Develop Reference

How to assert the number of assertions (or some other way to enforce that all members have been tested in an assertion)?

In a certain unit test for my class, I want to assert that an assertion has been written for all member fields. That is, given
public class Foo {
int a;
int b;
String c;
}
I want to do something like
#Test
public void testFieldsAgainstExternalModel(Foo model, Bar externalModel) {
assertEquals(model.a, externalModel.getA());
assertEquals(model.b, externalModel.getSomethingNamedDifferently());
assertEquals(model.c, externalModel.getC().toString());
assertNumberOfAssertionsInThisTest(3); // <-- How do I do this?
}
Of course, counting the number of assertions doesn't ensure that they had anything to do with each field having an assertion. But, I'm just trying to write a test that fails if a developer adds a field to Foo and forgets to update this test.
Naivest approach: The simplest thing I can think of is to use reflection to assert the number of fields Foo has, e.g. assertEquals(3, Foo.getDeclaredFields().count()). But, I can easily see a programmer bumping up the number without actually adding an assertion.
Still a naive approach, but acceptable: I think if I can at least count the number of assertions, it would sufficiently guide programmers toward the intended need.
More exact approaches: Of course it seems to best approach is to actual keep a table of which fields have appeared in the assertion (e.g. through a wrapper method like assertEqualsWithCounters), but in reality my situation's a little more complicated. For example, my model is actually a generated class (#AutoMatter) and I'll be using getters on both sides of the assertion, so it'll be hard to infer truly which field has been "touched" by an assertion. That's why just counting assertions and remaining agnostic to actual types and counts, would be easiest for me.

But, I'm just trying to write a test that fails if a developer adds a
field to Foo and forgets to update this test.
My company uses a mapping framework to map beans from the db, fields are one to one with the database, to a model bean we return to the client that we can modify as needed. I believe this is a common use case and essentially what you are trying to get at. You should be less concerned with testing changes to Foo, and more concerned with ensuring nothing breaks with the mapping from Foo to Bar.
Class BeanDb{
private int a;
private int b;
...
}
Class Bean{
private int a;
private int b;
private String somethingElse;
...
}
Then we have have a proivder test that uses isEqualToComparingFieldByFieldRecursively to compare the two beans.
private Bean bean = new Bean();
private Bean beanDb = new BeanDb();
private BeanProvider provider = new BeanProvider();
#Before
public void setup(){
bean.setA(1);
bean.setB(2);
beanDb.setA(1);
beanDb.setB(2);
}
#Test
public void prepareForDatabase(){
BeanDb db = provider.prepareForDatabase(bean);
assertThat(beanDb).isEqualToComparingFieldByFieldRecursively(db);
}
#Test
public void populateFromDatabase(){
Bean model = provider.populateFromDatabase(beanDb);
assertThat(model).isEqualToComparingFieldByFieldRecursively(bean);
}
This actually catches a lot of bugs. If something changes in the model bean / db bean the test will break in our continuous integrations suite. The caveat here is that isEqualToComparingFieldByFieldRecursively will not catch newly added fields.
When I review code / pull requests and BeanDb or the provider has been updated I ask, "Did you update the provider test?"

I think you may need to use PowerMockito as Mockito does not support mocking static methods.
I haven't tested the code below - but my idea would be to do the following:
#RunWith(PowerMockRunner.class)
public class Tester {
public class Foo {
int a = 5;
int b = 6;
String c = "7";
}
class Bar {
public int getA() {
return 5;
}
public int getSomethingNamedDifferently() {
return 6;
}
public Integer getC() {
return 7;
}
}
#Test
public void testFieldsAgainstExternalModel() {
testFieldsAgainstExternalModel(new Foo(), new Bar());
}
public void testFieldsAgainstExternalModel(Foo model, Bar externalModel) {
Assert spiedAssert = PowerMockito.spy(Assert.class);
spiedAssert.assertEquals(model.a, externalModel.getA());
spiedAssert.assertEquals(model.b, externalModel.getSomethingNamedDifferently());
spiedAssert.assertEquals(model.c, externalModel.getC().toString());
PowerMockito.verify(spiedAssert, times(3)).assertEquals(any(), any());
}
}

I think that the answer to
assertNumberOfAssertionsInThisTest(3); // <-- How do I do this?
is: you do not do that. This test is close to useless.
If there are only 3 fields, you can see with your eyes that you are checking those three fields. You are probably thinking about 15 fields in that class, but then:
assertEquals(model.a, externalModel.getA());
assertEquals(model.b, externalModel.getSomethingNamedDifferently());
assertEquals(model.c, externalModel.getC().toString());
assertEquals(model.c, externalModel.getC().toString());
assertEquals(model.d, externalModel.getD().toString());
...
assertEquals(model.o, externalModel.getO().toString());
assertNumberOfAssertionsInThisTest(15);
would not help you. Guess what: when pulling together my faked example, I omitted property 14 (model.n), but instead I had a copy/paste error and checked model.c two times, leading to an overall count of 15.
Therefore I agree with user Phil, just suggesting yet another approach, like this:
ensure that the bean classes have reasonable equals() (and maybe hashCode() methods). Either by using Lombok, or by having a base bean class that makes use of an EqualsBuilder (we actually do the later in our projects)
then have test code either use a faked bean and simply compare if that faked bean is equal to the bean that your production code created from a (maybe faked) external model object.

