package umontreal.iro.lecuyer.probdist;
import java.lang.reflect.*;
import java.util.StringTokenizer;
/**
* This class implements a string API for the package probdist.
* It uses Java Reflection to allow the creation of probability distribution
* objects from a string. This permits one to obtain distribution specifications
* from a file or dynamically from user input during program execution.
* This string API is similar to that of
* UNURAN.
*
*
* The (static) methods of this class invoke the constructor specified
* in the string. For example,
*
*
*
* d = DistributionFactory.getContinuousDistribution ("NormalDist (0.0, 2.5)");
*
*
* is equivalent to
*
*
*
* d = NormalDist (0.0, 2.5);
*
*
*
*
* The string that specifies the distribution (i.e., the formal parameter
* str of the methods) must be a valid call of the constructor
* of a class that extends {@link ContinuousDistribution} or
* {@link DiscreteDistribution}, and all parameter values must be numerical
* values (variable names are not allowed).
*
*
*
*
* The distribution parameters can also be estimated from a set of observations
* instead of being passed to the constructor. In that case, one passes the
* vector of observations, and the constructor estimates the parameters by
* the maximum likelihood method.
*
*/
public class DistributionFactory {
private DistributionFactory() {} // ???? Utile?
public static Distribution getDistribution (String str) {
// Extracts the name of the distribution.
// If there is an open parenthesis, the name contains all the
// non-space characters preceeding it.If not,the name is the full string.
int i = 0;
str = str.trim();
int idx = str.indexOf ('(', i);
String distName;
if (idx == -1)
distName = str.substring (i).trim();
else
distName = str.substring (i, idx).trim();
// Try to find the class in probdist package.
Class distClass;
if (distName.equals ("String"))
throw new IllegalArgumentException ("Invalid distribution name: "
+ distName);
try {
distClass = Class.forName ("umontreal.iro.lecuyer.probdist."
+ distName);
}
catch (ClassNotFoundException e) {
// Look for a fully qualified classname whose constructor
// matches this string.
try {
distClass = Class.forName (distName);
// We must check if the class implements Distribution
if (Distribution.class.isAssignableFrom(distClass) == false)
throw new IllegalArgumentException
("The given class is not a Probdist distribution class.");
}
catch (ClassNotFoundException ex) {
throw new IllegalArgumentException ("Invalid distribution name: "
+ distName);
}
}
String paramStr = "";
if (idx != -1) {
// Get the parameters from the string.
int parFrom = idx;
int parTo = str.lastIndexOf (')');
// paramStr will contain the parameters without parentheses.
paramStr = str.substring (parFrom + 1, parTo).trim();
if (paramStr.indexOf ('(') != -1 || paramStr.indexOf (')') != -1)
//All params are numerical,so parenthesis nesting is forbidden here
throw new IllegalArgumentException ("Invalid parameter string: "
+ paramStr);
}
if (paramStr.equals ("")) {
// No parameter is given to the constructor.
try {
return (Distribution) distClass.newInstance();
}
catch (IllegalAccessException e) {
throw new IllegalArgumentException
("Default parameters not available");
}
catch (InstantiationException e) {
throw new IllegalArgumentException
("Default parameters not available");
}
}
// Find the number of parameters and try to find a matching constructor.
// Within probdist, there are no constructors with the same
// number of arguments but with different types.
// This simplifies the constructor selection scheme.
StringTokenizer paramTok = new StringTokenizer (paramStr, ",");
int nparams = paramTok.countTokens();
Constructor[] cons = distClass.getConstructors();
Constructor distCons = null;
Class[] paramTypes = null;
// Find a public constructor with the correct number of parameters.
for (i = 0; i < cons.length; i++) {
if (Modifier.isPublic (cons[i].getModifiers()) &&
((paramTypes = cons[i].getParameterTypes()).length == nparams)) {
distCons = cons[i];
break;
}
}
if (distCons == null)
throw new IllegalArgumentException ("Invalid parameter number");
// Create the parameters for the selected constructor.
