When to catch java lang Error

Question

In what situations should one catch java lang Error on an application

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Generally you should always catch java lang Error and write it to a log or display it to the user  I work in support and see daily that programmers cannot tell what has happened in a program   If you have a daemon thread then you must prevent it being terminated  In other cases your application will work correctly   You should only catch java lang Error at the highest level   If you look at the list of errors you will see that most can be handled  For example a ZipError occurs on reading corrupt zip files   The most common errors are OutOfMemoryError and NoClassDefFoundError  which are both in most cases runtime problems   For example   int length   Integer parseInt xyz   byte   buffer   new byte length     can produce an OutOfMemoryError but it is a runtime problem and no reason to terminate your program   NoClassDefFoundError occur mostly if a library is not present or if you work with another Java version  If it is an optional part of your program then you should not terminate your program   I can give many more examples of why it is a good idea to catch Throwable at the top level and produce a helpful error message

User · Answer

An Error usually shouldn t be caught  as it indicates an abnormal condition that should never occur   From the Java API Specification for the Error class      An Error is a subclass of Throwable   that indicates serious problems that a   reasonable application should not try   to catch  Most such errors are   abnormal conditions             A method is not required to declare in   its throws clause any subclasses of   Error that might be thrown during the   execution of the method but not   caught  since these errors are   abnormal conditions that should never   occur    As the specification mentions  an Error is only thrown in circumstances that are  Chances are  when an Error occurs  there is very little the application can do  and in some circumstances  the Java Virtual Machine itself may be in an unstable state  such as VirtualMachineError   Although an Error is a subclass of Throwable which means that it can be caught by a try-catch clause  but it probably isn t really needed  as the application will be in an abnormal state when an Error is thrown by the JVM   There s also a short section on this topic in Section 11 5 The Exception Hierarchy of the Java Language Specification  2nd Edition

User · Answer

Ideally we should not handle catch errors  But there may be cases where we need to do  based on requirement of framework or application  Say i have a XML Parser daemon which implements DOM Parser which consumes more Memory  If there is a requirement like Parser thread should not be died when it gets OutOfMemoryError  instead it should handle it and send a message mail to administrator of application framework

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Almost never  Errors are designed to be issues that applications generally can t do anything about  The only exception might be to handle the presentation of the error but even that might not go as planned depending on the error

User · Answer

Very rarely   I d say only at the top level of a thread in order to ATTEMPT to issue a message with the reason for a thread dying   If you are in a framework that does this sort of thing for you  leave it to the framework

User · Answer

Very rarely   I d say only at the top level of a thread in order to ATTEMPT to issue a message with the reason for a thread dying   If you are in a framework that does this sort of thing for you  leave it to the framework

User · Answer

If you are crazy enough to be creating a new unit test framework  your test runner will probably need to catch java lang AssertionError thrown by any test cases   Otherwise  see other answers

User · Answer

Very  very rarely   I did it only for one very very specific known cases  For example  java lang UnsatisfiedLinkError could be throw if two independence ClassLoader load same DLL   I agree that I should move the JAR to a shared classloader   But most common case is that you needed logging in order to know what happened when user come to complain  You want a message or a popup to user  rather then silently dead   Even programmer in C C    they pop an error and tell something people don t understand  before it exit  e g  memory failure

User · Answer

And there are a couple of other cases where if you catch an Error  you have to rethrow it  For example ThreadDeath should never be caught  it can cause big problem is you catch it in a contained environment  eg  an application server        An application should catch instances of this class only if it must clean up   after being terminated asynchronously  If ThreadDeath is caught by a method    it is important that it be rethrown so that the thread actually dies

User · Answer

Ideally we should not handle catch errors  But there may be cases where we need to do  based on requirement of framework or application  Say i have a XML Parser daemon which implements DOM Parser which consumes more Memory  If there is a requirement like Parser thread should not be died when it gets OutOfMemoryError  instead it should handle it and send a message mail to administrator of application framework

User · Answer

If you are crazy enough to be creating a new unit test framework  your test runner will probably need to catch java lang AssertionError thrown by any test cases   Otherwise  see other answers

User · Answer

Almost never  Errors are designed to be issues that applications generally can t do anything about  The only exception might be to handle the presentation of the error but even that might not go as planned depending on the error