how to design if some constants are used by multiple classes

I've few common constants which are used by multiple classes.
What's the most effective way to design in this case:
Should I redefine the constants in each class?
Or should I separate such constants in a public class, and use the constants (in separate class) within each class?
Or is there any other better approach?
Note:- I'm looking for best OO technique which would be applicable for this.

Constants should be strictly related to some type, they shouldn't just "exist". A Constants class may seem convenient, but it will soon become unmaintainable, not to mention many consider it an antipattern.
It's hard to suggest improvements without seeing your code, but it seems like you need to rethink your design if you find yourself needing the same constants defined in a few different classes outside of the scope of a type.

Providing a Constant Util class is the cleanest way.
class ConstantUtil {
public static final int MAX_SIZE = 1<<10;
}
The typical folder heirarchy is like this
com.example.util.ConstantUtil

If the contants are dedicated to an api define them there. E.g.
public interface TaskService {
public static final int PRIORITY_LOW = -1;
public static final int PRIORITY_NORMAL = 0;
public static final int PRIORITY_HIGH = 1;
public void schedule(Task task, int priority);
}
If constants are not releated to a single api define a constants interface. E.g. javax.swing.WindowConstants.
Or is there any other better approach? Note:- I'm looking for best OO technique which would be applicable for this.
java
This brings us back to the question how constants are used. Most times they are used to write conditional code. E.g.
public class TaskServiceImpl implements TaskService {
private List<Task> lowPriority = new ArrayList<Task>();
private List<Task> normalPriority = new ArrayList<Task>();
private List<Task> highPriority = new ArrayList<Task>();
public void schedule(Task task, int priority){
if(priority == PRIORITY_HIGH ){
highPriority.add(task);
} else if(priority == PRIORITY_LOW ){
lowPriority.add(task);
} else if(priority == PRIORITY_NORMAL){
normalPriority.add(task);
} else {
....
}
}
}
In this case find out what the purpose of the constants is. In the example above the purpose is to group the tasks or if you think further to order them for execution. Move that logic to an own class. E.g. Introduce a Priority class that might implement Compareable ;)
You can also take a look at my blog about type-switches https://www.link-intersystems.com/blog/2015/12/03/enums-as-type-discriminator-anti-pattern/.
It is about enum misuse, but it also applies to constants.

You can try to create a class which contains all the constants(i.e, the second approach).
For example:
classname : MyConstantsClass.java
public static final String SOME_CONSTANT="value";
and then use it like
MyConstantsClass.SOME_CONSTANT
As some have suggested to use interface to create constants then I don't think that it would be a good choice. As using interface to create constants have certain disadvantages as well:
The usage of an interface does not allow to implement a mechanism for converting the constants to a visible/human readable
representation.
If the constants are an "implementation detail", an interface might not be the natural place for the value (CodeSmells, ListenToTheCode).
Due to Java compiler optimization, complete code recompilation of all classes using the constants is necessary if a constant changes.
Just changing the interface and recompiling it does not work (this
is, however the case with all constants defined as 'static final')
Please refer:
Interfaces For Defining Constants
Interface for constants
Class for constants

Constant class :
interface Constants {
int CONSTANT_ONE = 0;
int CONSTANT_TWO = 1;
int CONSTANT_THREE = 2;
String BASE_PATH = "YourPath";
}
And usage:
if (someValue == Constants.CONSTANT_ONE) {
}
Edit:
In most cases use interface instead of class if there is no need to implement this interface by some class, then it is no need to add this public static final, because by default it is public static final so your code looks more clean.

Design a class like AppUtil.java and and define your constants public static final like below:
public class AppUtil
{
public static final String IMAGE_STATUS="0";
}
and when you want to use variable use . like below:
AppUtil.IMAGE_STATUS

How to organize java 8 code with Functional interfaces

I have recently started reading about java 8 features and i am confused with what seems like a very basic thing. How to organize code in 'Functional style' ?
Whatever i do, it looks very object oriented to me.
Best to explain what i ask with an example.
#FunctionalInterface
public interface SubstringOperator {
String splitAtLastOccurence(String plainText, String delimiter);
}
Let's say that in certain class i always need exactly one specific implementation of the SubstringOperator interface. I could provide implementation in the constructor like below:
public class SomeClass {
private SubstringOperator substringOperator;
public SomeClass() {
substringOperator = (s, d) -> { return s.substring(s.lastIndexOf(d)+1);};
}
}
I could now use this implementation in any method within SomeClass like this:
//...
String valueAfterSplit = substringOperator.splitAtLastOccurence(plainText, "=");
If i now wish to add another class which reuses that specific SubstringOperator implementation, should i create another class which exposes the implementation via getters?
Am i missing something obvious, or:
functions must be contained in classes in order to reuse them ?
How is that any different than object oriented paradigm ?
Put aside Stream API and other thingies, i would like to get basic understanding about code organization in java 8 for Functional style programming.

