Java Class New Instance newInstance(Class constructorClass, Object[] parameters)

Description

Searches for the correct constructor and instantiates a new object with the given parameters.

License

Open Source License

Parameter

Parameter	Description
constructorClass	the class that contains the constructor
parameters	the parameters for the constructor

Exception

Parameter	Description
IllegalAccessException	an exception
InstantiationException	an exception
InvocationTargetException	an exception
IllegalArgumentException	an exception

Return

a new instance created with the correct constructor

Declaration

public static Object newInstance(Class constructorClass, Object[] parameters) throws InstantiationException,
        IllegalAccessException, IllegalArgumentException, InvocationTargetException 

Method Source Code

//package com.java2s;
/*//from ww w. j  a  va2 s .  c om
 * Created on 16-Jul-2004 at 02:57:35.
 * 
 * Copyright (c) 2004-2005 Robert Virkus / Enough Software
 *
 * This file is part of J2ME Polish.
 *
 * J2ME Polish is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 * 
 * J2ME Polish 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 General Public License for more details.
 * 
 * You should have received a copy of the GNU General Public License
 * along with J2ME Polish; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 * 
 * Commercial licenses are also available, please
 * refer to the accompanying LICENSE.txt or visit
 * http://www.j2mepolish.org for details.
 */

import java.lang.reflect.Constructor;

import java.lang.reflect.InvocationTargetException;

import java.util.HashMap;

public class Main {
    private final static HashMap PRIMITIVE_CLASS_WRAPPERS = new HashMap();

    /**
     * Searches for the correct constructor and instantiates a new object with the given parameters.
     * @param constructorClass the class that contains the constructor
     * @param parameters the parameters for the constructor
     * @return a new instance created with the correct constructor
     * @throws IllegalAccessException 
     * @throws InstantiationException 
     * @throws InvocationTargetException 
     * @throws IllegalArgumentException 
     */
    public static Object newInstance(Class constructorClass, Object[] parameters) throws InstantiationException,
            IllegalAccessException, IllegalArgumentException, InvocationTargetException {
        if (parameters == null || parameters.length == 0) {
            return constructorClass.newInstance();
        }
        Constructor[] constructors = constructorClass.getConstructors();
        for (int i = 0; i < constructors.length; i++) {
            Constructor constructor = constructors[i];
            if (constructorFits(constructor, parameters)) {
                return constructor.newInstance(parameters);
            }
        }
        throw new IllegalArgumentException("Found no matching constructor in class " + constructorClass.getName()
                + " for parameters " + parameters.length);
    }

    /**
     * @param constructor
     * @param parameters
     * @return true when the contructor fits
     */
    public static boolean constructorFits(Constructor constructor, Object[] parameters) {
        return signatureFits(constructor.getParameterTypes(), parameters);
    }

    /**
     * @param parameterTypes
     * @param parameters
     * @return true when the signature fits
     */
    private static boolean signatureFits(Class[] parameterTypes, Object[] parameters) {
        if ((parameterTypes == null && parameters != null) || (parameterTypes != null && parameters == null)) {
            return false;
        }
        if (parameterTypes != null && parameters != null && parameterTypes.length != parameters.length) {
            return false;
        }
        if (parameterTypes == null && parameters == null) {
            return true;
        }
        for (int i = 0; i < parameters.length; i++) {
            Object parameter = parameters[i];
            Class parameterType = parameterTypes[i];
            if (parameter == null) {
                if (parameterType.isPrimitive()) {
                    return false;
                }
                continue; // null fits any class
            }
            Class parameterClass = parameter.getClass();
            if (!(parameterType.isAssignableFrom(parameterClass)
                    || (parameterType.isPrimitive() && isCompatible(parameterType, parameterClass)))) {
                //            System.out.println("- signature-mismatch: wanted=" + parameterType + ", have=" + parameter.getClass() );
                return false;
                //         } else {
                //            System.out.println("+ signature-match: wanted=" + parameterType + ", have=" + parameter.getClass() );
            }
        }
        return true;
    }

    /**
     * @param parameterType
     * @param parameterClass
     * @return
     */
    private static boolean isCompatible(Class parameterType, Class parameterClass) {
        Class wrapperClass = (Class) PRIMITIVE_CLASS_WRAPPERS.get(parameterType);
        if (wrapperClass != null) {
            return wrapperClass.isAssignableFrom(parameterClass);
        }
        return false;
    }
}

Related

1. newInstance(Class clazz)
2. newInstance(Class clazzName)
3. newInstance(Class cls)
4. newInstance(Class cls)
5. newInstance(Class cmdClass)
6. newInstance(Class klass)
7. newInstance(Class targetClass)
8. newInstance(Class cl, Object[] args)
9. newInstance(Class clazz)