I've done some research to know if there is an equivalent to PHP die in java
Sometimes I'm doing small tests and I really want to stop my code at specific line , and return doesnt stop the code like "die" in php
Is there a die quivalent in java?
Use System.exit(0); to exit the java code.
Keep a note this will stop the JVM instance which is currently running.
If you want to come out of a method use return or throw exception to showcase error condition.
try:
System.out.println(message);
System.exit(0);
Disclaimer: I'm not that familiar with Java, I have a basic working knowledge of it, but haven't done a huge amount of work with it.
I suppose you could just throw() an exception and not catch it, that should halt execution. Of course if you have an exception handler for exceptions that aren't caught locally you might have problems.
Most IDEs let you set breakpoints where execution will stop and you'll be able to examine the state of variables, look at the call stack and so on. Both Eclipse and Netbeans support this. It might be a better option.
EDIT: There is also System.exit() which will halt execution. I still think breakpoints are a better option though.
<% if(true)return; %> ok
Related
I am relatively new to Stackoverflow and Java, but I have a little experience in C. I liked the very clean way of C exiting the programs after a malfunction with the 'exit()' function.
I found a similar function System.exit() in Java, what differs from the C function and when should I use a 'System.exit()' best instead of a simple 'return' in Java like in a void main function?
System.exit() will terminate the jvm initilized for this program, where return; just returns the control from current method back to caller
Also See
when-should-we-call-system-exit-in-java ?
System.exit() will exit the program no matter who calls it or why. return in the main will exit the main() but not kill anything that called it. For simple programs, there is no difference. If you want to call your main from another function (that may be doing performance measurements or error handling) it matters a lot. Your third option is to throw an uncaught runtime exception. This will allow you to exit the program from deep within the call stack, allow any external code that is calling your main a programmatic way to intercept and handle the exit, and when exiting, give the user context of what went wrong and where (as opposed to an exit status like 2).
System.exit() may be handy when you're ready to terminate the program on condition of the user (i.e. a GUI application). return is used to return to the last point in the program's execution. The two are very different operations.
Does java has library exception class which means actually not an error, but good termination? I know I can make my own class or use null, but wish to know.
EDIT 1
I want to use exception object as an old fashion return code for a method, so I need something equivalent to ERROR_SUCCESS code in Win32 API.
Exceptions in Java are meant to be used for abnormal termination only. Using them to flag correct termination should be considered really bad practice.
You might use return values instead.
To directly answer your question: No. There is no standard Java exception that means "this is a normal termination".
If you wanted to, you could define a custom exception that meant this for your application.
However,
... using an exception for "normal control flow" goes against the strong recommendations of the Java designers, and a Java "Best Practice" rule that has pretty much universal acceptance. This is not to say you should NEVER do this. It is just that the cases where it is justifiable to do this are VERY RARE. (And you'd need to take special steps to avoid grossly inefficient code ... )
Anyway, the fact that it is (almost) always a terrible idea to use exceptions for normal flow control explains why a standard exception was never created. The Java designers clearly didn't want to appear to be encouraging this practice.
The closest thing to a "good termination" signal I can think of is not an exception, but a call to System.exit(int) with 0 as argument, to indicate to the operating system that the program ended successfully. From the javadocs:
Terminates the currently running Java Virtual Machine. The argument serves as a status code; by convention, a nonzero status code indicates abnormal termination. This method calls the exit method in class Runtime. This method never returns normally.
As has been pointed out, an exception is not to be used to inform of a "good termination", quite the contrary.
No. Exception means exceptional situation. You should structure your program flow so that exceptions are thrown only for exceptional situations, rather than on the normal flow.
So, if you want to return "success": return true or some enum Result.SUCCESS.
Exceptions are mean to denote that something went wrong. Different exceptions depict different items which went wrong and will thus cause the program to terminate if not handled. Something successfully finishing is not an exception.
I think what you need to do is to either return a particular value, or else, make your application fire some sort of event. In this case throwing exception is not (at least for me) recommended.
Depends what you define as "good termination" I guess - is a security exception good because it stopped someone from hacking your system? It's not really an error, but it is an abnormal situation that you need to handle.
In general exceptions are designed to be used for exceptional conditions only (which may or may not be an error in your code - it could mean that some resource is unavailable, or a security check failed etc.)