Usually it's better to reuse existing functional interfaces instead of creating new ones. In your case the BinaryOperator<String> is what you need. And it's better to name the variables by their meaning, not by their type. Thus you may have:
public class SomeClass {
private BinaryOperator<String> splitAtLastOccurence =
(s, d) -> s.substring(s.lastIndexOf(d)+1);
}
Note that you can simplify single-statement lambda removing the return keyword and curly brackets. It can be applied like this:
String valueAfterSplit = splitAtLastOccurence.apply(plainText, "=");
Usually if your class uses the same function always, you don't need to store it in the variable. Use plain old method instead:
protected static String splitAtLastOccurence(String s, String d) {
return s.substring(s.lastIndexOf(d)+1);
}
And just call it:
String valueAfterSplit = splitAtLastOccurence(plainText, "=");
Functions are good when another class or method is parameterized by function, so it can be used with different functions. For example, you are writing some generic code which can process list of strings with additional other string:
void processList(List<String> list, String other, BinaryOperator<String> op) {
for(int i=0; i<list.size(); i++) {
list.set(i, op.apply(list.get(i), other));
}
}
Or more in java-8 style:
void processList(List<String> list, String other, BinaryOperator<String> op) {
list.replaceAll(s -> op.apply(s, other));
}
In this way you can use this method with different functions. If you already have splitAtLastOccurence static method defined as above, you can reuse it using a method reference:
processList(myList, "=", MyClass::splitAtLastOccurence);

How to implement interfaces with homographic methods in Java?

In English, a homograph pair is two words that have the same spelling but different meanings.
In software engineering, a pair of homographic methods is two methods with the same name but different requirements. Let's see a contrived example to make the question as clear as possible:
interface I1 {
/** return 1 */
int f()
}
interface I2 {
/** return 2*/
int f()
}
interface I12 extends I1, I2 {}
How can I implement I12? C# has a way to do this, but Java doesn't. So the only way around is a hack. How can it be done with reflection/bytecode tricks/etc most reliably (i.e it doesn't have to be a perfect solution, I just want the one that works the best)?
Note that some existing closed source massive piece of legacy code which I cannot legally reverse engineer requires a parameter of type I12 and delegates the I12 both to code that has I1 as a parameter, and code that has I2 as a parameter. So basically I need to make an instance of I12 that knows when it should act as I1 and when it should act as I2, which I believe can be done by looking at the bytecode at runtime of the immediate caller. We can assume that no reflection is used by the callers, because this is straightforward code. The problem is that the author of I12 didn't expect that Java merges f from both interfaces, so now I have to come up with the best hack around the problem. Nothing calls I12.f (obviously if the author wrote some code that actually calls I12.f, he would have noticed the problem before selling it).
Note that I'm actually looking for an answer to this question, not how to restructure the code that I can't change. I'm looking for the best heuristic possible or an exact solution if one exists. See Gray's answer for a valid example (I'm sure there are more robust solutions).
Here is a concrete example of how the problem of homographic methods within two interfaces can happen. And here is another concrete example:
I have the following 6 simple classes/interfaces. It resembles a business around a theater and the artists who perform in it. For simplicity and to be specific, let's assume they are all created by different people.
Set represents a set, as in set theory:
interface Set {
/** Complements this set,
i.e: all elements in the set are removed,
and all other elements in the universe are added. */
public void complement();
/** Remove an arbitrary element from the set */
public void remove();
public boolean empty();
}
HRDepartment uses Set to represent employees. It uses a sophisticated process to decode which employees to hire/fire:
import java.util.Random;
class HRDepartment {
private Random random = new Random();
private Set employees;
public HRDepartment(Set employees) {
this.employees = employees;
}
public void doHiringAndLayingoffProcess() {
if (random.nextBoolean())
employees.complement();
else
employees.remove();
if (employees.empty())
employees.complement();
}
}
The universe of a Set of employees would probably be the employees who have applied to the employer. So when complement is called on that set, all the existing employees are fired, and all the other ones that applied previously are hired.
Artist represents an artist, such as a musician or an actor. An artist has an ego. This ego can increase when others compliment him:
interface Artist {
/** Complements the artist. Increases ego. */
public void complement();
public int getEgo();
}
Theater makes an Artist perform, which possibly causes the Artist to be complemented. The theater's audience can judge the artist between performances. The higher the ego of the performer, the more likely the audience will like the Artist, but if the ego goes beyond a certain point, the artist will be viewed negatively by the audience:
import java.util.Random;
public class Theater {
private Artist artist;
private Random random = new Random();
public Theater(Artist artist) {
this.artist = artist;
}
public void perform() {
if (random.nextBoolean())
artist.complement();
}
public boolean judge() {
int ego = artist.getEgo();
if (ego > 10)
return false;
return (ego - random.nextInt(15) > 0);
}
}
ArtistSet is simply an Artist and a Set:
/** A set of associated artists, e.g: a band. */
interface ArtistSet extends Set, Artist {
}
TheaterManager runs the show. If the theater's audience judges the artist negatively, the theater talks to the HR department, which will in turn fire artists, hire new ones, etc:
class TheaterManager {
private Theater theater;
private HRDepartment hr;
public TheaterManager(ArtistSet artists) {
this.theater = new Theater(artists);
this.hr = new HRDepartment(artists);
}
public void runShow() {
theater.perform();
if (!theater.judge()) {
hr.doHiringAndLayingoffProcess();
}
}
}
The problem becomes clear once you try to implement an ArtistSet: both superinterfaces specify that complement should do something else, so you have to implement two complement methods with the same signature within the same class, somehow. Artist.complement is a homograph of Set.complement.

