We Keep Coding

What is this design (or anti-) pattern and more importantly is there a better way?

I'm receiving from a webservice a list of key-value pairs, and have inherited the following code:
public String iconValue = null;
... (over 50 class variables assigned in MyObject constructor below)
public MyObject(List<Attribute> attrs) {
String attrName, attrValue;
for (Attribute a : attrs) {
try
{
attrName = a.getName();
attrValue = a.getValue();
if (attrValue == null || "".equals(attrValue.trim()))
continue;
if (ICONS.equals(attrName)) {
//Do something including assignment
this.iconValue = attrValue;
}
else if (URL.equals(attrName))
{
//Do something including assignment
}
else if (...) A giant list of over 50 different attributes hardcoded
{
//Do something including assignment
}
...
So,except for keeping a hashmap - is there a better way than the above to keep hard coded variables within the class and use this "when-if" pattern.
Also,does this pattern have a name?

One way I can think about is to use ENUMs and dynamically dispatch the works to each of the ENUM object, instead of doing a huge if else, esp. since ENUMs can be looked up by their names.
That would be like a strategy pattern.
For example:
Implement an ENUM to have a method doJob() for each of the instances;
Use the valueOf() method to dispatch the works.
Code sample:
public enum Strategies {
URL {
#Override
public void doJob(MyObject mo) {
// do the work
}
},
ICONS {
#Override
public void doJob(MyObject mo) {
// another work
}
};
public abstract void doJob(MyObject mo);
}
And when using it,
try {
Strategies.valueOf(attrName).doJob();
} catch (IllegalArgumentException e) {
// ENUM does not exist, illegal parameter
}

If you want to take a different action for each possible value of attribute, you will end up with something about that verbose, I'm afraid. Some improvements though:
If you are using Java7 or above, you can now use switch statements with Strings (link)
If you are not, you could create an Enum that has a static method that returns an Enum element you could switch on. It's no performance improvement, but it might help with readability of your code.

Does this pattern have a name?
Nope.
In Java 7 you can express that as:
switch (attrName) {
case ICONS:
//Do something including assignment
break;
case URL:
//Do something including assignment
break;
// and so on
}
... provided that ICONS, URL and the other strings are compile-time constants.
That is more concise and more robust. It is also (probably) more efficient because the switch can most likely be implemented using hashing.

I don't think it has a name, but you could call it "using polymorphism wrong" (if type safety is a concern). It depends on whether you have a well defined data contract or not. Is the data you're receiving a proper object, or just "random" data?
If it's a proper object I would create a concrete representation and use something like Dozer (or if you don't want to be tied down wit dependency, roll your own mapper using reflection) to convert between them.
If it's more or less random data, I'd just use a Map, or similar data structure.

Copy Object of Any Type [duplicate]

This question already has answers here:
How do I copy an object in Java?
(23 answers)
Closed 9 years ago.
I have the following.
public static <T> T someMethod(T originalObject) {
T modifiedObject = /* copy of original object (HOW DO YOU DO THIS?) */
/* Some logic that modifies the object. */
...
return modifiedObject; // without changing original Object
}
The question is then, how to a create a copy of type T if you have no idea what type T could be?
REVISION - to be more clear I will just paste my code.
public class ObjectMerger {
public static <T> T merge(T original, T patch) throws IllegalArgumentException, IllegalAccessException {
Object mergedObject = original // TODO: implement a way to copy original
Field[] inheritedFields = patch.getClass().getFields();
Field[] memberFields = patch.getClass().getDeclaredFields();
Field[] allFields = (Field[]) ArrayUtils.addAll(inheritedFields, memberFields);
for (Field field : allFields) {
Boolean originalAccessibility = field.isAccessible();
field.setAccessible(true);
Object fieldValue = field.get(patch);
if (fieldValue != null) {
Boolean fieldIsFinal = Modifier.isFinal(field.getModifiers());
if (!fieldIsFinal) {
field.set(mergedObject, fieldValue);
}
}
field.setAccessible(originalAccessibility);
}
return mergedObject;
}
}
Note: I have tried saying T extends Cloneable and it's a no go. I believe that implementing Cloneable does not ensure clone is visible.
NOTE: NOTE A DUPLICATE!
For those marking this as a duplicate please read the question. This is asking for a way to duplicate an object of a unknown type. Anyways from what I have come to understand this is not possible. Thanks to everyone for your input.

