| Utilities.java |
/*
* GeoTools - The Open Source Java GIS Toolkit
* http://geotools.org
*
* (C) 2001-2008, Open Source Geospatial Foundation (OSGeo)
*
* 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;
* version 2.1 of the License.
*
* 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.
*/
package org.geotools.util;
import java.io.ObjectStreamException;
import java.io.Serializable;
import java.util.AbstractQueue;
import java.util.Arrays;
import java.util.Collections;
import java.util.Iterator;
import java.util.Queue;
import java.util.Set;
import org.geotools.factory.Hints;
import org.geotools.resources.i18n.ErrorKeys;
import org.geotools.resources.i18n.Errors;
/**
* Miscellaneous methods, including cnvenience methods for {@link Object#equals equals} and
* {@link Object#hashCode hashCode} implementations. Example use case in a class called
* {@code Car}:
*
* <pre>
* public boolean equals(Object other) {
* if (this == aThat) {
* return true;
* }
* if (other == null || !other.getClass().equals(getClass())) {
* return false;
* }
* Car that = (Car) other;
* return Utilities.equals(this.name, that.name) &&
* Utilities.equals(this.numDoors, that.numDoors) &&
* Utilities.equals(this.gasMileage, that.gasMileage) &&
* Utilities.equals(this.color, that.color) &&
* Arrays .equals(this.maintenanceChecks, that.maintenanceChecks);
* }
* </pre>
*
* Note the usage of {@link Arrays} method for comparing arrays.
* <p>
* This class also provides convenience methods for computing {@linkplain Object#hashCode hash code}
* values. All those methods expect a {@code seed} argument, which is the hash code value computed
* for previous fields in a class. For the initial seed (the one for the field for which to compute
* an hash code), an arbitrary value must be provided. We suggest a different number for different
* class in order to reduce the risk of collision between "empty" instances of different classes.
* {@linkplain java.io.Serializable} classes can use {@code (int) serialVersionUID} for example.
*
* @since 2.5
* @source $URL: http://svn.osgeo.org/geotools/tags/2.7-M3/modules/library/metadata/src/main/java/org/geotools/util/Utilities.java $
* @version $Id: Utilities.java 35335 2010-05-03 14:39:15Z danieleromagnoli $
* @author Martin Desruisseaux (IRD)
*/
public final class Utilities {
/**
* An array of strings containing only white spaces. Strings' lengths are equal to their
* index in the {@code spaces} array. For example, {@code spaces[4]}œcontains a string of
* length 4. Strings are constructed only when first needed.
*/
private static final String[] spaces = new String[21];
static {
final int last = spaces.length - 1;
final char[] blancs = new char[last];
Arrays.fill(blancs, ' ');
spaces[last] = new String(blancs).intern();
}
/**
* A prime number used for hash code computation.
*/
private static final int PRIME_NUMBER = 37;
/**
* The singleton instance to be returned by {@link #emptyQueue}.
*/
private static final Queue<?> EMPTY_QUEUE = new EmptyQueue<Object>();
/**
* The class for the {@link #EMPTY_QUEUE} instance. Defined as a named class rather than
* anonymous in order to avoid serialization issue.
*/
private static final class EmptyQueue<E> extends AbstractQueue<E> implements Serializable {
/** For cross-version compatibility. **/
private static final long serialVersionUID = -6147951199761870325L;
/** No effect on an queue which is already empty. */
@Override
public void clear() {
}
/** Returns {@code true} is all case. */
@Override
public boolean isEmpty() {
return true;
}
/** Returns the size, which is always 0. */
public int size() {
return 0;
}
/** Returns an empty iterator. */
public Iterator<E> iterator() {
final Set<E> empty = Collections.emptySet();
return empty.iterator();
}
/** Always returns {@code false} since this queue doesn't accept any element. */
public boolean offer(E e) {
return false;
}
/** Always returns {@code null} since this queue is always empty. */
public E poll() {
return null;
}
/** Always returns {@code null} since this queue is always empty. */
public E peek() {
return null;
}
/** Returns the singleton instance of deserialization. */
protected Object readResolve() throws ObjectStreamException {
return EMPTY_QUEUE;
}
}
/**
* Forbid object creation.
*/
private Utilities() {
}
/**
* Returns {@code true} if the given booleans are equals. This overloaded flavor is provided
* only for allowing developper to invoke {@code equals} methods without consideration for
* the argument type.