New idea, kinda messy...
public class MyArtistSet implements ArtistSet {
public void complement() {
StackTraceElement[] stackTraceElements = Thread.currentThread().getStackTrace();
// the last element in stackTraceElements is the least recent method invocation
// so we want the one near the top, probably index 1, but you might have to play
// with it to figure it out: could do something like this
boolean callCameFromHR = false;
boolean callCameFromTheatre = false;
for(int i = 0; i < 3; i++) {
if(stackTraceElements[i].getClassName().contains("Theatre")) {
callCameFromTheatre = true;
}
if(stackTraceElements[i].getClassName().contains("HRDepartment")) {
callCameFromHR = true;
}
}
if(callCameFromHR && callCameFromTheatre) {
// problem
}
else if(callCameFromHR) {
// respond one way
}
else if(callCameFromTheatre) {
// respond another way
}
else {
// it didn't come from either
}
}
}

Despite Gray Kemmey's valiant attempt, I would say the problem as you have stated it is not solvable. As a general rule given an ArtistSet you cannot know whether the code calling it was expecting an Artist or a Set.
Furthermore, even if you could, according to your comments on various other answers, you actually have a requirement to pass an ArtistSet to a vendor-supplied function, meaning that function has not given the compiler or humans any clue as to what it is expecting. You are completely out of luck for any sort of technically correct answer.
As practical programming matter for getting the job done, I would do the following (in this order):
File a bug report with whoever created an interface requiring ArtistSet and whoever generated the ArtistSet interface itself.
File a support request with the vendor supplying the function requiring an ArtistSet and ask them what they expect the behavior of complement() to be.
Implement the complement() function to throw an exception.
public class Sybil implements ArtistSet {
public void complement() {
throw new UnsupportedOperationException('What am I supposed to do');
}
...
}
Because seriously, you don't know what to do. What would be the correct thing to do when called like this (and how do you know for sure)?
class TalentAgent {
public void pr(ArtistSet artistsSet) {
artistSet.complement();
}
}
By throwing an exception you have a chance at getting a stack trace that gives you a clue as to which of the two behaviors the caller is expecting. With luck nobody calls that function, which is why the vendor got as far as shipping code with this problem. With less luck but still some, they handle the exception. If not even that, well, at least now you will have a stack trace you can review to decide what the caller was really expecting and possibly implement that (though I shudder to think of perpetuation a bug that way, I've explained how I would do it in this other answer).
BTW, for the rest of the implementation I would delegate everything to actual Artist and Set objects passed in via the constructor so this can be easily pulled apart later.

