We Keep Coding

In Line interface, I must call close() for all instance, or only when Line is opened?

By the definition of AutoCloseable interface,
I must call close() for ALL instances.
i.e. I must write like this.
try(A a = new A()){
//do something
}
In java.sound.sampled.SourceDataLine interface,
or more commonly, in java.sound.sampled.Line interface,
is it required to call close() for ALL instances,
or I must call close() ONLY AFTER open() has called ?
If the official document explicitly states that I must close only when isOpened ,
I want to write like this.
but I couldn't find mention.
//can I write like this ?
SourceDataLine sdl;
try{
sdl = AudioSystem.getSourceDataLine(audioFormat);
sdl.open(audioFormat,bufferSize);
}catch(LineUnavailableException ex){
throw new RuntimeException(null,ex);
}
try(SourceDataLine sdlInTryWithResources = sdl){
//do something
}

Your actual question should be “does it harm to call close() when the data line has not been opened?” and the answer is “no”, so you can simply use
try(SourceDataLine sdl = AudioSystem.getSourceDataLine(audioFormat)) {
sdl.open(audioFormat, bufferSize);
// work with sdl
}
catch(LineUnavailableException ex) {
throw new RuntimeException(ex);
}
Note that javax.sound.sampled.Line has been deliberately changed in Java 7 to extend AutoCloseable, whose sole purpose is to allow the resource to be used within a try-with-resource statement.

It seems that you are overthinking things.
Just image try-with-resources would not exist and write down your code as you would have done prior Java 1.7.
For sure, you end up with something like:
Whatever somethingThatNeedsClosing = null;
try {
somethingThatNeedsClosing = ...
somethingThatNeedsClosing.whatever();
} catch (NoIdeaException e) {
error handling
} finally {
if (somethingThatNeedsClosing != null) {
somethingThatNeedsClosing.close()
}
}
Try-with-resources simply allows you to reduce this example accordingly.
In other words: try-with-resources allows you to define one (or more) resource(s) that will be used within the try block; and that will finally be closed. As in: each and any resource declared for try ... will be closed.
More specifically: don't think about other instances of your resource. Focus on the one that you are currently dealing with.

Is having a return statement just to satisfy syntax bad practice?

Consider the following code:
public Object getClone(Cloneable a) throws TotallyFooException {
if (a == null) {
throw new TotallyFooException();
}
else {
try {
return a.clone();
} catch (CloneNotSupportedException e) {
e.printStackTrace();
}
}
//cant be reached, in for syntax
return null;
}
The return null; is necessary since an exception may be caught, however in such a case since we already checked if it was null (and lets assume we know the class we are calling supports cloning) so we know the try statement will never fail.
Is it bad practice to put in the extra return statement at the end just to satisfy the syntax and avoid compile errors (with a comment explaining it will not be reached), or is there a better way to code something like this so that the extra return statement is unnecessary?

A clearer way without an extra return statement is as follows. I wouldn't catch CloneNotSupportedException either, but let it go to the caller.
if (a != null) {
try {
return a.clone();
} catch (CloneNotSupportedException e) {
e.printStackTrace();
}
}
throw new TotallyFooException();
It's almost always possible to fiddle with the order to end up with a more straight-forward syntax than what you initially have.

It definitely can be reached. Note that you're only printing the stacktrace in the catch clause.
In the scenario where a != null and there will be an exception, the return null will be reached. You can remove that statement and replace it with throw new TotallyFooException();.
In general*, if null is a valid result of a method (i.e. the user expects it and it means something) then returning it as a signal for "data not found" or exception happened is not a good idea. Otherwise, I don't see any problem why you shouldn't return null.
Take for example the Scanner#ioException method:
Returns the IOException last thrown by this Scanner's underlying Readable. This method returns null if no such exception exists.
In this case, the returned value null has a clear meaning, when I use the method I can be sure that I got null only because there was no such exception and not because the method tried to do something and it failed.
*Note that sometimes you do want to return null even when the meaning is ambiguous. For example the HashMap#get:
A return value of null does not necessarily indicate that the map contains no mapping for the key; it's also possible that the map explicitly maps the key to null. The containsKey operation may be used to distinguish these two cases.
In this case null can indicate that the value null was found and returned, or that the hashmap doesn't contain the requested key.