Object[] instParams = new Object[nparams];
for (i = 0; i < nparams; i++) {
String par = paramTok.nextToken().trim();
try {
// We only need a limited set of parameter types here.
if (paramTypes[i] == int.class)
instParams[i] = new Integer (par);
else if (paramTypes[i] == long.class)
instParams[i] = new Long (par);
else if (paramTypes[i] == float.class) {
if (par.equalsIgnoreCase ("infinity") || par.equalsIgnoreCase
("+infinity"))
instParams[i] = new Float (Float.POSITIVE_INFINITY);
else if (par.equalsIgnoreCase ("-infinity"))
instParams[i] = new Float (Float.NEGATIVE_INFINITY);
else
instParams[i] = new Float (par);
}
else if (paramTypes[i] == double.class) {
if (par.equalsIgnoreCase ("infinity") || par.equalsIgnoreCase
("+infinity"))
instParams[i] = new Double (Double.POSITIVE_INFINITY);
else if (par.equalsIgnoreCase ("-infinity"))
instParams[i] = new Double (Double.NEGATIVE_INFINITY);
else
instParams[i] = new Double (par);
}
else
throw new IllegalArgumentException
("Parameter " + (i+1) + " type " + paramTypes[i].getName() +
"not supported");
}
catch (NumberFormatException e) {
throw new IllegalArgumentException
("Parameter " + (i+1) + " of type " +
paramTypes[i].getName()+" could not be converted from String");
}
}
// Try to instantiate the distribution class.
try {
return (Distribution) distCons.newInstance (instParams);
}
catch (IllegalAccessException e) {
return null;
}
catch (InstantiationException e) {
return null;
}
catch (InvocationTargetException e) {
return null;
}
}
@SuppressWarnings("unchecked")
/**
* Uses the Java Reflection API to construct a {@link ContinuousDistribution}
* object by estimating parameters of the distribution using the maximum likelihood
* method based on the n observations in table x[i],
* i = 0, 1,…, n - 1.
*
* @param distName the name of the distribution to instanciate
*
* @param x the list of observations to use to evaluate parameters
*
* @param n the number of observations to use to evaluate parameters
*
*
*/
public static ContinuousDistribution getDistributionMLE
(String distName, double[] x, int n) {
Class distClass;
try
{
distClass = Class.forName ("umontreal.iro.lecuyer.probdist." + distName);
}
catch (ClassNotFoundException e)
{
try
{
distClass = Class.forName (distName);
}
catch (ClassNotFoundException ex)
{
throw new IllegalArgumentException ("Invalid distribution name: "
+ distName);
}
}
return getDistributionMLE ((Class)distClass, x, n);
}
@SuppressWarnings("unchecked")
/**
* Uses the Java Reflection API to construct a {@link DiscreteDistributionInt}
* object by estimating parameters of the distribution using the maximum likelihood
* method based on the n observations in table x[i],
* i = 0, 1,…, n - 1.
*
* @param distName the name of the distribution to instanciate
*
* @param x the list of observations to use to evaluate parameters
*
* @param n the number of observations to use to evaluate parameters
*
*
*/
public static DiscreteDistributionInt getDistributionMLE
(String distName, int[] x, int n) {
Class distClass;
try
{
distClass = Class.forName ("umontreal.iro.lecuyer.probdist." + distName);
}
catch (ClassNotFoundException e)
{
try
{
distClass = Class.forName (distName);
}
catch (ClassNotFoundException ex)
{
throw new IllegalArgumentException ("Invalid distribution name: "
+ distName);
}
}
return getDistributionMLE ((Class)distClass, x, n);
}
@SuppressWarnings("unchecked")
/**
* Uses the Java Reflection API to construct a {@link ContinuousDistribution}
* object by estimating parameters of the distribution using the maximum likelihood
* method based on the n observations in table x[i],
* i = 0, 1,…, n - 1.