If you have absolutely no information on what T is, the best you can do is to test if it implements Cloneable and .clone() it.
if (originalObject implements Cloneable) {
T modifiedObject = originalObject.clone();
// ...
} else {
throw new IllegalArgumentException();
}
You could also restrict T:
public static <T extends Cloneable> T someMethod(T originalObject) {
T modifiedObject = originalObject.clone();
}
In any case, how do you count on modifying an object that you have absolutely no idea on what it is? Your use case sounds a bit strange. It might be easier to help if you describe what you are trying to do (and not how you are trying to do it).

The question is then, how to a create a copy of type T if you have no idea what type T could be?
If you really have no idea what T is, you quite simply cannot make a copy.
Firstly, there's no universal API for copying objects (any given type may or may not support clone()).
However, the main reason is that T might not support copying at all. For example, what if T is FileInputStream? How do you expect to copy an instance of that?
Besides, how are you going to implement /* Some logic that modifies the object. */ if you have no idea what T is?

If you are ready to use XStream, here is the solution,
XStream xstream = new XStream();
return (T) xstream.fromXML(XSTREAM.toXML(originalObject));

As title says Copy Object of Any Type then I think only option you have is to use Reflection API. Also even if you use reflection you need to have some criteria depending on what you are creating a copy, like what attributes you want want to copy from source object etc.

There are two options:
Use the clone() and Cloneable as already suggested in other answer
If you do not want to restrict to Cloneable then use deep/shallow clone library which uses reflection. (Not recommended but still an option). Care should be taken that the object supports copying.

How do I perform an action on each element of a List and return the result (without affecting the original of course)?

How do I write a static method in Java that will take a List, perform an action on each element, and return the result (without affecting the original of course)?
For example, if I want to add 2 to each element what goes in the ... here? The concrete return type must be the same, e.g. if my List is a LinkedList with values 1,2,3 I should get back a LinkedList with values 3,4,5. Similarly for ArrayList, Vector, Stack etc, which are all Lists.
I can see how to do this using multiple if (lst instanceof LinkedList) ... etc... any better way?
import java.util.List;
public class ListAdd {
static List<Integer> add2 (List<Integer> lst) {
...
return result;
}
}

There are already many answers, but I'd like to show you a different way to think of this problem.
The operation you want to perform is known as map in the world of functional programming. It is something we do really all the time in functional languages.
Let M<A> be some kind of container (in your case, M would be List, and A would be Integer; however, the container can be lots of other things). Suppose you have a function that transforms As into Bs, that is, f: A -> B. Let's write this function as of type F<A, B>, to use a notation closer to Java. Note that you can have A = B, as in the example you give (in which A = B = Integer).
Then, the operation map is defined as follows:
M<B> map(M<A>, F<A, B>)
That is, the operation will return a M<B>, presumably by applying F<A, B> to each A in M<A>.
In practice...
There's a brilliant library developed by Google, called Guava, which brings lot's of functional idioms to Java.
In Guava, the map operation is called transform, and it can operate on any Iterable. It has also more specific implementations that work directly on lists, sets, etc.
Using Guava, the code you want to write would look like this:
static List<Integer> add2(List<Integer> ns) {
return Lists.transform(ns, new Function<Integer, Integer>() {
#Override Integer apply(Integer n) { return n + 2; }
}
}
Simple as that.
This code won't touch the original list, it will simply provide a new list that calculates its values as needed (that is, the values of the newly created list won't be calculated unless needed -- it's called a lazy operation).
As a final consideration, it is not possible for you to be absolutely sure that you will be able to return exactly the same implementation of List. And as many others pointed out, unless there's a very specific reason for this, you shouldn't really care. That's why List is an interface, you don't care about the implementation.