Is it bad practice to put in the extra return statement at the end just to satisfy the syntax and avoid compile errors (with a comment explaining it will not be reached)
I think return null is bad practice for the terminus of an unreachable branch. It is better to throw a RuntimeException (AssertionError would also be acceptable) as to get to that line something has gone very wrong and the application is in an unknown state.
Most like this is (like above) because the developer has missed something (Objects can be none-null and un-cloneable).
I'd likely not use InternalError unless I'm very very sure that the code is unreachable (for example after a System.exit()) as it is more likely that I make a mistake than the VM.
I'd only use a custom exception (such as TotallyFooException) if getting to that "unreachable line" means the same thing as anywhere else you throw that exception.

You caught the CloneNotSupportedException which means your code can handle it. But after you catch it, you have literally no idea what to do when you reach the end of the function, which implies that you couldn't handle it. So you're right that it is a code smell in this case, and in my view means you should not have caught CloneNotSupportedException.

I would prefer to use Objects.requireNonNull() to check if the Parameter a is not null. So it's clear when you read the code that the parameter should not be null.
And to avoid checked Exceptions I would re throw the CloneNotSupportedException as a RuntimeException.
For both you could add nice text with the intention why this shouldn't happen or be the case.
public Object getClone(Object a) {
Objects.requireNonNull(a);
try {
return a.clone();
} catch (CloneNotSupportedException e) {
throw new IllegalArgumentException(e);
}
}

The examples above are valid and very Java. However, here's how I would address the OP's question on how to handle that return:
public Object getClone(Cloneable a) throws CloneNotSupportedException {
return a.clone();
}
There's no benefit for checking a to see if it is null. It's going to NPE. Printing a stack trace is also not helpful. The stack trace is the same regardless of where it is handled.
There is no benefit to junking up the code with unhelpful null tests and unhelpful exception handling. By removing the junk, the return issue is moot.
(Note that the OP included a bug in the exception handling; this is why the return was needed. The OP would not have gotten wrong the method I propose.)

In this sort of situation I would write
public Object getClone(SomeInterface a) throws TotallyFooException {
// Precondition: "a" should be null or should have a someMethod method that
// does not throw a SomeException.
if (a == null) {
throw new TotallyFooException() ; }
else {
try {
return a.someMethod(); }
catch (SomeException e) {
throw new IllegalArgumentException(e) ; } }
}
Interestingly you say that the "try statement will never fail", but you still took the trouble to write a statement e.printStackTrace(); that you claim will never be executed. Why?
Perhaps your belief is not that firmly held. That is good (in my opinion), since your belief is not based on the code you wrote, but rather on the expectation that your client will not violate the precondition. Better to program public methods defensively.
By the way, your code won't compile for me. You can't call a.clone() even if the type of a is Cloneable. At least Eclipse's compiler says so. Expression a.clone() gives error
The method clone() is undefined for the type Cloneable
What I would do for your specific case is
public Object getClone(PubliclyCloneable a) throws TotallyFooException {
if (a == null) {
throw new TotallyFooException(); }
else {
return a.clone(); }
}
Where PubliclyCloneable is defined by
interface PubliclyCloneable {
public Object clone() ;
}
Or, if you absolutely need the parameter type to be Cloneable, the following at least compiles.
public static Object getClone(Cloneable a) throws TotallyFooException {
// Precondition: "a" should be null or point to an object that can be cloned without
// throwing any checked exception.
if (a == null) {
throw new TotallyFooException(); }
else {
try {
return a.getClass().getMethod("clone").invoke(a) ; }
catch( IllegalAccessException e ) {
throw new AssertionError(null, e) ; }
catch( InvocationTargetException e ) {
Throwable t = e.getTargetException() ;
if( t instanceof Error ) {
// Unchecked exceptions are bubbled
throw (Error) t ; }
else if( t instanceof RuntimeException ) {
// Unchecked exceptions are bubbled
throw (RuntimeException) t ; }
else {
// Checked exceptions indicate a precondition violation.
throw new IllegalArgumentException(t) ; } }
catch( NoSuchMethodException e ) {
throw new AssertionError(null, e) ; } }
}