How to Solve For Your Specific Case
ArtistSet is simply an Artist and a Set:
/** A set of associated artists, e.g: a band. */
interface ArtistSet extends Set, Artist { }
From an OO perspective, that's not a useful declaration. An Artist is a type of noun, a "thing" that has defined properties and actions (methods).
A Set is an aggregate of things - a collection of unique elements. Instead, try:
ArtistSet is simply a Set of Artists.
/** A set of associated artists, e.g: a band. */
interface ArtistSet extends Set<Artist> { };
Then, for your particular case, the homonym methods are on interfaces that are never combined within the one type, so you have no clash and can program away...
Further, you don't need to declare ArtistSet because you aren't actually extending Set with any new declarations. You're just instantiating a type parameter, so you can replace all usage with Set<Artist>.
How to Solve For the More General Case
For this clash the method names don't even need to be homographic in the english language sense - they can be the same word with same english meaning, used in different contexts in java. Clash occurs if you have two interfaces that you wish to apply to a type but they contain the same declaration (e.g. method signature) with conflicting semantic/processing definitions.
Java does not allow you to implement the behaviour you request - you must have an alternative work-around. Java doesn't allow a class to provide multiple implementations for the same method signature from multiple different interfaces (implementing the same method multiple times with some form of qualification/alias/annotation to distinguish). See Java overriding two interfaces, clash of method names,
Java - Method name collision in interface implementation
Avoid use of Inheritence (extends or implements) and instead use Object Composition (see http://en.wikipedia.org/wiki/Composition_over_inheritance)
E.g. If you have the following
interface TV {
void switchOn();
void switchOff();
void changeChannel(int ChannelNumber);
}
interface Video {
void switchOn();
void switchOff();
void eject();
void play();
void stop();
}
Then if you have an object that is both of these things, you can combine the two in a new interface (optional) or type:
interface TVVideo {
TV getTv();
Video getVideo();
}
class TVVideoImpl implements TVVideo {
TV tv;
Video video;
public TVVideoImpl() {
tv = new SomeTVImpl(....);
video = new SomeVideoImpl(....);
}
TV getTv() { return tv };
Video getVideo() { return video };
}

How can I implement a class which has two superinterfaces having homographic methods?
In Java, a class which has two superinterfaces having homographic methods is considered to have only one implementation of this method. (See the Java Language Specification section 8.4.8). This allows classes to conveniently inherit from multiple interfaces that all implement the same other interface and only implement the function once. This also simplifies the language because this eliminates the need for syntax and method dispatching support for distinguishing between homographic methods based on which interface they came from.
So the correct way to implement a class which has two superinterfaces having homographic methods is to provide a single method that satisfies the contracts of both superinterfaces.
C# has a way to do this. How can it be done in Java? Is there no construct for this?
C# defines interfaces differently than Java does and therefore has capabilities that Java does not.
In Java, the language construct is defined to mean that all interfaces get the same single implementation of homographic methods. There is no Java language construct for creating alternate behaviors of multiply-inherited interface functions based on the compile time class of the object. This was a conscious choice made by the Java language designers.
If not, how can it be done with reflection/bytecode tricks/etc most reliably?
"It" cannot be done with reflection/bytecode tricks because the information needed to decide which interface's version of the homographic method to choose is not necessarily present in the Java source code. Given:
interface I1 {
// return ASCII character code of first character of String s
int f(String s); // f("Hello") returns 72
}
interface I2 {
// return number of characters in String s
int f(String s); // f("Hello") returns 5
}
interface I12 extends I1, I2 {}
public class C {
public static int f1(I1 i, String s) { return i.f(s); } // f1( i, "Hi") == 72
public static int f2(I2 i, String s) { return i.f(s); } // f2( i, "Hi") == 2
public static int f12(I12 i, String s) { return i.f(s);} // f12(i, "Hi") == ???
}
According to the Java language specification, a class implementing I12 must do so in such a way that C.f1(), C.f2(), and C.f12() return the exact same result when called with the same arguments. If C.f12(i, "Hello") sometimes returned 72 and sometimes returned 5 based on how C.f12() were called, that would be a serious bug in the program and a violation of the language specification.
Furthermore, if the author of class C expected some kind of consistent behavior out of f12(), there is no bytecode or other information in class C that indicates whether it should be the behavior of I1.f(s) or I2.f(s). If the author of C.f12() had in mind C.f("Hello") should return 5 or 72, there's no way to tell from looking at the code.
Fine, so I cannot in general provide different behaviors for homographic functions using bytecode tricks, but I really have a class like my example class TheaterManager. What should I do to implement ArtistSet.complement()?
The actual answer to the actual question you asked is to create your own substitute implementation of TheaterManager that does not require an ArtistSet. You do not need to change the library's implementation, you need to write your own.
The actual answer to the other example question you cite is basically "delegate I12.f() to I2.f()" because no function that receives an I12 object goes on to pass that object to a function expecting an I1 object.
Stack Overflow is only for questions and answers of general interest
One of the stated reasons to reject a question here is that "it is only relevant to an extraordinarily narrow situation that is not generally applicable to the worldwide audience of the internet." Because we want to be helpful, the preferred way to handle such narrow questions is to revise the question to be more broadly applicable. For this question I have taken the approach of answering the broadly applicable version of the question rather than actually editing the question to remove what makes it unique to your situation.
In the real world of commercial programming any Java library that has a broken interface like I12 would not accumulate even dozens of commercial clients unless it could be used by implementing I12.f() in one of these ways:
delegate to I1.f()
delegate to I2.f()
do nothing
throw an exception
pick one of the above strategies on a per-call basis based on the values of some members of the I12 object
If thousands or even only a handful of companies are using this part of this library in Java then you can be assured they have used one of those solutions. If the library is not in use by even a handful of companies then the question is too narrow for Stack Overflow.
OK, TheaterManager was an oversimplification. In the real case it is too hard for me to replace that class and I don't like any of the practical solutions you've outlined. Can't I just fix this with fancy JVM tricks?
It depends on what you want to fix. If you want to fix your specific library by mapping all the calls to I12.f() and then parsing the the stack to determine the caller and choosing a behavior based on that. You can access the stack via Thread.currentThread().getStackTrace().
If you run across a caller you do not recognize you may have a hard time figuring out which version they want. For example you may be called from a generic (as was the actual case in the other specific example you gave), like:
public class TalentAgent<T extends Artist> {
public static void butterUp(List<T> people) {
for (T a: people) {
a.complement()
}
}
}
In Java, generics are implemented as erasures, meaning all type information is thrown away at compile time. There is no class or method signature difference between a TalentAgent<Artist> and a TalentAgent<Set> and the formal type of the people parameter is just List. There is nothing in the class interface or method signature of the caller to tell you what to do by looking at the stack.
So you would need to implement multiple strategies, one of which would be decompiling the code of the calling method looking for clues that the caller is expecting one class or another. It would have to be very sophisticated to cover all the ways this could happen, because among other things you have no way of knowing in advance what class it actually expecting, only that it is expecting a class that implements one of the interfaces.
There are mature and extremely sophisticated open source bytecode utilities, including one that automatically generates a proxy for a given class at runtime (written long before there was support for that in the Java language), so the fact that there isn't an open source utility for handling this case speaks volumes about the ratio of effort to usefulness in pursuing this approach.