User · Answer

Generally you should always catch java lang Error and write it to a log or display it to the user  I work in support and see daily that programmers cannot tell what has happened in a program   If you have a daemon thread then you must prevent it being terminated  In other cases your application will work correctly   You should only catch java lang Error at the highest level   If you look at the list of errors you will see that most can be handled  For example a ZipError occurs on reading corrupt zip files   The most common errors are OutOfMemoryError and NoClassDefFoundError  which are both in most cases runtime problems   For example   int length   Integer parseInt xyz   byte   buffer   new byte length     can produce an OutOfMemoryError but it is a runtime problem and no reason to terminate your program   NoClassDefFoundError occur mostly if a library is not present or if you work with another Java version  If it is an optional part of your program then you should not terminate your program   I can give many more examples of why it is a good idea to catch Throwable at the top level and produce a helpful error message

User · Answer

Never  You can never be sure that the application is able to execute the next line of code  If you get an OutOfMemoryError  you have no guarantee that you will be able to do anything reliably  Catch RuntimeException and checked Exceptions  but never Errors   http   pmd sourceforge net rules strictexception html

User · Answer

Never  You can never be sure that the application is able to execute the next line of code  If you get an OutOfMemoryError  you have no guarantee that you will be able to do anything reliably  Catch RuntimeException and checked Exceptions  but never Errors   http   pmd sourceforge net rules strictexception html

User · Answer

Very rarely   I d say only at the top level of a thread in order to ATTEMPT to issue a message with the reason for a thread dying   If you are in a framework that does this sort of thing for you  leave it to the framework

User · Answer

Generally  never   However  sometimes you need to catch specific errors   If you re writing framework-ish code  loading 3rd party classes   it might be wise to catch LinkageError  no class def found  unsatisfied link  incompatible class change     I ve also seen some stupid 3rd-party code throwing subclasses of Error  so you ll have to handle those as well   By the way  I m not sure it isn t possible to recover from OutOfMemoryError

User · Answer

An Error usually shouldn t be caught  as it indicates an abnormal condition that should never occur   From the Java API Specification for the Error class      An Error is a subclass of Throwable   that indicates serious problems that a   reasonable application should not try   to catch  Most such errors are   abnormal conditions             A method is not required to declare in   its throws clause any subclasses of   Error that might be thrown during the   execution of the method but not   caught  since these errors are   abnormal conditions that should never   occur    As the specification mentions  an Error is only thrown in circumstances that are  Chances are  when an Error occurs  there is very little the application can do  and in some circumstances  the Java Virtual Machine itself may be in an unstable state  such as VirtualMachineError   Although an Error is a subclass of Throwable which means that it can be caught by a try-catch clause  but it probably isn t really needed  as the application will be in an abnormal state when an Error is thrown by the JVM   There s also a short section on this topic in Section 11 5 The Exception Hierarchy of the Java Language Specification  2nd Edition

User · Answer

ideally we should never catch Error in our Java application as it is an abnormal condition  The application would be in abnormal state and could result in carshing or giving some seriously wrong result

User · Answer

If you are crazy enough to be creating a new unit test framework  your test runner will probably need to catch java lang AssertionError thrown by any test cases   Otherwise  see other answers

User · Answer

And there are a couple of other cases where if you catch an Error  you have to rethrow it  For example ThreadDeath should never be caught  it can cause big problem is you catch it in a contained environment  eg  an application server        An application should catch instances of this class only if it must clean up   after being terminated asynchronously  If ThreadDeath is caught by a method    it is important that it be rethrown so that the thread actually dies

User · Answer

Almost never  Errors are designed to be issues that applications generally can t do anything about  The only exception might be to handle the presentation of the error but even that might not go as planned depending on the error

User · Answer

There is an Error when the JVM is no more working as expected  or is on the verge to  If you catch an error  there is no guarantee that the catch block will run  and even less that it will run till the end   It will also depend on the running computer  the current memory state  so there is no way to test  try and do your best  You will only have an hasardous result   You will also downgrade the readability of your code

User · Answer

And there are a couple of other cases where if you catch an Error  you have to rethrow it  For example ThreadDeath should never be caught  it can cause big problem is you catch it in a contained environment  eg  an application server        An application should catch instances of this class only if it must clean up   after being terminated asynchronously  If ThreadDeath is caught by a method    it is important that it be rethrown so that the thread actually dies