Is having a return statement just to satisfy syntax bad practice?
As others have mentioned, in your case this does not actually apply.
To answer the question, though, Lint type programs sure haven't figured it out! I have seen two different ones fight it out over this in a switch statement.
switch (var)
{
case A:
break;
default:
return;
break; // Unreachable code. Coding standard violation?
}
One complained that not having the break was a coding standard violation. The other complained that having it was one because it was unreachable code.
I noticed this because two different programmers kept re-checking the code in with the break added then removed then added then removed, depending on which code analyzer they ran that day.
If you end up in this situation, pick one and comment the anomaly, which is the good form you showed yourself. That's the best and most important takeaway.

It isn't 'just to satisfy syntax'. It is a semantic requirement of the language that every code path leads to a return or a throw. This code doesn't comply. If the exception is caught a following return is required.
No 'bad practice' about it, or about satisfying the compiler in general.
In any case, whether syntax or semantic, you don't have any choice about it.

I would rewrite this to have the return at the end. Pseudocode:
if a == null throw ...
// else not needed, if this is reached, a is not null
Object b
try {
b = a.clone
}
catch ...
return b

No one mentioned this yet so here goes:
public static final Object ERROR_OBJECT = ...
//...
public Object getClone(Cloneable a) throws TotallyFooException {
Object ret;
if (a == null)
throw new TotallyFooException();
//no need for else here
try {
ret = a.clone();
} catch (CloneNotSupportedException e) {
e.printStackTrace();
//something went wrong! ERROR_OBJECT could also be null
ret = ERROR_OBJECT;
}
return ret;
}
I dislike return inside try blocks for that very reason.

The return null; is necessary since an exception may be caught,
however in such a case since we already checked if it was null (and
lets assume we know the class we are calling supports cloning) so we
know the try statement will never fail.
If you know details about the inputs involved in a way where you know the try statement can never fail, what is the point of having it? Avoid the try if you know for sure things are always going to succeed (though it is rare that you can be absolutely sure for the whole lifetime of your codebase).
In any case, the compiler unfortunately isn't a mind reader. It sees the function and its inputs, and given the information it has, it needs that return statement at the bottom as you have it.
Is it bad practice to put in the extra return statement at the end
just to satisfy the syntax and avoid compile errors (with a comment
explaining it will not be reached), or is there a better way to code
something like this so that the extra return statement is unnecessary?
Quite the opposite, I'd suggest it's good practice to avoid any compiler warnings, e.g., even if that costs another line of code. Don't worry too much about line count here. Establish the reliability of the function through testing and then move on. Just pretending you could omit the return statement, imagine coming back to that code a year later and then try to decide if that return statement at the bottom is going to cause more confusion than some comment detailing the minutia of why it was omitted because of assumptions you can make about the input parameters. Most likely the return statement is going to be easier to deal with.
That said, specifically about this part:
try {
return a.clone();
} catch (CloneNotSupportedException e) {
e.printStackTrace();
}
...
//cant be reached, in for syntax
return null;
I think there's something slightly odd with the exception-handling mindset here. You generally want to swallow exceptions at a site where you have something meaningful you can do in response.
You can think of try/catch as a transaction mechanism. try making these changes, if they fail and we branch into the catch block, do this (whatever is in the catch block) in response as part of the rollback and recovery process.
In this case, merely printing a stacktrace and then being forced to return null isn't exactly a transaction/recovery mindset. The code transfers the error-handling responsibility to all the code calling getClone to manually check for failures. You might prefer to catch the CloneNotSupportedException and translate it into another, more meaningful form of exception and throw that, but you don't want to simply swallow the exception and return a null in this case since this is not like a transaction-recovery site.
You'll end up leaking the responsibilities to the callers to manually check and deal with failure that way, when throwing an exception would avoid this.
It's like if you load a file, that's the high-level transaction. You might have a try/catch there. During the process of trying to load a file, you might clone objects. If there's a failure anywhere in this high-level operation (loading the file), you typically want to throw exceptions all the way back to this top-level transaction try/catch block so that you can gracefully recover from a failure in loading a file (whether it's due to an error in cloning or anything else). So we generally don't want to just swallow up an exception in some granular place like this and then return a null, e.g., since that would defeat a lot of the value and purpose of exceptions. Instead we want to propagate exceptions all the way back to a site where we can meaningfully deal with it.