*
* @param o1 The first value to compare.
* @param o2 The second value to compare.
* @return {@code true} if both values are equal.
*
* @see Boolean#equals
*/
public static boolean equals(boolean o1, boolean o2) {
return o1 == o2;
}
/**
* Returns {@code true} if the given characters are equals. This overloaded flavor is provided
* only for allowing developper to invoke {@code equals} methods without consideration for
* the argument type.
*
* @param o1 The first value to compare.
* @param o2 The second value to compare.
* @return {@code true} if both values are equal.
*
* @see Character#equals
*/
public static boolean equals(char o1, char o2) {
return o1 == o2;
}
/**
* Returns {@code true} if the given bytes are equals. This overloaded flavor is provided
* only for allowing developper to invoke {@code equals} methods without consideration for
* the argument type.
*
* @param o1 The first value to compare.
* @param o2 The second value to compare.
* @return {@code true} if both values are equal.
*
* @see Byte#equals
*/
public static boolean equals(byte o1, byte o2) {
return o1 == o2;
}
/**
* Returns {@code true} if the given shorts are equals. This overloaded flavor is provided
* only for allowing developper to invoke {@code equals} methods without consideration for
* the argument type.
*
* @param o1 The first value to compare.
* @param o2 The second value to compare.
* @return {@code true} if both values are equal.
*
* @see Short#equals
*/
public static boolean equals(short o1, short o2) {
return o1 == o2;
}
/**
* Returns {@code true} if the given integers are equals. This overloaded flavor is provided
* only for allowing developper to invoke {@code equals} methods without consideration for
* the argument type.
*
* @param o1 The first value to compare.
* @param o2 The second value to compare.
* @return {@code true} if both values are equal.
*
* @see Integer#equals
*/
public static boolean equals(int o1, int o2) {
return o1 == o2;
}
/**
* Returns {@code true} if the given longs are equals. This overloaded flavor is provided
* only for allowing developper to invoke {@code equals} methods without consideration for
* the argument type.
*
* @param o1 The first value to compare.
* @param o2 The second value to compare.
* @return {@code true} if both values are equal.
*
* @see Long#equals
*/
public static boolean equals(long o1, long o2) {
return o1 == o2;
}
/**
* Returns {@code true} if the given floats are equals. Positive and negative zero are
* considered different, while a NaN value is considered equal to other NaN values.
*
* @param o1 The first value to compare.
* @param o2 The second value to compare.
* @return {@code true} if both values are equal.
*
* @see Float#equals
*/
public static boolean equals(float o1, float o2) {
if (Float.floatToIntBits(o1) == Float.floatToIntBits(o2))
return true;
double tol = getTolerance();
final double min = o1 - o1 * tol;
final double max = o1 + o1 * tol;
return min <= o2 && o2 <= max;
}
/**
* Returns {@code true} if the given doubles are equals. Positive and negative zero are
* considered different, while a NaN value is considered equal to other NaN values.
*
* @param o1 The first value to compare.
* @param o2 The second value to compare.
* @return {@code true} if both values are equal.
*
* @see Double#equals
*/
public static boolean equals(double o1, double o2) {
if (Double.doubleToLongBits(o1) == Double.doubleToLongBits(o2))
return true;
double tol = getTolerance();
final double min = o1 - Math.signum(o1) * o1 * tol;
final double max = o1 + Math.signum(o1) * o1 * tol;
return min <= o2 && o2 <= max;
}
/**
* Gathers the tolerance for floating point comparisons
* @return The tolerance set in the hints, or its default value if not set
*/
private static double getTolerance() {
Double tol = ((Double) Hints.getSystemDefault(Hints.COMPARISON_TOLERANCE));
if(tol == null)
return Hints.COMPARISON_TOLERANCE.getDefault();
else
return tol;
}
/**
* Convenience method for testing two objects for equality. One or both objects may be null.
* This method do <strong>not</strong> iterates recursively in array elements. If array needs
* to be compared, use one of {@link Arrays} method or {@link #deepEquals deepEquals} instead.
* <p>
* <b>Note on assertions:</b> There is no way to ensure at compile time that this method
* is not invoked with array arguments, while doing so would usually be a program error.
* Performing a systematic argument check would impose a useless overhead for correctly
* implemented {@link Object#equals} methods. As a compromise we perform this check at runtime
* only if assertions are enabled. Using assertions for argument check in a public API is
* usually a deprecated practice, but we make an exception for this particular method.
