Java How to check if object is null

Question

I am creating an application which retrieves images from the web  In case the image cannot be retrieved another local image should be used   While trying to execute the following lines   Drawable drawable   Common getDrawableFromUrl this  product getMapPath     if  drawable equals null       drawable   getRandomDrawable        The line if drawable equals null   throws an exception if drawable is null   Does anyone know how should the value of drawable be checked in order not to throw an exception in case it is null and retrieve the local image  execute drawable   getRandomDrawable

User · Answer

I use this approach   if  null    drawable        do stuff   else       other things     This way I find improves the readability of the line - as I read quickly through a source file I can see it s a null check   With regards to why you can t call  equals   on an object which may be null  if the object reference you have  namely  drawable   is in fact null  it doesn t point to an object on the heap  This means there s no object on the heap on which the call to equals   can succeed   Best of luck

User · Answer

It s probably slightly more efficient to catch a NullPointerException  The above methods mean that the runtime is checking for null pointers twice

User · Answer

Drawable drawable   Common getDrawableFromUrl this  product getMapPath     if  drawable    null        drawable   getRandomDrawable        The equals   method checks for value equality  which means that it compares the contents of two objects  Since null is not an object  this crashes when trying to compare the contents of your object to the contents of null   The    operator checks for reference equality  which means that it looks whether the two objects are actually the very same object  This does not require the objects to actually exist  two nonexistent objects  null references  are also equal

User · Answer

Use google guava libs to handle is-null-check  deamon s update   Drawable drawable   Optional of Common getDrawableFromUrl this  product getMapPath     or getRandomDrawable

User · Answer

drawable equals null    The above line calls the  equals       method on the drawable object   So  when drawable is not null and it is a real object  then all goes well as calling the  equals null   method will return  false   But when  drawable  is null  then it means calling the  equals       method on null object  means calling a method on an object that doesn t exist so it throws  NullPointerException   To check whether an object exists and it is not null  use the following  if drawable    null                        In above condition  we are checking that the reference variable  drawable  is null or contains some value  reference to its object  so it won t throw exception in case drawable is null as checking   null    null   is valid

User · Answer

DIY  private boolean isNull Object obj        return obj    null        Drawable drawable   Common getDrawableFromUrl this  product getMapPath     if  isNull drawable         drawable   getRandomDrawable

User · Answer

if  yourObject instanceof yourClassName  will evaluate to false if yourObject is null

User · Answer

Edited Java 8 Solution   final Drawable drawable        Optional ofNullable Common getDrawableFromUrl this  product getMapPath              orElseGet    - gt  getRandomDrawable       You can declare drawable final in this case   As Chasmo pointed out  Android doesn t support Java 8 at the moment  So this solution is only possible in other contexts

User · Answer

Just to give some ideas to oracle Java source developer  -   The solution already exists in  Net and is more very more readable    In Visual Basic  Net  Drawable drawable        If Common getDrawableFromUrl this  product getMapPath             getRandomDrawable               In C   Drawable drawable        Common getDrawableFromUrl this  product getMapPath               getRandomDrawable      These solutions are powerful as Optional Java solution  default string is only evaluated if original value is null  without using lambda expression  just in adding a new operator    Just to see quickly the difference with Java solution  I have added the 2 Java solutions  Using Optional in Java  Drawable drawable        Optional ofNullable Common getDrawableFromUrl this  product getMapPath              orElseGet    - gt  getRandomDrawable       Using     in Java  Drawable drawable   Common getDrawableFromUrl this  product getMapPath     if  drawable    null            drawable   getRandomDrawable            Personally  I like VB Net but I prefer    C  or if    solution in Java     and you

[java] Java: How to check if object is null?

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