Your example is not ideal to illustrate your question as stated in the last paragraph:
Is it bad practice to put in the extra return statement at the end
just to satisfy the syntax and avoid compile errors (with a comment
explaining it will not be reached), or is there a better way to code
something like this so that the extra return statement is unnecessary?
A better example would be the implementation of clone itself:
public class A implements Cloneable {
public Object clone() {
try {
return super.clone() ;
} catch (CloneNotSupportedException e) {
throw new InternalError(e) ; // vm bug.
}
}
}
Here the catch clause should never be entered. Still the syntax either requires to throw something or return a value. Since returning something does not make sense, an InternalError is used to indicate a severe VM condition.

How to ignore Exceptions in Java

I have the following code:
TestClass test=new TestClass();
test.setSomething1(0); //could, but probably won't throw Exception
test.setSomething2(0); //could, but probably won't throw Exception
I would like to execute: test.setSomething2(0); even if test.setSomething(0) (the line above it) throws an exception. Is there a way to do this OTHER than:
try{
test.setSomething1(0);
}catch(Exception e){
//ignore
}
try{
test.setSomething2(0);
}catch(Exception e){
//ignore
}
I have a lot of test.setSomething's in a row and all of them could throw Exceptions. If they do, I just want to skip that line and move to the next one.
For clarification, I don't care if it throws an Exception, and I can't edit the source code of the code which throws this exception.
THIS IS A CASE WHERE I DON'T CARE ABOUT THE EXCEPTIONS (please don't use universally quantified statements like "you should never ignore Exceptions"). I am setting the values of some Object. When I present the values to a user, I do null checks anyway, so it doesn't actually matter if any of the lines of code execute.

try {
// Your code...
} catch (Exception ignore) { }
Use the word ignore after the Exception keyword.

There is no way to fundamentally ignore a thrown exception. The best that you can do is minimize the boilerplate you need to wrap the exception-throwing code in.
If you are on Java 8, you can use this:
public static void ignoringExc(RunnableExc r) {
try { r.run(); } catch (Exception e) { }
}
#FunctionalInterface public interface RunnableExc { void run() throws Exception; }
Then, and implying static imports, your code becomes
ignoringExc(() -> test.setSomething1(0));
ignoringExc(() -> test.setSomething2(0));

IntelliJ Idea IDE suggests to rename a variable to ignored
when it isn't used.
This is my sample code.
try {
messageText = rs.getString("msg");
errorCode = rs.getInt("error_code");
} catch (SQLException ignored) { }

Unfortunately no, there isn't, and this is by intention. When used correctly, exceptions should not be ignored as they indicate that something didn't work and that you probably shouldn't continue down your normal execution path. Completely ignoring exceptions is an example of the 'Sweep it under the rug' anti-pattern, which is why the language doesn't support doing so easily.
Perhaps you should look at why TestClass.setSomething is throwing exceptions. Is whatever you're trying to 'test' really going to be valid if a bunch of setter methods didn't work correctly?

You can't ignore exception in Java. If a method declares being able to throw something this is because something important can't be done, and the error can't be corrected by the method designer. So if you really wan't to simplify your life encapsulate the method call in some other method like this :
class MyExceptionFreeClass {
public static void setSomething1(TestClass t,int v) {
try {
t.setSomething1(v);
} catch (Exception e) {}
public static void setSomething2(TestClass t,int v) {
try {
t.setSomething2(v);
} catch (Exception e) {}
}
and call it when you need it:
TestClass test=new TestClass();
MyExceptionFreeClass.setSomething1(test,0);
MyExceptionFreeClass.setSomething2(test,0);

You should not ignore Exceptions. You should handle them. If you want to make your test code simple, then add the try-catch block into your functions. The greatest way to ignore exceptions is to prevent them by proper coding.

