The day after Black Friday and most folks are still at the WalMart so I'll take
a stab at some testcases
private E createElementByConstructor() {
try {
Constructor<E>[] constrArray = (Constructor<E>[])
elementClass
.getConstructors();
Constructor<E> constructor = null;
Class[] paramTypes = null;
for (Constructor<E> constr : constrArray) {
if (constructor == null) {
/*this is executed first which is fine */
constructor = constr;
paramTypes = constr.getParameterTypes();
/*constr ParameterType (Class) count (e.g. 0) is less than number of Classes
stored in local var paramTypes (e.g. 1) */
} else if (constr.getParameterTypes().length <
paramTypes.length) {
constructor = constr;
paramTypes = constr.getParameterTypes();
}
}/* Testcase execution 1st pass Class is Class1 with 1
parameter named fu*/
Class=Class1 parameter=fu
Constructor is now Class1(fu)
paramTypes.length is now 1
/* Testcase execution 2nd pass Class is Class2 with 0 parameters*/
Class=Class2 0 parameters so
constr.getParameterTypes().length()==0 < paramTypes 1
Constructor is now Class2();
paramTypes.length is now 0
/* Testcase execution 3rd pass Class is Class2 with 2 parameters parameter=fu
and parameter=bar */
Class3 parameter fu, parameter bar so
constr.getParameterTypes().length()==2 < paramTypes 0 FAILS!!!!
assignments to variables of constructor and paramTypes are bypassed
Constructor is STILL Class2();
paramTypes.length is STILL 0
is this what you intend?
Martin
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> Date: Sat, 27 Nov 2010 18:26:11 +0900
> Subject: Re: javax.servlet.ServletException: BeanUtils.populate
> From: [email protected]
> To: [email protected]
>
> I have dug it out from my old project.
>
> The code is not very beautiful, you can modify it if you wish,
> but please don't change the author information.
>
> Here is the code:
>
> ========================================
>
> package com.ewsoft.common.utils;
>
> import java.lang.reflect.Constructor;
> import java.util.ArrayList;
> import java.util.List;
>
> /**
> * A List class which can create items as need.<br />
> * When method get(index) and add(index, element) is called,<br />
> * and if there is no item in this index, item instances will be created
> * automatically to avoid a NullPointerException.
> *
> * @author Li Ying([email protected])
> */
> public class AutoList<E extends Object> extends ArrayList<E> {
> private Class<E> elementClass;
>
> public AutoList(final Class<E> elementClass) {
> super();
> this.elementClass = elementClass;
> }
>
> private void ensureSize(final int size) {
> synchronized (this) {
> while (this.size() < size) {
> add(createNewElement());
> }
> }
> }
>
> private E createElementByConstructor() {
> try {
> Constructor<E>[] constrArray = (Constructor<E>[])
> elementClass
> .getConstructors();
>
> Constructor<E> constructor = null;
> Class[] paramTypes = null;
>
> for (Constructor<E> constr : constrArray) {
> if (constructor == null) {
> constructor = constr;
> paramTypes = constr.getParameterTypes();
> } else if (constr.getParameterTypes().length <
> paramTypes.length) {
> constructor = constr;
> paramTypes = constr.getParameterTypes();
> }
> }
>
> List paramList = new ArrayList();
> for (int i = 0; i < paramTypes.length; i++) {
> paramList.add(null);
> }
>
> return constructor.newInstance(paramList.toArray());
> } catch (Exception e) {
> return null;
> }
> }
>
> private E createNewElement() {
> return createElementByConstructor();
> }
>
> /*
> * (non-Javadoc)
> *
> * @see java.util.ArrayList#get(int)
> */
> @Override
> public final E get(final int index) {
> ensureSize(index + 1);
>
> return super.get(index);
> }
>
> /*
> * (non-Javadoc)
> *
> * @see java.util.ArrayList#add(int, java.lang.Object)
> */
> @Override
> public final void add(final int index, final E element) {
> ensureSize(index);
>
> super.add(index, element);
> }
> }
>
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