Fundamentally, the List interface doesn't make any guarantees that you'll have a way to duplicate it.
You may have some luck with various techniques:
Using clone() on the passed in List, although it may throw, or (since it is protected in Object) simply not be accessible
Use reflection to look for a public no-argument constructor on the passed-in List
Try to serialize and deserialize it in order to perform a "deep clone"
Create some sort of factory and build in knowledge of how to duplicate each different kind of List your code may encounter (What if it's a wrapper created by unmodifiableList(), or some oddball custom implementation backed by a RandomAccessFile?)
If all else fails, either throw, or return an ArrayList or a Vector for lack of better options

You could use reflection to look for a public zero-arg constructor on the result of lst.getClass() and then invoke() it to obtain the List into which you'll place your results. The Java Collections Framework recommends that any derivative of Collection offer a zero-arg constructor. That way, your results we be of the same runtime class as the argument.

Here is a variant which does neither copies nor modifies the original list. Instead, it wraps the original list by another object.
public List<Integer> add2(final List<Integer> lst) {
return new AbstractList<Integer>() {
public int size() {
return lst.size();
}
public Integer get(int index) {
return 2 + lst.get(index);
}
};
}
The returned list is not modifiable, but will change whenever the original list changes.
(This implements the iterator based on index access, thus it will be slow for a linked list. Then better implement it based on AbstractSequentialList.)
Of course, the resulting list will obviously not be of the same class as the original list.
Use this solution only if you really only need a read-only two added view of your original list, not if you want a modified copy with similar properties.

The whole point of using an interface, in this case List, is to abstract the fact that the implementation is hidden behind the interface.
Your intention is clear to me, however: the Clonable interface supports creating a new instance with the same state. This interface might not be defined on your List.
Often it's a good idea to rethink this situation: why do you need to clone the List in this place, this class? Shouldn't your list-creator be responsible for cloning the list? Or shouldn't the caller, who knows the type, make sure he passes in a clone of his list?
Probably, if you look for the semantics as you defined it, you can implement all your supported Lists:
static Vector<Integer> addTwo(Vector<Integer> vector) {
Vector<Integer> copy = null; // TODO: copy the vector
return addTwo_mutable(copy);
}
static ArrayList<Integer> addTwo(ArrayList<Integer> aList) {
ArrayList<Integer> copy = null; // TODO: copy the array list
return addTwo_mutable(copy);
}
static LinkedList<Integer> addTwo(LinkedList<Integer> lList) {
LinkedList<Integer> copy = null; // TODO: copy the linked list
return addTwo_mutable(copy);
}
private <T extends List<Integer>> static T addTwo_mutable(T list) {
return list; // TODO: implement
}
Even, when you don't support a data-type, you'll get a nice compiler error that the specified method does not exists.
(code not tested)

Just to show you that what you want to do is not possible in the general case, consider the following class:
final class MyList extends ArrayList<Integer> {
private MyList() {
super.add(1);
super.add(2);
super.add(3);
}
private static class SingletonHolder {
private static final MyList instance = new MyList();
}
public static MyList getInstance() {
return SingletonHolder.instance;
}
}
It is a singleton (also, a lazy, thread-safe singleton by the way), it's only instance can be obtained from MyList.getInstance(). You cannot use reflection reliably (because the constructor is private; for you to use reflection, you'd have to rely on proprietary, non-standard, non-portable APIs, or on code that could break due to a SecurityManager). So, there's no way for you to return a new instance of this list, with different values.
It's final as well, so that you cannot return a child of it.
Also, it would be possible to override every method of ArrayList that would modify the list, so that it would be really an immutable singleton.
Now, why would you want to return the exact same implementation of List?