User · Answer

In an Android application I am catching a java lang VerifyError  A library that I am using won t work in devices with an old version of the OS and the library code will throw such an error  I could of course avoid the error by checking the version of OS at runtime  but    The oldest supported SDK may change in future for the specific library The try-catch error block is part of a bigger falling back mechanism  Some specific devices  although they are supposed to support the library  throw exceptions  I catch VerifyError and all Exceptions to use a fall back solution

User · Answer

Generally  never   However  sometimes you need to catch specific errors   If you re writing framework-ish code  loading 3rd party classes   it might be wise to catch LinkageError  no class def found  unsatisfied link  incompatible class change     I ve also seen some stupid 3rd-party code throwing subclasses of Error  so you ll have to handle those as well   By the way  I m not sure it isn t possible to recover from OutOfMemoryError

User · Answer

An Error usually shouldn t be caught  as it indicates an abnormal condition that should never occur   From the Java API Specification for the Error class      An Error is a subclass of Throwable   that indicates serious problems that a   reasonable application should not try   to catch  Most such errors are   abnormal conditions             A method is not required to declare in   its throws clause any subclasses of   Error that might be thrown during the   execution of the method but not   caught  since these errors are   abnormal conditions that should never   occur    As the specification mentions  an Error is only thrown in circumstances that are  Chances are  when an Error occurs  there is very little the application can do  and in some circumstances  the Java Virtual Machine itself may be in an unstable state  such as VirtualMachineError   Although an Error is a subclass of Throwable which means that it can be caught by a try-catch clause  but it probably isn t really needed  as the application will be in an abnormal state when an Error is thrown by the JVM   There s also a short section on this topic in Section 11 5 The Exception Hierarchy of the Java Language Specification  2nd Edition

User · Answer

Almost never  Errors are designed to be issues that applications generally can t do anything about  The only exception might be to handle the presentation of the error but even that might not go as planned depending on the error

User · Answer

It might be appropriate to catch error within unit tests that check an assertion is made  If someone disables assertions or otherwise deletes the assertion you would want to know

User · Answer

In multithreaded environment  you most often want to catch it  When you catch it  log it  and terminate whole application  If you don t do that  some thread that might be doing some crucial part would be dead  and rest of the application will think that everything is normal  Out of that  many unwanted situations can happen   One smallest problem is that you wouldn t be able to easily find root of the problem  if other threads start throwing some exceptions because of one thread not working   For example  usually loop should be   try      while  shouldRun             doSomething           catch  Throwable t       log t      stop       System exit 1       Even in some cases  you would want to handle different Errors differently  for example  on OutOfMemoryError you would be able to close application regularly  even maybe free some memory  and continue   on some others  there is not much you can do

User · Answer

it s quite handy to catch java lang AssertionError in a test environment

User · Answer

There is an Error when the JVM is no more working as expected  or is on the verge to  If you catch an error  there is no guarantee that the catch block will run  and even less that it will run till the end   It will also depend on the running computer  the current memory state  so there is no way to test  try and do your best  You will only have an hasardous result   You will also downgrade the readability of your code

User · Answer

Very  very rarely   I did it only for one very very specific known cases  For example  java lang UnsatisfiedLinkError could be throw if two independence ClassLoader load same DLL   I agree that I should move the JAR to a shared classloader   But most common case is that you needed logging in order to know what happened when user come to complain  You want a message or a popup to user  rather then silently dead   Even programmer in C C    they pop an error and tell something people don t understand  before it exit  e g  memory failure

User · Answer

Never  You can never be sure that the application is able to execute the next line of code  If you get an OutOfMemoryError  you have no guarantee that you will be able to do anything reliably  Catch RuntimeException and checked Exceptions  but never Errors   http   pmd sourceforge net rules strictexception html

User · Answer

In multithreaded environment  you most often want to catch it  When you catch it  log it  and terminate whole application  If you don t do that  some thread that might be doing some crucial part would be dead  and rest of the application will think that everything is normal  Out of that  many unwanted situations can happen   One smallest problem is that you wouldn t be able to easily find root of the problem  if other threads start throwing some exceptions because of one thread not working   For example  usually loop should be   try      while  shouldRun             doSomething           catch  Throwable t       log t      stop       System exit 1       Even in some cases  you would want to handle different Errors differently  for example  on OutOfMemoryError you would be able to close application regularly  even maybe free some memory  and continue   on some others  there is not much you can do