I know this is old, but I do think there are occasions when you want to ignore an exception. Consider you have a string that contains a delimited set of parts to be parsed. But, this string can sometimes contain say, 6 or 7 or 8 parts. I don't feel that checking the len each time in order to establish an element exists in the array is as straight forward as simply catching the exception and going on. For example, I have a string delimited by '/' character that I want to break apart:
public String processLine(String inLine) {
partsArray = inLine.split("/");
//For brevity, imagine lines here that initialize
//String elems[0-7] = "";
//Now, parts array may contains 6, 7, or 8 elements
//But if less than 8, will throw the exception
try {
elem0 = partsArray[0];
elem1 = partsArray[1];
elem2 = partsArray[2];
elem3 = partsArray[3];
elem4 = partsArray[4];
elem5 = partsArray[5];
elem6 = partsArray[6];
elem7 = partsArray[7];
catch (ArrayIndexOutOfBoundsException ignored) { }
//Just to complete the example, we'll append all the values
//and any values that didn't have parts will still be
//the value we initialized it to, in this case a space.
sb.append(elem0).append(elem1).append(elem2)...append(elem7);
//and return our string of 6, 7, or 8 parts
//And YES, obviously, this is returning pretty much
//the same string, minus the delimiter.
//You would likely do things to those elem values
//and then return the string in a more formatted way.
//But was just to put out an example where
//you really might want to ignore the exception
return sb.toString();
}

Those who write empty catch blocks shall burn in the Hell for the eternity.
Or worse, they will be forced to debug the damn rubbish they wrote forever and ever.
That said, one thing you might want to do is writing exception handling in a less verbose way. The NoException library is very good at that.

String inside dot operators

I'm pretty sure this is impossible (considering it is such abysmal programming practice), but I'm going to ask anyway.
In Java, is there a way to use a string in place of a method name (or something else) using the dot operator?
For example: java.stringname.NumericShaper(); where stringname = "awt.font"
I'm trying to put some repetitive code into an iterative loop. For example, one of my variables is "Settings.can1.baud", and I want to iterate the "can1" part each time I go through the loop. Perhaps there's a better way to do this?
I'm new to Java programming, so I'm not sure that made any sense...

If you mean you have a bunch of members called can1, can2, can3, etc., then you should use an array or a collection instead.
It is possible to do what you want using reflection. But it's fiddly, bad practice (often), and unnecessary in this case.

You could do this using reflection:
try {
//loop over stringnames?
String stringname = "awt.font";
Class<?> numericShaperClass = Class.forName("java." + stringname + ".NumericShaper");
NumericShaper numericShaper = (NumericShaper) numericShaperClass.newInstance();
} catch (ClassNotFoundException e) {
e.printStackTrace();
} catch (InstantiationException e) {
e.printStackTrace();
} catch (IllegalAccessException e) {
e.printStackTrace();
}
}
As for the second part of your question, you can access the member variables of your Properties class using the Class.getField() method.
Using reflection might be overkill in this situation and can result in some pretty unreadable, and possibly slow code.

Is it ok to handle a class metadata through reflection to ensure a DRY approach?