OK well someone mentioned reflection. It seems to be an elegant solution:
import java.util.*;
public class ListAdd {
static List<Integer> add2 (List<Integer> lst) throws Exception {
List<Integer> result = lst.getClass().newInstance();
for (Integer i : lst) result.add(i + 2);
return result;
}
}
Concise, but it thows an checked exception, which is not nice.
Also, wouldn't it be nicer if we could use the method on concrete types as well, e.g. if a is an ArrayList with values 1, 2, 3, we could call add2(a) and get an ArrayList back? So in an improved version, we could make the signature generic:
static <T extends List<Integer>> T add2 (T lst) {
T res;
try {
res = (T) lst.getClass().newInstance();
} catch (InstantiationException e) {
throw new IllegalArgumentException(e);
} catch (IllegalAccessException e) {
throw new RuntimeException(e);
}
for (Integer i : lst) res.add(i + 2);
return res;
}
I think throwing a runtime exception is the least worst option if a list without a nullary construcor is passed in. I don't see a way to ensure that it does. (Java 8 type annotations to the rescue maybe?) Returning null would be kind of useless.
The downside of using this signature is that we can't return an ArrayList etc as the default, as we could have done as an alternative to throwing an exception, since the return type is guaranteed to be the same type as that passed in. However, if the user actually wants an ArrayList (or some other default type) back, he can make an ArrayList copy and use the method on that.
If anyone with API design experience reads this, I would be interested to know your thoughts on which is the preferable option: 1) returning a List that needs to be explicity cast back into the original type, but enabling a return of a different concrete type, or 2) ensuring the return type is the same (using generics), but risking exceptions if (for example) a singleton object without a nullary constructor is passed in?

An Hashmap with a finite set of keys that each accept only one type of value?

Ok, this might be a little hard to explain. I'm looking for a way to build a Hashmap of some sort, which will be populated with keys that I already know (because they are properties of the object I am creating). Each of these known keys will have values that are either a String, an int or float (which will be autoboxed), or - later - some kind of object/ function (I still don't know how I'll do that part, but it'll be further along the way anyway). I also want to set which type accepts each of the key (say key "x" will only accept an Integer type of value, key "equation" will only accept a string, etc.).
Just to give more context, my goal is to build a Tweener utility, as I found no such library in Java, except for SumoTween, that doesn't fit my needs at all. I'm kind of trying to build my classes the way Caurina is. If you have a better alternative that would save me time and trouble, please feel free to share (be it about Tweeners or about my Hashmap question). By the way, I'm doing this Tweener to use it in an Android game I'm building, in order to do animations on bitmap/drawable objects (can't use the animation classes for those afaik).
PS : This is my first question on this website, I hope I don't sound too confused; Please bear with me.

Why are you using a hashmap for this? If you have known "keys", just make a class with those members and then you can type them however you want.
If you really must use a hashmap for some reason, you can just extend it and override the put() method to check for your magic values. But I strongly recommend against that, it's poor design.

If I understand you correctly, you are basically looking for a HashMap. Is that correct?
PS Yes, I know that using "Object" that way isn't very pretty.

I'm not entirely sure if this is what you're asking for, but it sounds like you could use some kind of interface/abstract class for the key and implement/extend it appropriately for each key type, e.g.:
public interface Key {}
private static final class StringKey implements Key {
private final String value;
public StringKey(String value) {
this.value = value;
}
// hashCode, equals here
}
// IntegerKey, FloatKey, etc similarly
Then have something like:
HashMap<Key, Integer> map = new HashMap<Key, Integer>();

I'd say create a custom class that inherits from say HashMap, on insert you check the specified key/value if it's valid.
public static final HashMap<String, Class<?>> allowedTypes = new HashMap<String, Class<?>>() {{
put("key1", String.class);
put("key2", Integer.class);
// etc
}};
public class CustomHashMap extends HashMap {
public Object put(Object key, Object value) {
Class<?> type = allowedTypes(key);
if(type != null && !type.isInstance(value))
throw new IllegalArgumentException("Invalid type for key " + key);
return put(key, value);
}
private void PutAll(Map m) {
for(Entry<?, ?> entry : m.entrySet())
put(entry.getKey(), entry.getValue());
}
}

