Java array reflection isArray vs instanceof

Question

Is there a preference or behavior difference between using   if obj getClass   isArray         and  if obj instanceof Object

User · Answer

If you ever have a choice between a reflective solution and a non-reflective solution  never pick the reflective one  involving Class objects    It s not that it s  Wrong  or anything  but anything involving reflection is generally less obvious and less clear

User · Answer

If you ever have a choice between a reflective solution and a non-reflective solution  never pick the reflective one  involving Class objects    It s not that it s  Wrong  or anything  but anything involving reflection is generally less obvious and less clear

User · Answer

If obj is of type int   say  then that will have an array Class but not be an instance of Object    So what do you want to do with obj  If you are going to cast it  go with instanceof  If you are going to use reflection  then use  getClass   isArray

User · Answer

In the latter case  if obj is null you won t get a NullPointerException but a false

User · Answer

There is no difference in behavior that I can find between the two  other than the obvious null-case   As for which version to prefer  I would go with the second  It is the standard way of doing this in Java   If it confuses readers of your code  because String   instanceof Object   is true   you may want to use the first to be more explicit if code reviewers keep asking about it

User · Answer

If obj is of type int   say  then that will have an array Class but not be an instance of Object    So what do you want to do with obj  If you are going to cast it  go with instanceof  If you are going to use reflection  then use  getClass   isArray

User · Answer

There is no difference in behavior that I can find between the two  other than the obvious null-case   As for which version to prefer  I would go with the second  It is the standard way of doing this in Java   If it confuses readers of your code  because String   instanceof Object   is true   you may want to use the first to be more explicit if code reviewers keep asking about it

User · Answer

In most cases  you should use the instanceof operator to test whether an object is an array   Generally  you test an object s type before downcasting to a particular type which is known at compile time  For example  perhaps you wrote some code that can work with a Integer   or an int    You d want to guard your casts with instanceof   if  obj instanceof Integer          Integer   array    Integer    obj         Use the boxed array      else if  obj instanceof int          int   array    int    obj         Use the primitive array      else       At the JVM level  the instanceof operator translates to a specific  instanceof  byte code  which is optimized in most JVM implementations   In rarer cases  you might be using reflection to traverse an object graph of unknown types  In cases like this  the isArray   method can be helpful because you don t know the component type at compile time  you might  for example  be implementing some sort of serialization mechanism and be able to pass each component of the array to the same serialization method  regardless of type   There are two special cases  null references and references to primitive arrays   A null reference will cause instanceof to result false  while the isArray throws a NullPointerException   Applied to a primitive array  the instanceof yields false unless the component type on the right-hand operand exactly matches the component type  In contrast  isArray   will return true for any component type

User · Answer

In most cases  you should use the instanceof operator to test whether an object is an array   Generally  you test an object s type before downcasting to a particular type which is known at compile time  For example  perhaps you wrote some code that can work with a Integer   or an int    You d want to guard your casts with instanceof   if  obj instanceof Integer          Integer   array    Integer    obj         Use the boxed array      else if  obj instanceof int          int   array    int    obj         Use the primitive array      else       At the JVM level  the instanceof operator translates to a specific  instanceof  byte code  which is optimized in most JVM implementations   In rarer cases  you might be using reflection to traverse an object graph of unknown types  In cases like this  the isArray   method can be helpful because you don t know the component type at compile time  you might  for example  be implementing some sort of serialization mechanism and be able to pass each component of the array to the same serialization method  regardless of type   There are two special cases  null references and references to primitive arrays   A null reference will cause instanceof to result false  while the isArray throws a NullPointerException   Applied to a primitive array  the instanceof yields false unless the component type on the right-hand operand exactly matches the component type  In contrast  isArray   will return true for any component type

User · Answer

Java array reflection is for cases where you don t have an instance of the Class available to do  instanceof  on   For example  if you re writing some sort of injection framework  that injects values into a new instance of a class  such as JPA does  then you need to use the isArray   functionality   I blogged about this earlier in December  http   blog adamsbros org 2010 12 08 java-array-reflection

User · Answer

In the latter case  if obj is null you won t get a NullPointerException but a false

User · Answer

If obj is of type int   say  then that will have an array Class but not be an instance of Object    So what do you want to do with obj  If you are going to cast it  go with instanceof  If you are going to use reflection  then use  getClass   isArray

User · Answer

I recently ran into an issue upgrading a Groovy application from JDK 5 to JDK 6   Using isArray   failed in JDK6   MissingMethodException  No signature of sun reflect generics reflectiveObjects GenericArrayTypeImpl isArray         Changing to instanceof Object   fixed this