* <p>
* <b>Note on method overloading:</b> This method could be selected by the compiler for
* comparing primitive types, because the compiler could perform an auto-boxing and get
* a result assignable to {@code Object}. However it should not occur in practice because
* overloaded (and more efficient) methods are provided for every primitive types. This is
* true even when the two arguments are different primitive type because of widening
* conversions. The only exception is when a {@code boolean} argument is mixed with a
* different primitive type.
*
* @param object1 The first object to compare, or {@code null}.
* @param object2 The second object to compare, or {@code null}.
* @return {@code true} if both objects are equal.
* @throws AssertionError If assertions are enabled and at least one argument is an array.
*/
public static boolean equals(final Object object1, final Object object2) throws AssertionError {
assert object1 == null || !object1.getClass().isArray() : object1;
assert object2 == null || !object2.getClass().isArray() : object2;
return (object1 == object2) || (object1 != null && object1.equals(object2));
}
/**
* Convenience method for testing two objects for equality. One or both objects may be null.
* If both are non-null and are arrays, then every array elements will be compared.
* <p>
* This method may be useful when the objects may or may not be array. If they are known
* to be arrays, consider using {@link Arrays#deepEquals(Object[],Object[])} or one of its
* primitive counter-part instead.
* <p>
* <strong>Rules for choosing an {@code equals} or {@code deepEquals} method</strong>
* <ul>
* <li>If <em>both</em> objects are declared as {@code Object[]} (not anything else like
* {@code String[]}), consider using {@link Arrays#deepEquals(Object[],Object[])} except
* if it is known that the array elements can never be other arrays.</li>
*
* <li>Otherwise if both objects are arrays (e.g. {@code Expression[]}, {@code String[]},
* {@code int[]}, <cite>etc.</cite>), use {@link Arrays#equals(Object[],Object[])}. This
* rule is applicable to arrays of primitive type too, since {@code Arrays.equals} is
* overriden with primitive counter-parts.</li>
*
* <li>Otherwise if at least one object is anything else than {@code Object} (e.g.
* {@code String}, {@code Expression}, <cite>etc.</cite>), use {@link #equals(Object,Object)}.
* Using this {@code deepEquals} method would be an overkill since there is no chance that
* {@code String} or {@code Expression} could be an array.</li>
*
* <li>Otherwise if <em>both</em> objects are declared exactly as {@code Object} type and
* it is known that they could be arrays, only then invoke this {@code deepEquals} method.
* In such case, make sure that the hash code is computed using {@link #deepHashCode} for
* consistency.</li>
* </ul>
*
* @param object1 The first object to compare, or {@code null}.
* @param object2 The second object to compare, or {@code null}.
* @return {@code true} if both objects are equal.
*/
public static boolean deepEquals(final Object object1, final Object object2) {
if (object1 == object2) {
return true;
}
if (object1 == null || object2 == null) {
return false;
}
if (object1 instanceof Object[]) {
return (object2 instanceof Object[]) &&
Arrays.deepEquals((Object[]) object1, (Object[]) object2);
}
if (object1 instanceof double[]) {
return (object2 instanceof double[]) &&
Arrays.equals((double[]) object1, (double[]) object2);
}
if (object1 instanceof float[]) {
return (object2 instanceof float[]) &&
Arrays.equals((float[]) object1, (float[]) object2);
}
if (object1 instanceof long[]) {
return (object2 instanceof long[]) &&
Arrays.equals((long[]) object1, (long[]) object2);
}
if (object1 instanceof int[]) {
return (object2 instanceof int[]) &&
Arrays.equals((int[]) object1, (int[]) object2);
}
if (object1 instanceof short[]) {
return (object2 instanceof short[]) &&
Arrays.equals((short[]) object1, (short[]) object2);
}
if (object1 instanceof byte[]) {
return (object2 instanceof byte[]) &&
Arrays.equals((byte[]) object1, (byte[]) object2);
}
if (object1 instanceof char[]) {
return (object2 instanceof char[]) &&
Arrays.equals((char[]) object1, (char[]) object2);
}
if (object1 instanceof boolean[]) {
return (object2 instanceof boolean[]) &&
Arrays.equals((boolean[]) object1, (boolean[]) object2);
}
return object1.equals(object2);
}
/**
* Alters the given seed with the hash code value computed from the given value.