You could have separate maps, one for the Strings; another for the Integers, etc. And when adding to any of these maps, you could add the key to a (global) set, to ensure that no key is duplicated across maps. I suspect that wouldn't meet your needs very well (and of course the lookup is a little more involved), but if it works for you, great.
Maybe a better option is to add another level of indirection. Make your map a Hashmap where YourThing has subclasses for each of the types you want to hold. So, a StringYourThing has a String data member; an IntegerYourThing has an int data member, etc. I wouldn't be surprised to find that YourThing starts to take on functionality that is currently a switch statement somewhere inside another class that is trying to deal consistently with all these different data types. If that class could simply interact with a YourThing, it could get simpler. But it's hard to know without seeing your code.

I would rather avoid using map directly. What you are looking for is probably something more application specific:
Assume the whole thing you are building is for bunch of settings. Your "Setting" will have a predefined set of key. Each key is predefined to accept corresponding setting value of specific value. If incorrect type is provided, exception will be thrown.
I think something roughly like this is reasonable:
enum SettingValueType {
public boolean isCorrectType(Object obj) {
return true if obj is correct type represented by this enum
}
STRING, INT, FLOAT // add support to other type if u want
};
clsss SettingValue {
SettingValueType type;
Object value;
}
class SettingRepo { // a repository of setting entries
private Map<String, SettingValueType> allowedKeyAndType;
private Map<String, Object> settings;
SettingRepo() {
// setup allowedKeyAndType programmatically or from config etc, depends on your design
}
public SettingValue setSetting(String key, Object value) {
SettingValueType valueType = allowedKeyAndType.get(key);
if (valueType == null) {
throw new KeyNotAllowedException();
}
if (v!alueType.isCorrectType(value) {
throw new ValueIncorectTypeException();
}
return settings.put(key, new SettingValue(valueType, value));
}
}
public SettingValue getSetting(String key) {
// u may throw exception if key is not in predefined set
return settings.get(key);
}
// u may consider adding some convinient methods too:
public String setStringSetting(String key, String value) {
if alllowedKeyAndType do not contains key {
throw KeyNOtAllowedException
}
if type is not STRING {
throw IncorrectTypeExceptin
}
settings.put(key, new SettingValue(STRING, value))
}
public String getStringSetting(String key) {
// should be straight forward now, right?
}
}
There are lots of place that can be improved according to your usage:
if ur types are very dynamic, u may make SettingValueType something like a bunch of strategies, or use Class directly. setSetting() can made generic and take Class as extra parameter etc. But at least, this should give u a starting point.

java: How can I do dynamic casting of a variable from one type to another?

I would like to do dynamic casting for a Java variable, the casting type is stored in a different variable.
This is the regular casting:
String a = (String) 5;
This is what I want:
String theType = 'String';
String a = (theType) 5;
Is this possible, and if so how? Thanks!
Update
I'm trying to populate a class with a HashMap that I received.
This is the constructor:
public ConnectParams(HashMap<String,Object> obj) {
for (Map.Entry<String, Object> entry : obj.entrySet()) {
try {
Field f = this.getClass().getField(entry.getKey());
f.set(this, entry.getValue()); /* <= CASTING PROBLEM */
} catch (NoSuchFieldException ex) {
log.error("did not find field '" + entry.getKey() + '"');
} catch (IllegalAccessException ex) {
log.error(ex.getMessage());
}
}
}
The problem here is that some of the class' variables are of type Double, and if the number 3 is received it sees it as Integer and I have type problem.