User · Answer

Generally  never   However  sometimes you need to catch specific errors   If you re writing framework-ish code  loading 3rd party classes   it might be wise to catch LinkageError  no class def found  unsatisfied link  incompatible class change     I ve also seen some stupid 3rd-party code throwing subclasses of Error  so you ll have to handle those as well   By the way  I m not sure it isn t possible to recover from OutOfMemoryError

User · Answer

Generally  never   However  sometimes you need to catch specific errors   If you re writing framework-ish code  loading 3rd party classes   it might be wise to catch LinkageError  no class def found  unsatisfied link  incompatible class change     I ve also seen some stupid 3rd-party code throwing subclasses of Error  so you ll have to handle those as well   By the way  I m not sure it isn t possible to recover from OutOfMemoryError

User · Answer

An Error usually shouldn t be caught  as it indicates an abnormal condition that should never occur   From the Java API Specification for the Error class      An Error is a subclass of Throwable   that indicates serious problems that a   reasonable application should not try   to catch  Most such errors are   abnormal conditions             A method is not required to declare in   its throws clause any subclasses of   Error that might be thrown during the   execution of the method but not   caught  since these errors are   abnormal conditions that should never   occur    As the specification mentions  an Error is only thrown in circumstances that are  Chances are  when an Error occurs  there is very little the application can do  and in some circumstances  the Java Virtual Machine itself may be in an unstable state  such as VirtualMachineError   Although an Error is a subclass of Throwable which means that it can be caught by a try-catch clause  but it probably isn t really needed  as the application will be in an abnormal state when an Error is thrown by the JVM   There s also a short section on this topic in Section 11 5 The Exception Hierarchy of the Java Language Specification  2nd Edition

User · Answer

Never  You can never be sure that the application is able to execute the next line of code  If you get an OutOfMemoryError  you have no guarantee that you will be able to do anything reliably  Catch RuntimeException and checked Exceptions  but never Errors   http   pmd sourceforge net rules strictexception html

User · Answer

It might be appropriate to catch error within unit tests that check an assertion is made  If someone disables assertions or otherwise deletes the assertion you would want to know

User · Answer

it s quite handy to catch java lang AssertionError in a test environment

User · Answer

Very  very rarely   I did it only for one very very specific known cases  For example  java lang UnsatisfiedLinkError could be throw if two independence ClassLoader load same DLL   I agree that I should move the JAR to a shared classloader   But most common case is that you needed logging in order to know what happened when user come to complain  You want a message or a popup to user  rather then silently dead   Even programmer in C C    they pop an error and tell something people don t understand  before it exit  e g  memory failure

User · Answer

In an Android application I am catching a java lang VerifyError  A library that I am using won t work in devices with an old version of the OS and the library code will throw such an error  I could of course avoid the error by checking the version of OS at runtime  but    The oldest supported SDK may change in future for the specific library The try-catch error block is part of a bigger falling back mechanism  Some specific devices  although they are supposed to support the library  throw exceptions  I catch VerifyError and all Exceptions to use a fall back solution

User · Answer

Very rarely   I d say only at the top level of a thread in order to ATTEMPT to issue a message with the reason for a thread dying   If you are in a framework that does this sort of thing for you  leave it to the framework

User · Answer

ideally we should never catch Error in our Java application as it is an abnormal condition  The application would be in abnormal state and could result in carshing or giving some seriously wrong result

User · Answer

If you are crazy enough to be creating a new unit test framework  your test runner will probably need to catch java lang AssertionError thrown by any test cases   Otherwise  see other answers

User · Answer

Very  very rarely   I did it only for one very very specific known cases  For example  java lang UnsatisfiedLinkError could be throw if two independence ClassLoader load same DLL   I agree that I should move the JAR to a shared classloader   But most common case is that you needed logging in order to know what happened when user come to complain  You want a message or a popup to user  rather then silently dead   Even programmer in C C    they pop an error and tell something people don t understand  before it exit  e g  memory failure

User · Answer

And there are a couple of other cases where if you catch an Error  you have to rethrow it  For example ThreadDeath should never be caught  it can cause big problem is you catch it in a contained environment  eg  an application server        An application should catch instances of this class only if it must clean up   after being terminated asynchronously  If ThreadDeath is caught by a method    it is important that it be rethrown so that the thread actually dies

[java] When to catch java.lang.Error?

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