User · Answer

I recently ran into an issue upgrading a Groovy application from JDK 5 to JDK 6   Using isArray   failed in JDK6   MissingMethodException  No signature of sun reflect generics reflectiveObjects GenericArrayTypeImpl isArray         Changing to instanceof Object   fixed this

User · Answer

In the latter case  if obj is null you won t get a NullPointerException but a false

User · Answer

There is no difference in behavior that I can find between the two  other than the obvious null-case   As for which version to prefer  I would go with the second  It is the standard way of doing this in Java   If it confuses readers of your code  because String   instanceof Object   is true   you may want to use the first to be more explicit if code reviewers keep asking about it

User · Answer

If you ever have a choice between a reflective solution and a non-reflective solution  never pick the reflective one  involving Class objects    It s not that it s  Wrong  or anything  but anything involving reflection is generally less obvious and less clear

User · Answer

If you ever have a choice between a reflective solution and a non-reflective solution  never pick the reflective one  involving Class objects    It s not that it s  Wrong  or anything  but anything involving reflection is generally less obvious and less clear

User · Answer

getClass   isArray   is significantly slower on Sun Java 5 or 6 JRE than on IBM   So much that using clazz getName   charAt 0         is faster on Sun JVM

User · Answer

If obj is of type int   say  then that will have an array Class but not be an instance of Object    So what do you want to do with obj  If you are going to cast it  go with instanceof  If you are going to use reflection  then use  getClass   isArray

User · Answer

In most cases  you should use the instanceof operator to test whether an object is an array   Generally  you test an object s type before downcasting to a particular type which is known at compile time  For example  perhaps you wrote some code that can work with a Integer   or an int    You d want to guard your casts with instanceof   if  obj instanceof Integer          Integer   array    Integer    obj         Use the boxed array      else if  obj instanceof int          int   array    int    obj         Use the primitive array      else       At the JVM level  the instanceof operator translates to a specific  instanceof  byte code  which is optimized in most JVM implementations   In rarer cases  you might be using reflection to traverse an object graph of unknown types  In cases like this  the isArray   method can be helpful because you don t know the component type at compile time  you might  for example  be implementing some sort of serialization mechanism and be able to pass each component of the array to the same serialization method  regardless of type   There are two special cases  null references and references to primitive arrays   A null reference will cause instanceof to result false  while the isArray throws a NullPointerException   Applied to a primitive array  the instanceof yields false unless the component type on the right-hand operand exactly matches the component type  In contrast  isArray   will return true for any component type

User · Answer

There is no difference in behavior that I can find between the two  other than the obvious null-case   As for which version to prefer  I would go with the second  It is the standard way of doing this in Java   If it confuses readers of your code  because String   instanceof Object   is true   you may want to use the first to be more explicit if code reviewers keep asking about it

User · Answer

Java array reflection is for cases where you don t have an instance of the Class available to do  instanceof  on   For example  if you re writing some sort of injection framework  that injects values into a new instance of a class  such as JPA does  then you need to use the isArray   functionality   I blogged about this earlier in December  http   blog adamsbros org 2010 12 08 java-array-reflection

User · Answer

getClass   isArray   is significantly slower on Sun Java 5 or 6 JRE than on IBM   So much that using clazz getName   charAt 0         is faster on Sun JVM

User · Answer

In the latter case  if obj is null you won t get a NullPointerException but a false

User · Answer

In most cases  you should use the instanceof operator to test whether an object is an array   Generally  you test an object s type before downcasting to a particular type which is known at compile time  For example  perhaps you wrote some code that can work with a Integer   or an int    You d want to guard your casts with instanceof   if  obj instanceof Integer          Integer   array    Integer    obj         Use the boxed array      else if  obj instanceof int          int   array    int    obj         Use the primitive array      else       At the JVM level  the instanceof operator translates to a specific  instanceof  byte code  which is optimized in most JVM implementations   In rarer cases  you might be using reflection to traverse an object graph of unknown types  In cases like this  the isArray   method can be helpful because you don t know the component type at compile time  you might  for example  be implementing some sort of serialization mechanism and be able to pass each component of the array to the same serialization method  regardless of type   There are two special cases  null references and references to primitive arrays   A null reference will cause instanceof to result false  while the isArray throws a NullPointerException   Applied to a primitive array  the instanceof yields false unless the component type on the right-hand operand exactly matches the component type  In contrast  isArray   will return true for any component type

[java] Java array reflection: isArray vs. instanceof

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