Yes it is possible using Reflection
Object something = "something";
String theType = "java.lang.String";
Class<?> theClass = Class.forName(theType);
Object obj = theClass.cast(something);
but that doesn't make much sense since the resulting object must be saved in a variable of Object type. If you need the variable be of a given class, you can just cast to that class.
If you want to obtain a given class, Number for example:
Object something = new Integer(123);
String theType = "java.lang.Number";
Class<? extends Number> theClass = Class.forName(theType).asSubclass(Number.class);
Number obj = theClass.cast(something);
but there is still no point doing it so, you could just cast to Number.
Casting of an object does NOT change anything; it is just the way the compiler treats it.
The only reason to do something like that is to check if the object is an instance of the given class or of any subclass of it, but that would be better done using instanceof or Class.isInstance().
Update
according your last update the real problem is that you have an Integer in your HashMap that should be assigned to a Double. What you can do in this case, is check the type of the field and use the xxxValue() methods of Number
...
Field f = this.getClass().getField(entry.getKey());
Object value = entry.getValue();
if (Integer.class.isAssignableFrom(f.getType())) {
value = Integer.valueOf(((Number) entry.getValue()).intValue());
} else if (Double.class.isAssignableFrom(f.getType())) {
value = Double.valueOf(((Number) entry.getValue()).doubleValue());
} // other cases as needed (Long, Float, ...)
f.set(this, value);
...
(not sure if I like the idea of having the wrong type in the Map)

You'll need to write sort of ObjectConverter for this. This is doable if you have both the object which you want to convert and you know the target class to which you'd like to convert to. In this particular case you can get the target class by Field#getDeclaringClass().
You can find here an example of such an ObjectConverter. It should give you the base idea. If you want more conversion possibilities, just add more methods to it with the desired argument and return type.

Regarding your update, the only way to solve this in Java is to write code that covers all cases with lots of if and else and instanceof expressions. What you attempt to do looks as if are used to program with dynamic languages. In static languages, what you attempt to do is almost impossible and one would probably choose a totally different approach for what you attempt to do. Static languages are just not as flexible as dynamic ones :)
Good examples of Java best practice are the answer by BalusC (ie ObjectConverter) and the answer by Andreas_D (ie Adapter) below.
That does not make sense, in
String a = (theType) 5;
the type of a is statically bound to be String so it does not make any sense to have a dynamic cast to this static type.
PS: The first line of your example could be written as Class<String> stringClass = String.class; but still, you cannot use stringClass to cast variables.

You can do this using the Class.cast() method, which dynamically casts the supplied parameter to the type of the class instance you have. To get the class instance of a particular field, you use the getType() method on the field in question. I've given an example below, but note that it omits all error handling and shouldn't be used unmodified.
public class Test {
public String var1;
public Integer var2;
}
public class Main {
public static void main(String[] args) throws Exception {
Map<String, Object> map = new HashMap<String, Object>();
map.put("var1", "test");
map.put("var2", 1);
Test t = new Test();
for (Map.Entry<String, Object> entry : map.entrySet()) {
Field f = Test.class.getField(entry.getKey());
f.set(t, f.getType().cast(entry.getValue()));
}
System.out.println(t.var1);
System.out.println(t.var2);
}
}

You can write a simple castMethod like the one below.
private <T> T castObject(Class<T> clazz, Object object) {
return (T) object;
}
In your method you should be using it like
public ConnectParams(HashMap<String,Object> object) {
for (Map.Entry<String, Object> entry : object.entrySet()) {
try {
Field f = this.getClass().getField(entry.getKey());
f.set(this, castObject(entry.getValue().getClass(), entry.getValue()); /* <= CASTING PROBLEM */
} catch (NoSuchFieldException ex) {
log.error("did not find field '" + entry.getKey() + '"');
} catch (IllegalAccessException ex) {
log.error(ex.getMessage());
}
}
}

It works and there's even a common pattern for your approach: the Adapter pattern. But of course, (1) it does not work for casting java primitives to objects and (2) the class has to be adaptable (usually by implementing a custom interface).
With this pattern you could do something like:
Wolf bigBadWolf = new Wolf();
Sheep sheep = (Sheep) bigBadWolf.getAdapter(Sheep.class);
and the getAdapter method in Wolf class:
public Object getAdapter(Class clazz) {
if (clazz.equals(Sheep.class)) {
// return a Sheep implementation
return getWolfDressedAsSheep(this);
}
if (clazz.equals(String.class)) {
// return a String
return this.getName();
}
return null; // not adaptable
}
For you special idea - that is impossible. You can't use a String value for casting.