If you are using exceptions for regular control flow (i.e. they are getting thrown in normal, expected circumstances) then you are probably doing something wrong.
Maybe you mean an InterrupedException? This one is thrown, when you wish to terminate a thread gracefully.
As some other responses said, when there is no exception, nothing is raised.
Therefore, you can just your code for the "no-exception" into the try block after the rest of instructions. Something like:
try{
//code here
//code of no exception
}catch(Exception e){
//nothing or exception code
}
or you can just create your own exception by doing a class that extends Exception
I am a beginner in java and I used Delphi for a long time.
When I want to leave a method I need to use the exit() method and in Java I use return.
To abort all subsequent methods I call the abort() method in Delphi. How to do this in Java?
There's no direct support in Java for what you're asking, but in a non-elegant way you could simulate abort's behavior by throwing an exception and catching it wherever you see fit in your code.
Using System.exit(0) would not be the same, that method call will exit your program without any chance to recover along the way.
If you use abort like in this link (http://www.delphibasics.co.uk/RTL.asp?Name=Abort),
i think this functionality is similar with throw see this link
http://www.roseindia.net/java/exceptions/how-to-throw-exceptions.shtml
http://en.wikibooks.org/wiki/Java_Programming/Throwing_and_Catching_Exceptions
try {
this.interrupt();
} catch (IllegalThreadStateException e) {
e.printStackTrace();
}
I found out that an IllegalThreadStateException was thrown by putting print statement, no stack trace was printed. I have tried searching existing threads about Thread.interrupt() and IllegalThreadStateException, but didn't get much out of them. I am using CDLC 1.1, if it helps. thank you very much!!
CLDC 1.1 is supposed to support interrupt(), but CLDC 1.0 didn't. Maybe your particular implementation didn't feel like adding this support, and fakes it by throwing a runtime exception.
If no stack trace is printed, it sounds like there error is happening (and being handled) elsewhere. Can you step through the code in a debugger and see if that interrupt is triggering another thread to have a problem? It would have to occur with the process of executing interrupt().
In our IDE, I would put a breakpoint on that line, hit F5 to step inside the method call, then continue stepping inside until I found the problem. Along the way, if I get to a point where there is no source code I would download the related source jar file and point the debugger to it (which sounds involved but only takes about 2 minutes).
Hope that helps in some way,
-gMale
I am trying to solve the collatz conjecture.
I am using HashMap and Vector classes. I have to iterate the loop 2 147 483 648 times, but after I store 8,438,409 values in HashMap I'm getting an OutOfMemoryError.
I'm running the program in Eclipse and have set -Xmx1024m option, but it didn't help. So, I'm catching the above error and trying to start a thread which would take the control to different class and start executing.
However, the thread is not starting. I've put System.out.println("We are here"); statement in it and it's never printed to the console. Can someone help me with this?
Thanks
funny
You don't want to start a thread in your catch {} block. That's trying (and failing) to treat the symptoms while ignoring the cause entirely.
What you want to do is stop that OutOfMemory error from occurring. Your options are to increase the heap size, or use less of it.
You have stumbled onto the difference between an exception and an error in java. Both errors and exceptions descend from throwable but just catching an exception will not catch an error. However errors are usually pretty serious and are difficult if not impossible to recover from see. When to catch java.lang.Error?
Yes you can start a thread in a catch block.
However, you probably won't be able to start a thread if you're getting an OutOfMemoryError. OutOfMemoryError means you're running out of heap space, and all threads use the same heap space (and in fact, creating a new thread will use up some of your already diminished heap).
You shouldn't need to iterate over every value to solve a question based on the collatz conjecture. I'd assume you are trying to calculate each value. This is an approach that I tried but ran in to the same thing (though, I was using .net).
Rather than trying to solve the technical problem, I'd like to suggest that you alter your approach.
Note: I realized, I assumed (with no cause), that you are trying to solve a ProjectEuler.net question (or the alike). If this is not the case, my solution may not be viable.
Yes,
there is no restriction on starting a thread in a catch block. However, the nomal behavior when capturing an exception is show it to users, logging, throw another exception instead, close your application.
As said for the others, in your case you're trying to catch a java.lang.Error, which is not an Exception, and you don't have guarante of the next line of code execution.