*
* @param value The value whose hash code to compute.
* @param seed The hash code value computed so far. If this method is invoked for the first
* field, then any arbitrary value (preferrably different for each class) is okay.
* @return An updated hash code value.
*/
public static int hash(boolean value, int seed) {
// Use the same values than Boolean.hashCode()
return seed * PRIME_NUMBER + (value ? 1231 : 1237);
}
/**
* Alters the given seed with the hash code value computed from the given value.
*
* @param value The value whose hash code to compute.
* @param seed The hash code value computed so far. If this method is invoked for the first
* field, then any arbitrary value (preferably different for each class) is okay.
* @return An updated hash code value.
*/
public static int hash(char value, int seed) {
return seed * PRIME_NUMBER + (int) value;
}
/**
* Alters the given seed with the hash code value computed from the given value.
* {@code byte} and {@code short} primitive types are handled by this method as
* well through implicit widening conversion.
*
* @param value The value whose hash code to compute.
* @param seed The hash code value computed so far. If this method is invoked for the first
* field, then any arbitrary value (preferably different for each class) is okay.
* @return An updated hash code value.
*/
public static int hash(int value, int seed) {
return seed * PRIME_NUMBER + value;
}
/**
* Alters the given seed with the hash code value computed from the given value.
* {@code byte} and {@code short} primitive types are handled by this method as
* well through implicit widening conversion.
*
* @param value The value whose hash code to compute.
* @param seed The hash code value computed so far. If this method is invoked for the first
* field, then any arbitrary value (preferably different for each class) is okay.
* @return An updated hash code value.
*/
public static int hash(long value, int seed) {
return seed * PRIME_NUMBER + (((int) value) ^ ((int) (value >>> 32)));
}
/**
* Alters the given seed with the hash code value computed from the given value.
*
* @param value The value whose hash code to compute.
* @param seed The hash code value computed so far. If this method is invoked for the first
* field, then any arbitrary value (preferably different for each class) is okay.
* @return An updated hash code value.
*/
public static int hash(float value, int seed) {
return seed * PRIME_NUMBER + Float.floatToIntBits(value);
}
/**
* Alters the given seed with the hash code value computed from the given value.
*
* @param value The value whose hash code to compute.
* @param seed The hash code value computed so far. If this method is invoked for the first
* field, then any arbitrary value (preferably different for each class) is okay.
* @return An updated hash code value.
*/
public static int hash(double value, int seed) {
return hash(Double.doubleToLongBits(value), seed);
}
/**
* Alters the given seed with the hash code value computed from the given value. The givan
* object may be null. This method do <strong>not</strong> iterates recursively in array
* elements. If array needs to be hashed, use one of {@link Arrays} method or
* {@link #deepHashCode deepHashCode} instead.
* <p>
* <b>Note on assertions:</b> There is no way to ensure at compile time that this method
* is not invoked with an array argument, while doing so would usually be a program error.
* Performing a systematic argument check would impose a useless overhead for correctly
* implemented {@link Object#hashCode} methods. As a compromise we perform this check at
* runtime only if assertions are enabled. Using assertions for argument check in a public
* API is usually a deprecated practice, but we make an exception for this particular method.
*
* @param value The value whose hash code to compute, or {@code null}.
* @param seed The hash code value computed so far. If this method is invoked for the first
* field, then any arbitrary value (preferably different for each class) is okay.
* @return An updated hash code value.
* @throws AssertionError If assertions are enabled and the given value is an array.
*/
public static int hash(Object value, int seed) throws AssertionError {
seed *= PRIME_NUMBER;
if (value != null) {
assert !value.getClass().isArray() : value;
seed += value.hashCode();
}
return seed;
}
/**
* Returns a hash code for the specified object, which may be an array.
* This method returns one of the following values:
* <p>
* <ul>
* <li>If the supplied object is {@code null}, then this method returns 0.</li>
* <li>Otherwise if the object is an array of objects, then
* {@link Arrays#deepHashCode(Object[])} is invoked.</li>
* <li>Otherwise if the object is an array of primitive type, then the corresponding
* {@link Arrays#hashCode(double[]) Arrays.hashCode(...)} method is invoked.</li>
* <li>Otherwise {@link Object#hashCode()} is invoked.<li>
* </ul>
* <p>
* This method should be invoked <strong>only</strong> if the object type is declared
* exactly as {@code Object}, not as some subtype like {@code Object[]}, {@code String} or
* {@code float[]}. In the later cases, use the appropriate {@link Arrays} method instead.
