
* EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
* PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
* PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
* LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
* NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
* SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
import java.lang.reflect.Array;
public class ArrayTroubleToo {
public static void main(String... args) {
Object o = new int[2];
Array.setShort(o, 0, (short) 2); // widening, succeeds
Array.setLong(o, 1, 2L); // narrowing, fails
}
}</source>

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