The title might seem unsettling, but let me explain.
I'm facing an interesting challenge, where I have a hierarchy of classes that have associated an object that stores metadata related to each one of its attributes (an int-valued enum with edit flags like UPDATED or NO_UPDATE).
The problem comes when merging two objects, because I dont want to check EVERY field on a class to see if it was updated and skip or apply the changes.
My idea: Reflection.
All the objects are behind an interface, so I could use IObject.class.getMethods() and iterate over that array in this fashion:
IClass class = //Instance of the first class;
IAnotherClass anotherClass = //Instance of the second class;
for(Method m : IObject.class.getMethods()) {
if(m.getName().startsWith("get")) {
try {
//Under this method (which is a getter) I cast it on
//both classes who implement interfaces that extend an
//interface that defines the getters to make them
//consistent and ensure I'll invoke the same methods.
String propertyClass = (String)m.invoke(class);
String propertyAnotherClass = (String)m.invoke(anotherClass);
if(propertyClass != propertyAnotherClass) {
//Update attribute and attribute status.
}
} catch (Exception e) {
}
}
}
Is there another way to implement this or should I stick to lengthy methods invoking attribute per attribute and doing the checks like that?. The objects are not going to change that much and the architecture is quite modular, so there is not much update involved if the fields change but having to change a method like that worries me a little.
EDIT 1: I'm posting a working code of what I have got so far. This code is a solution for me but, tough it works, I'm using it as a last resource not because I have time to spend but because I don't want to rediscover the wheel. If I use it, I'll make a static list with the methods so I only have to fetch that list once, considering the fact that AlexR pointed out.
private static void merge(IClazz from, IClazz to) {
Method methods[] = from.getClass().getDeclaredMethods();
for(Method m : methods) {
if(m.getName().startsWith("get") && !m.getName().equals("getMetadata")) {
try {
String commonMethodAnchor = m.getName().split("get")[1];
if(!m.getReturnType().cast(m.invoke(from)).equals(m.getReturnType().cast(m.invoke(to)))) {
String setterMethodName = "set" + commonMethodAnchor;
Method setter = IClazz.class.getDeclaredMethod(setterMethodName, m.getReturnType());
setter.invoke(to, m.getReturnType().cast(m.invoke(from)));
//Updating metadata
String metadataMethodName = "set" + commonMethodAnchor + "Status";
Method metadataUpdater = IClazzMetadata.class.getDeclaredMethod(metadataMethodName, int.class);
metadataUpdater.invoke(to.getMetadata(), 1);
}
} catch (Exception e) {
}
}
}
}
metadataUpdater sets the value to 1 just to simulate the "UPDATED" flag I'm using on the real case scenario.
EDIT 3: Thanks Juan, David and AlexR for your suggestions and directions! They really pointed me to consider things I did not consider at first (I'm upvoting all your answers because all of them helped me).
After adding what AlexR sugegsted and checking jDTO and Apache Commons (finding out that in the end the general concepts are quite similar) I've decided to stick to my code instead of using other tools, since it is working given the object hierarchy and metadata structure of the solution and there are no exceptions popping up so far. The code is the one on the 2nd edit and I've placed it on a helper class that did the trick in the end.

Apache Commons Bean Utils may resolve your problem: http://commons.apache.org/beanutils/
If you want to copy all properties, try to use copyProperties: http://commons.apache.org/beanutils/v1.8.3/apidocs/src-html/org/apache/commons/beanutils/BeanUtils.html#line.134
Look an example from: http://www.avajava.com/tutorials/lessons/how-do-i-copy-properties-from-one-bean-to-another.html
FromBean fromBean = new FromBean("fromBean", "fromBeanAProp", "fromBeanBProp");
ToBean toBean = new ToBean("toBean", "toBeanBProp", "toBeanCProp");
System.out.println(ToStringBuilder.reflectionToString(fromBean));
System.out.println(ToStringBuilder.reflectionToString(toBean));
try {
System.out.println("Copying properties from fromBean to toBean");
BeanUtils.copyProperties(toBean, fromBean);
} catch (IllegalAccessException e) {
e.printStackTrace();
} catch (InvocationTargetException e) {
e.printStackTrace();
}
System.out.println(ToStringBuilder.reflectionToString(fromBean));
System.out.println(ToStringBuilder.reflectionToString(toBean));

I think the best approach would be using proxy objects, either dynamic proxies or cglib enhancers or something like it, so you decorate the getters and setters and you can keep track of the changes there.
Hope it helps.

Your approach is OK, but keep in mind that getMethod() is much slower than invoke(), so if your code is performance critical you will probably want to cache the Method objects.