*
* @param object The object to compute hash code. May be {@code null}.
* @return The hash code of the given object.
*/
public static int deepHashCode(final Object object) {
if (object == null) {
return 0;
}
if (object instanceof Object[]) {
return Arrays.deepHashCode((Object[]) object);
}
if (object instanceof double[]) {
return Arrays.hashCode((double[]) object);
}
if (object instanceof float[]) {
return Arrays.hashCode((float[]) object);
}
if (object instanceof long[]) {
return Arrays.hashCode((long[]) object);
}
if (object instanceof int[]) {
return Arrays.hashCode((int[]) object);
}
if (object instanceof short[]) {
return Arrays.hashCode((short[]) object);
}
if (object instanceof byte[]) {
return Arrays.hashCode((byte[]) object);
}
if (object instanceof char[]) {
return Arrays.hashCode((char[]) object);
}
if (object instanceof boolean[]) {
return Arrays.hashCode((boolean[]) object);
}
return object.hashCode();
}
/**
* Returns a string representation of the specified object, which may be an array.
* This method returns one of the following values:
* <p>
* <ul>
* <li>If the object is an array of objects, then
* {@link Arrays#deepToString(Object[])} is invoked.</li>
* <li>Otherwise if the object is an array of primitive type, then the corresponding
* {@link Arrays#toString(double[]) Arrays.toString(...)} method is invoked.</li>
* <li>Otherwise {@link String#valueOf(String)} is invoked.<li>
* </ul>
* <p>
* This method should be invoked <strong>only</strong> if the object type is declared
* exactly as {@code Object}, not as some subtype like {@code Object[]}, {@code Number} or
* {@code float[]}. In the later cases, use the appropriate {@link Arrays} method instead.
*
* @param object The object to format as a string. May be {@code null}.
* @return A string representation of the given object.
*/
public static String deepToString(final Object object) {
if (object instanceof Object[]) {
return Arrays.deepToString((Object[]) object);
}
if (object instanceof double[]) {
return Arrays.toString((double[]) object);
}
if (object instanceof float[]) {
return Arrays.toString((float[]) object);
}
if (object instanceof long[]) {
return Arrays.toString((long[]) object);
}
if (object instanceof int[]) {
return Arrays.toString((int[]) object);
}
if (object instanceof short[]) {
return Arrays.toString((short[]) object);
}
if (object instanceof byte[]) {
return Arrays.toString((byte[]) object);
}
if (object instanceof char[]) {
return Arrays.toString((char[]) object);
}
if (object instanceof boolean[]) {
return Arrays.toString((boolean[]) object);
}
return String.valueOf(object);
}
/**
* Returns a {@linkplain Queue queue} which is always empty and accepts no element.
*
* @param <E> The type of elements in the empty collection.
* @return An empty collection.
*
* @see Collections#emptyList
* @see Collections#emptySet
*/
@SuppressWarnings("unchecked")
public static <E> Queue<E> emptyQueue() {
return (Queue<E>) EMPTY_QUEUE;
}
/**
* Returns a string of the specified length filled with white spaces.
* This method tries to return a pre-allocated string if possible.
*
* @param length The string length. Negative values are clamped to 0.
* @return A string of length {@code length} filled with white spaces.
*/
public static String spaces(int length) {
/*
* No need to synchronize. In the unlikely event of two threads calling this method
* at the same time and the two calls creating a new string, the String.intern() call
* will take care of canonicalizing the strings.
*/
if (length < 0) {
length = 0;
}
String s;
if (length < spaces.length) {
s = spaces[length];
if (s == null) {
s = spaces[spaces.length - 1].substring(0, length).intern();
spaces[length] = s;
}
} else {
char[] blancs = new char[length];
Arrays.fill(blancs, ' ');
s = new String(blancs);
}
return s;
}
/**
* Makes sure that an argument is non-null.
*
* @param name Argument name.
* @param object User argument.
* @throws NullPointerException if {@code object} is null.
*/
public static void ensureNonNull(final String name, final Object object)
throws NullPointerException {
if (object == null) {
throw new NullPointerException(Errors.format(ErrorKeys.NULL_ARGUMENT_$1, name));
}
}
}