Okay, after much research, I have another idea to fully accommodate the situation. Since you can't directly modify their code... you can force the modifications yourself.
DISCLAIMER: The example code below is very simplified. My intention is to show the general method of how this might be done, not to produce functioning source code to do it (since that's a project in itself).
The issue is that the methods are homographic. So to solve it, we can just rename the methods. Simple, right? We can use the Instrument package to achieve this. As you'll see in the linked documentation, it allows you to make an "agent" which can directly modify classes as they're loaded or re-modify them even if they've already been loaded.
Essentially, this requires you to make two classes:
An agent class which preprocesses and reloads classes; and,
A ClassFileTransformer implementation which specifies the changes you want to make.
The agent class must have either a premain() or agentmain() method defined, based on whether you want it to begin its processing as the JVM starts up or after it is already running. Examples of this are in the package documentation above. These methods give you access to an Instrumenation instance, which will allow you to register your ClassFileTransformer. So it might look something like this:
InterfaceFixAgent.java
public class InterfaceFixAgent {
public static void premain(String agentArgs, Instrumentation inst) {
//Register an ArtistTransformer
inst.addTransformer(new ArtistTransformer());
//In case the Artist interface or its subclasses
//have already been loaded by the JVM
try {
for(Class<?> clazz : inst.getAllLoadedClasses()) {
if(Artist.class.isAssignableFrom(clazz)) {
inst.retransformClasses(clazz);
}
}
}
catch(UnmodifiableClassException e) {
//TODO logging
e.printStackTrace();
}
}
}
ArtistTransformer.java
public class ArtistTransformer implements ClassFileTransformer {
private static final byte[] BYTES_TO_REPLACE = "complement".getBytes();
private static final byte[] BYTES_TO_INSERT = "compliment".getBytes();
#Override
public byte[] transform(ClassLoader loader, String className,
Class<?> classBeingRedefined, ProtectionDomain protectionDomain,
byte[] classfileBuffer) throws IllegalClassFormatException {
if(Artist.class.isAssignableFrom(classBeingRedefined)) {
//Loop through the classfileBuffer, find sequences of bytes
//which match BYTES_TO_REPLACE, replace with BYTES_TO_INSERT
}
else return classfileBuffer;
}
This is, of course, simplified. It will replace the word "complement" with "compliment" in any class which extends or implements Artist, so you will very likely need to further conditionalize it (for example, if Artist.class.isAssignableFrom(classBeingRedefined) && Set.class.isAssignableFrom(classBeingRedefined), you obviously don't want to replace every instance of "complement" with "compliment", as the "complement" for Set is perfectly legitimate).
So, now we've corrected the Artist interface and its implementations. The typo is gone, the methods have two different names, so there is no homography. This allows us to have two different implementations in our CommunityTheatre class now, each of which will properly implement/override the methods from the ArtistSet.
Unfortunately, we've now created another (possibly even bigger) issue. We've just broken all the previously-legitimate references to complement() from classes implementing Artist. To fix this, we will need to create another ClassFileTransformer which replaces these calls with our new method name.
This is somewhat more difficult, but not impossible. Essentially, the new ClassFileTransformer (let's say we call it the OldComplementTransformer) will have to perform the following steps:
Find the same string of bytes as before (the one representing the old method name, "complement");
Get the bytes before this which represent the object reference calling the method;
Convert those bytes into an Object;
Check to see if that Object is an Artist; and,
If so, replace those bytes with the new method name.
Once you've made this second transformer, you can modify the InterfaceFixAgent to accommodate it. (I also simplified the retransformClasses() call, since in the example above we perform the needed check within the transformer itself.)
InterfaceFixAgent.java (modified)
public class InterfaceFixAgent {
public static void premain(String agentArgs, Instrumentation inst) {
//Register our transformers
inst.addTransformer(new ArtistTransformer());
inst.addTransformer(new OldComplementTransformer());
//Retransform the classes that have already been loaded
try {
inst.retransformClasses(inst.getAllLoadedClasses());
}
catch(UnmodifiableClassException e) {
//TODO logging
e.printStackTrace();
}
}
}
And now... our program is good to go. It certainly wouldn't be easy to code, and it will be utter hell to QA and test. But it's certainly robust, and it solves the issue. (Technically, I suppose it avoids the issue by removing it, but... I'll take what I can get.)
Other ways we might have solved the problem:
The Unsafe API
A native method written in C
Both of these would allow you to directly manipulate bytes in memory. A solution could certainly be designed around these, but I believe it would be much more difficult and much less safe. So I went with the route above.
I think this solution could even be made more generic into an incredibly useful library for integrating code bases. Specify which interface and which method you need refactored in a variable, a command line argument, or a configuration file, and let her loose. The library that reconciles conflicting interfaces in Java at runtime. (Of course, I think it would still be better for everyone if they just fixed the bug in Java 8.)