Your problem is not the lack of "dynamic casting". Casting Integer to Double isn't possible at all. You seem to want to give Java an object of one type, a field of a possibly incompatible type, and have it somehow automatically figure out how to convert between the types.
This kind of thing is anathema to a strongly typed language like Java, and IMO for very good reasons.
What are you actually trying to do? All that use of reflection looks pretty fishy.

Don't do this. Just have a properly parameterized constructor instead. The set and types of the connection parameters are fixed anyway, so there is no point in doing this all dynamically.

For what it is worth, most scripting languages (like Perl) and non-static compile-time languages (like Pick) support automatic run-time dynamic String to (relatively arbitrary) object conversions. This CAN be accomplished in Java as well without losing type-safety and the good stuff statically-typed languages provide WITHOUT the nasty side-effects of some of the other languages that do evil things with dynamic casting. A Perl example that does some questionable math:
print ++($foo = '99'); # prints '100'
print ++($foo = 'a0'); # prints 'a1'
In Java, this is better accomplished (IMHO) by using a method I call "cross-casting".
With cross-casting, reflection is used in a lazy-loaded cache of constructors and methods that are dynamically discovered via the following static method:
Object fromString (String value, Class targetClass)
Unfortunately, no built-in Java methods such as Class.cast() will do this for String to BigDecimal or String to Integer or any other conversion where there is no supporting class hierarchy. For my part, the point is to provide a fully dynamic way to achieve this - for which I don't think the prior reference is the right approach - having to code every conversion. Simply put, the implementation is just to cast-from-string if it is legal/possible.
So the solution is simple reflection looking for public Members of either:
STRING_CLASS_ARRAY = (new Class[] {String.class});
a) Member member = targetClass.getMethod(method.getName(),STRING_CLASS_ARRAY);
b) Member member = targetClass.getConstructor(STRING_CLASS_ARRAY);
You will find that all of the primitives (Integer, Long, etc) and all of the basics (BigInteger, BigDecimal, etc) and even java.regex.Pattern are all covered via this approach. I have used this with significant success on production projects where there are a huge amount of arbitrary String value inputs where some more strict checking was needed. In this approach, if there is no method or when the method is invoked an exception is thrown (because it is an illegal value such as a non-numeric input to a BigDecimal or illegal RegEx for a Pattern), that provides the checking specific to the target class inherent logic.
There are some downsides to this:
1) You need to understand reflection well (this is a little complicated and not for novices).
2) Some of the Java classes and indeed 3rd-party libraries are (surprise) not coded properly. That is, there are methods that take a single string argument as input and return an instance of the target class but it isn't what you think... Consider the Integer class:
static Integer getInteger(String nm)
Determines the integer value of the system property with the specified name.
The above method really has nothing to do with Integers as objects wrapping primitives ints.
Reflection will find this as a possible candidate for creating an Integer from a String incorrectly versus the decode, valueof and constructor Members - which are all suitable for most arbitrary String conversions where you really don't have control over your input data but just want to know if it is possible an Integer.
To remedy the above, looking for methods that throw Exceptions is a good start because invalid input values that create instances of such objects should throw an Exception. Unfortunately, implementations vary as to whether the Exceptions are declared as checked or not. Integer.valueOf(String) throws a checked NumberFormatException for example, but Pattern.compile() exceptions are not found during reflection lookups. Again, not a failing of this dynamic "cross-casting" approach I think so much as a very non-standard implementation for exception declarations in object creation methods.
If anyone would like more details on how the above was implemented, let me know but I think this solution is much more flexible/extensible and with less code without losing the good parts of type-safety. Of course it is always best to "know thy data" but as many of us find, we are sometimes only recipients of unmanaged content and have to do the best we can to use it properly.
Cheers.

