Java check to see if a variable has been initialized

Question

I need to use something similar to php s isset function  I know php and java are EXTREMELY different but php is my only basis of previous knowledge on something similar to programming  Is there some kind of method that would return a boolean value for whether or not an instance variable had been initialized or not  For example     if box isset        box removeFromCanvas        So far I ve had this problem where I am getting a run-time error when my program is trying to hide or remove an object that hasn t been constructed yet

User · Answer

Instance variables or fields  along with static variables  are assigned default values based on the variable type    int  0 char   u0000 or 0 double  0 0 boolean  false reference  null   Just want to clarify that local variables  ie  declared in block  eg  method  for loop  while loop  try-catch  etc   are not initialized to default values and must be explicitly initialized

User · Answer

Assuming you re interested in whether the variable has been explicitly assigned a value or not  the answer is  not really   There s absolutely no difference between a field  instance variable or class variable  which hasn t been explicitly assigned at all yet  and one which has been assigned its default value - 0  false  null etc   Now if you know that once assigned  the value will never reassigned a value of null  you can use   if  box    null        box removeFromCanvas         and that also avoids a possible NullPointerException  but you need to be aware that  a field with a value of null  isn t the same as  a field which hasn t been explicitly assigned a value   Null is a perfectly valid variable value  for non-primitive variables  of course   Indeed  you may even want to change the above code to   if  box    null        box removeFromCanvas           Forget about the box - we don t want to try to remove it again     box   null      The difference is also visible for local variables  which can t be read before they ve been  definitely assigned  - but one of the values which they can be definitely assigned is null  for reference type variables       Won t compile String x  System out println x       Will compile  prints null String y   null  System out println y

[java] Java check to see if a variable has been initialized

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