Here's what I'd do to remove the ambiguity:
interface Artist {
void complement(); // [SIC] from OP, really "compliment"
int getEgo();
}
interface Set {
void complement(); // as in Set Theory
void remove();
boolean empty(); // [SIC] from OP, I prefer: isEmpty()
}
/**
* This class is to represent a Set of Artists (as a group) -OR-
* act like a single Artist (with some aggregate behavior). I
* choose to implement NEITHER interface so that a caller is
* forced to designate, for any given operation, which type's
* behavior is desired.
*/
class GroupOfArtists { // does NOT implement either
private final Set setBehavior = new Set() {
#Override public void remove() { /*...*/ }
#Override public boolean empty() { return true; /* TODO */ }
#Override public void complement() {
// implement Set-specific behavior
}
};
private final Artist artistBehavior = new Artist() {
#Override public int getEgo() { return Integer.MAX_VALUE; /* TODO */ }
#Override public void complement() {
// implement Artist-specific behavior
}
};
Set asSet() {
return setBehavior;
}
Artist asArtist() {
return artistBehavior;
}
}
If I were passing this object to the HR department, I'd actually give it the value returned from asSet() to hire/fire the entire group.
If I were passing this object to the Theater for a performance, I'd actually give it the value returned from asArtist() to be treated as talent.
This works as long as YOU are in control of talking to the different components directly...
But I realize that your problem is a single third-party vendor has created a component, TheaterManager, that expects one object for both of these functions and it won't know about the asSet and asArtist methods. The problem is not with the vendors that created Set and Artist, it is the vendor that combined them instead of using a Visitor pattern or just specifying an interface that would mirror the asSet and asArtist methods I made above. If you can convince your one vendor "C" to fix that interface, your world will be a lot happier.
Good luck!

Dog, I have a strong feeling you are leaving out some details that are crucial to the solution. This often happens on SO because
people need to leave out a lot of details to get the question to a reasonable size and scope,
people do not fully understand the problem and the solution (which is why they are asking for help) so they cannot be sure which details are important and which are not, and
the reason the person cannot solve the problem on their own is because they do not understand the importance of this detail, which is the same reason they left it out.
I've said in another answer what I would do about ArtistSet. But keeping the above in mind I will give you another solution to a slightly different problem. Lets say I had code from a bad vendor:
package com.bad;
public interface IAlpha {
public String getName();
// Sort Alphabetically by Name
public int compareTo(IAlpha other);
}
This is bad because you should declare a function returning a Comparator<IAlpha> to implement the sorting strategy, but whatever. Now I get code from a worse company:
package com.worse;
import com.bad.IAlpha;
// an Alpha ordered by name length
public interface ISybil extends IAlpha, Comparable<IAlpha> {}
This is worse, because it is totally wrong, in that it overrides behavior incompatibly. An ISybil orders itself by name length, but an IAlpha orders itself alphabetically, except an ISybil is an IAlpha. They were mislead by the anti-pattern of IAlpha when they could and should have done something like:
public interface ISybil extends IAlpha {
public Comparator<IAlpha> getLengthComparator();
}
However, this situation is still much better than ArtistSet because here the expected behavior is documented. There is no confusion about what ISybil.compareTo() should do. So I would create classes as follows. A Sybil class that implements compareTo() as com.worse expects and delegates everything else:
package com.hack;
import com.bad.IAlpha;
import com.worse.ISybil;
public class Sybil implements ISybil {
private final Alpha delegate;
public Sybil(Alpha delegate) { this.delegate = delegate; }
public Alpha getAlpha() { return delegate; }
public String getName() { return delegate.getName(); }
public int compareTo(IAlpha other) {
return delegate.getName().length() - other.getName().length();
}
}
and an Alpha class that works exactly like com.bad said it should:
package com.hack;
import com.bad.IAlpha;
public class Alpha implements IAlpha {
private String name;
private final Sybil sybil;
public Alpha(String name) {
this.name = name;
this.sybil = new Sybil(this);
}
// Sort Alphabetically
public int compareTo(IAlpha other) {
return name.compareTo(other.getName());
}
public String getName() { return name; }
public Sybil getSybil() { return sybil; }
}
Note that I included type conversion methods: Alpha.getSybil() and Sybil.getAlpha(). This is so I could create my own wrappers around any com.worse vendor's methods that take or return Sybils so I can avoid polluting my code or any other vendor's code with com.worse's breakage. So if com.worse had:
public ISybil breakage(ISybil broken);
I could write a function
public Alpha safeDelegateBreakage(Alpha alpha) {
return breakage(alpha.getSybil).getAlpha();
}
and be done with it, except I would still complain vociferously to com.worse and politely to com.bad.