*
* @param distClass the class of the distribution to instanciate
*
* @param x the list of observations to use to evaluate parameters
*
* @param n the number of observations to use to evaluate parameters
*
*
*/
public static T getDistributionMLE
(Class distClass, double[] x, int n) {
if (ContinuousDistribution.class.isAssignableFrom(distClass) == false)
throw new IllegalArgumentException
("The given class is not a Probdist distribution class.");
Method m;
try
{
m = distClass.getMethod ("getInstanceFromMLE", double[].class, int.class);
}
catch (NoSuchMethodException e) {
throw new IllegalArgumentException
("The given class does not provide the static method getInstanceFromMLE (double[],int)");
}
if (!Modifier.isStatic (m.getModifiers()) ||
!distClass.isAssignableFrom (m.getReturnType()))
throw new IllegalArgumentException
("The given class does not provide the static method getInstanceFromMLE (double[],int)");
try
{
return (T)m.invoke (null, x, n);
}
catch (IllegalAccessException e) {
return null;
}
catch (IllegalArgumentException e) {
return null;
}
catch (InvocationTargetException e) {
return null;
}
}
@SuppressWarnings("unchecked")
/**
* Uses the Java Reflection API to construct a {@link DiscreteDistributionInt}
* object by estimating parameters of the distribution using the maximum likelihood
* method based on the n observations in table x[i],
* i = 0, 1,…, n - 1.
*
* @param distClass the class of the distribution to instanciate
*
* @param x the list of observations to use to evaluate parameters
*
* @param n the number of observations to use to evaluate parameters
*
*
*/
public static T getDistributionMLE
(Class distClass, int[] x, int n) {
if (DiscreteDistributionInt.class.isAssignableFrom(distClass) == false)
throw new IllegalArgumentException
("The given class is not a discrete distribution class over integers.");
Method m;
try
{
m = distClass.getMethod ("getInstanceFromMLE", int[].class, int.class);
}
catch (NoSuchMethodException e) {
throw new IllegalArgumentException
("The given class does not provide the static method getInstanceFromMLE (int[],int)");
}
if (!Modifier.isStatic (m.getModifiers()) ||
!distClass.isAssignableFrom (m.getReturnType()))
throw new IllegalArgumentException
("The given class does not provide the static method getInstanceFromMLE (int[],int)");
try
{
return (T)m.invoke (null, x, n);
}
catch (IllegalAccessException e) {
return null;
}
catch (IllegalArgumentException e) {
return null;
}
catch (InvocationTargetException e) {
return null;
}
}
/**
* Uses the Java Reflection API to construct a {@link ContinuousDistribution}
* object by executing the code contained in the string str.
* This code should be a valid invocation of the constructor of a
* {@link ContinuousDistribution} object.
* This method throws exceptions if it cannot parse the given string and
* returns null if the distribution object could not be created due to
* a Java-specific instantiation problem.
*
* @param str string that contains a call to the constructor of a continuous
* distribution
*
* @return a continuous distribution object or null if it could not
* be instantiated
* @exception IllegalArgumentException if parsing problems occured
* when reading str
*
* @exception ClassCastException if the distribution string does not represent
* a continuous distribution
*
*
*/
public static ContinuousDistribution getContinuousDistribution (String str) {
return (ContinuousDistribution)getDistribution (str);
}
/**
* Same as {@link #getContinuousDistribution getContinuousDistribution}, but for discrete distributions
* over the real numbers.
*
* @param str string that contains a call to the constructor of a discrete
* distribution
*
* @return a discrete distribution object, or null if it could not
* be instantiated
* @exception IllegalArgumentException if parsing problems occured when
* reading str
*
* @exception ClassCastException if the distribution string does not represent
* a discrete distribution
*
*
*/
public static DiscreteDistribution getDiscreteDistribution (String str) {
return (DiscreteDistribution)getDistribution (str);
}
/**
* Same as {@link #getContinuousDistribution getContinuousDistribution}, but for discrete distributions
* over the integers.
*
* @param str string that contains a call to the constructor of a discrete
* distribution
*
* @return a discrete distribution object, or null if it could not
* be instantiated
* @exception IllegalArgumentException if parsing problems occured when
* reading str
*
* @exception ClassCastException if the distribution string does not represent
* a discrete distribution
*
*/
public static DiscreteDistributionInt getDiscreteDistributionInt (String str) {
return (DiscreteDistributionInt)getDistribution (str);
}
}
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