So, this is an old post, however I think I can contribute something to it.
You can always do something like this:
package com.dyna.test;
import java.io.File;
import java.lang.reflect.Constructor;
public class DynamicClass{
#SuppressWarnings("unchecked")
public Object castDynamicClass(String className, String value){
Class<?> dynamicClass;
try
{
//We get the actual .class object associated with the specified name
dynamicClass = Class.forName(className);
/* We get the constructor that received only
a String as a parameter, since the value to be used is a String, but we could
easily change this to be "dynamic" as well, getting the Constructor signature from
the same datasource we get the values from */
Constructor<?> cons =
(Constructor<?>) dynamicClass.getConstructor(new Class<?>[]{String.class});
/*We generate our object, without knowing until runtime
what type it will be, and we place it in an Object as
any Java object extends the Object class) */
Object object = (Object) cons.newInstance(new Object[]{value});
return object;
}
catch (Exception e)
{
e.printStackTrace();
}
return null;
}
public static void main(String[] args)
{
DynamicClass dynaClass = new DynamicClass();
/*
We specify the type of class that should be used to represent
the value "3.0", in this case a Double. Both these parameters
you can get from a file, or a network stream for example. */
System.out.println(dynaClass.castDynamicClass("java.lang.Double", "3.0"));
/*
We specify a different value and type, and it will work as
expected, printing 3.0 in the above case and the test path in the one below, as the Double.toString() and
File.toString() would do. */
System.out.println(dynaClass.castDynamicClass("java.io.File", "C:\\testpath"));
}
Of course, this is not really dynamic casting, as in other languages (Python for example), because java is a statically typed lang. However, this can solve some fringe cases where you actually need to load some data in different ways, depending on some identifier. Also, the part where you get a constructor with a String parameter could be probably made more flexible, by having that parameter passed from the same data source. I.e. from a file, you get the constructor signature you want to use, and the list of values to be used, that way you pair up, say, the first parameter is a String, with the first object, casting it as a String, next object is an Integer, etc, but somehwere along the execution of your program, you get now a File object first, then a Double, etc.
In this way, you can account for those cases, and make a somewhat "dynamic" casting on-the-fly.
Hope this helps anyone as this keeps turning up in Google searches.

Try this for Dynamic Casting. It will work!!!
String something = "1234";
String theType = "java.lang.Integer";
Class<?> theClass = Class.forName(theType);
Constructor<?> cons = theClass.getConstructor(String.class);
Object ob = cons.newInstance(something);
System.out.println(ob.equals(1234));

I recently felt like I had to do this too, but then found another way which possibly makes my code look neater, and uses better OOP.
I have many sibling classes that each implement a certain method doSomething(). In order to access that method, I would have to have an instance of that class first, but I created a superclass for all my sibling classes and now I can access the method from the superclass.
Below I show two ways alternative ways to "dynamic casting".
// Method 1.
mFragment = getFragmentManager().findFragmentByTag(MyHelper.getName(mUnitNum));
switch (mUnitNum) {
case 0:
((MyFragment0) mFragment).sortNames(sortOptionNum);
break;
case 1:
((MyFragment1) mFragment).sortNames(sortOptionNum);
break;
case 2:
((MyFragment2) mFragment).sortNames(sortOptionNum);
break;
}
and my currently used method,
// Method 2.
mSuperFragment = (MySuperFragment) getFragmentManager().findFragmentByTag(MyHelper.getName(mUnitNum));
mSuperFragment.sortNames(sortOptionNum);

Just thought I would post something that I found quite useful and could be possible for someone who experiences similar needs.
The following method was a method I wrote for my JavaFX application to avoid having to cast and also avoid writing if object x instance of object b statements every time the controller was returned.
public <U> Optional<U> getController(Class<U> castKlazz){
try {
return Optional.of(fxmlLoader.<U>getController());
}catch (Exception e){
e.printStackTrace();
}
return Optional.empty();
}
The method declaration for obtaining the controller was
public <T> T getController()
By using type U passed into my method via the class object, it could be forwarded to the method get controller to tell it what type of object to return. An optional object is returned in case the wrong class is supplied and an exception occurs in which case an empty optional will be returned which we can check for.
This is what the final call to the method looked like (if present of the optional object returned takes a Consumer
getController(LoadController.class).ifPresent(controller->controller.onNotifyComplete());