Extending String for Typesafety - Java

I am considering a design in Java where I want a string object but with more 'type-safety' than just being of class String. This because I have a number of 'POJO' objects for Hibernate, representing my database tables. Each of these classes has a large number of public static fields representing the properties of the class, I.e.:
public class PersistantBean {
public static String PROP_FIELD_COLUMN_ONE="columnOne";
public static String PROP_FIELD_COLUMN_TWO="columnTwo";
// [...]
These properties are used when we need to access a property in a generic way, e.g. for code I am currently writing .parseAndSet(PROP_FIELD_PRICE,"£3.00").
I would like to be able to add a stronger type to the PROP_FIELD_... fields so that I could write
public class PersistantBean {
public static PropertyName PROP_FIELD_COLUMN_ONE="columnOne";
public static PropertyName PROP_FIELD_COLUMN_TWO="columnTwo";
// [...]
with minimal changes to other parts of the project,
so that parseAndSet would look like:
public void parseAndSet(PropertyName prop, String priceToParse)
Essentially, I would like PropertyName to be a type that is like String in everyway apart from the compiler would error if I tried to put a String where a PropertyName was expected, is any design pattern like this possible.
(I am shying away from Enums, although now I mention it, Enums may be the way to go.)

For Java 1.5 and above, just use an enum type.
For Java 1.4 and below, use the typesafe enum pattern. E.g.
public class Suit {
private final String name;
public static final Suit CLUBS =new Suit("clubs");
public static final Suit DIAMONDS =new Suit("diamonds");
public static final Suit HEARTS =new Suit("hearts");
public static final Suit SPADES =new Suit("spades");
private Suit(String name){
this.name =name;
}
public String toString(){
return name;
}
}

enum(enumeration) is a better idea, which above mentioned scenario.
eg:
enum PROP_FIELD_COLUMN {
columnOne, columnTwo,etc
}

I'd use an Enum. That way you get compile-time checking.
If your Strings really have a good fairly standard naming convention, like "column" + "One", "Two", etc. as in your example, you could save a lot of work by combining an enum for the prefix with an int for the suffix. So, create a class or utility method that takes an enum for the prefix, e.g. COLUMN, and combines it with an int, say 2, to yield "columnTwo".
An alternative might be be for your code, like parseAndSet, to validate the passed in String against an array or Collection of legal Strings, or maybe a regex, and throw an IllegalArgumentException. You'd get runtime checking and if you have good unit tests this could work.
EDIT ADDED
#sethupathi.t had a nice idea in his answer - In some cases it may be preferable to make the 2nd argument (for which I used an int) also an enum.

As far as I can tell, there are two reasonable ways to do what you want to do.
The first way (and probably best way, if it works for you) is to use an enum, as mentioned in another answer.
The second way, which may be necessary if you do not know all of your PropertyName's at runtime, would be to use a PropertyNameFactory along the lines of:
public class PropertyNameFactory
{
public static PropertyName getPropertyName(String propertyName)
{
// Check validity of the propertyName against what ever rules we
// have defined (maybe valid propertyNames are read from a DB at
// startup, etc).
if (isValid(propertyName))
{
// Ideally get from a cache, but for the sake of the example
// we will create a new one...
return new PropertyName(propertyName);
}
throw new IllegalArgumentException("Invalid property name: " + propertyName);
}
}
This is not ideal in that it does not provide true type safety of your property names, but it does ensure their validity.

I have to second the Enum answers.
However, a more literal answer to your question is that Java provides an interface for String-like objects, java.lang.CharSequence, and many parts of the standard Java libraries have been updated to accept CharSequence where appropriate. This will not however give you the behavior that you want, which is to have your class behave as a subtype of String.