Variable might not have been initialized error

Question

When I try to compile this  public static Rand searchCount  int   x        int a       int b                 for  int l  0  l lt x length  l                  if  x l     0          a             else if  x l     1          b                        I get these errors  Rand java 72  variable a might not have been initialized                 a                       Rand java 74  variable b might not have been initialized                 b                       2 errors  It seems to me that I initialized them at the top of the method  What s going wrong

User · Answer

Imagine what happens if x l  is neither 0 nor 1 in the loop  In that case a and b will never be assigned to and have an undefined value  You must initialize them both with some value  for example 0

User · Answer

Local variables do not get default values  Their initial values are undefined with out assigning values by some means  Before you can use local variables they must be initialized   There is a big difference when you declare a variable at class level  as a member ie  as a field  and at method level   If you declare a field at class level they get default values according to their type  If you declare a variable at method level or as a block  means anycode inside     do not get any values and remain undefined until somehow they get some starting values ie some values assigned to them

User · Answer

If they were declared as fields of the class then they would be really initialized with 0   You re a bit confused because if you write   class Clazz     int a    int b     Clazz           super          b   0         public void printA           sout  a   b          public static void main  String   args         new Clazz    printA             Then this code will print  0   It s because a special constructor will be called when you create new instance of Clazz  At first super    will be called  then field a will be initialized implicitly  and then line b   0 will be executed

User · Answer

It s a good practice to initialize the local variables inside the method block before using it  Here is a mistake that a beginner may commit     public static void main String   args       int a      int   arr    1 2 3 4 5       for int i 0  i lt arr length  i             a   arr i             System out println a         You may expect the console will show  5  but instead the compiler will throw  variable a might not be initialized  error  Though one may think variable a is  initialized  inside the for loop  the compiler does not think in that way  What if arr length is 0  The for loop will not be run at all  Hence  the compiler will give variable a might not have been initialized to point out the potential danger and require you to initialize the variable   To prevent this kind of error  just initialize the variable when you declare it   int a   0

User · Answer

You declared them but did not provide them with an intial value - thus  they re unintialized   Try something like   public static Rand searchCount  int   x         int a   0       int b   0      and the warnings should go away

User · Answer

You declared them  but not initialized   int a     declaration  unknown value a   0     initialization int a   0     declaration with initialization

User · Answer

Since no other answer has cited the Java language standard  I have decided to write an answer of my own  In Java  local variables are not  by default  initialized with a certain value  unlike  for example  the field of classes   From the language specification one    4 12 5  can read the following   A local variable    14 4    14 14  must be explicitly given a value before it is used  by either initialization    14 4  or assignment    15 26   in a way that can be verified using the rules for definite assignment    16  Definite Assignment     Therefore  since the variables a and b are not initialized    for  int l  0  l lt x length  l                   if  x l     0           a             else if  x l     1           b            the operations a    and b    could not produce any meaningful results  anyway  So it is logical for the compiler to notify you about it  Rand java 72  variable a might not have been initialized                 a                       Rand java 74  variable b might not have been initialized                 b                        However  one needs to understand that the fact that a    and b    could not produce any meaningful results has nothing to do with the reason why the compiler displays an error  But rather because it is explicitly set on the Java language specification that  A local variable    14 4    14 14  must be explicitly given a value        To showcase the aforementioned point  let us change a bit your code to  public static Rand searchCount  int   x         if x    null    x length     0        return null      int a        int b                     for  int l  0  l lt x length  l                   if l    0             a   l          if l    1             b   l                       So even though the code above can be formally proven to be valid  i e   the variables a and b will be always assigned with the value 0 and 1  respectively  it is not the compiler job to try to analyze your application s logic  and neither does the rules of local variable initialization rely on that  The compiler checks if the variables a and b are initialized according to the local variable initialization rules  and reacts accordingly  e g   displaying a compilation error

User · Answer

You haven t initialised a and b  only declared them   There is a subtle difference   int a   0  int b   0    At least this is for C    I presume Java is the same concept

User · Answer

Set variable  a  to some value like this   a 0    Declaring and initialzing are both different    Good Luck

User · Answer

because of your a and b variable is not have been initialized  You must initialized this variables for excample if you declare this variable like this int a 0  int b 0  than your code run without error

User · Answer

You declared them  but you didn t initialize them  Initializing them is setting them equal to a value   int a            This is a declaration a   0            This is an initialization int b   1        This is a declaration and initialization   You get the error because you haven t initialized the variables  but you increment them  e g   a    in the for loop   Java primitives have default values but as one user commented below     Their default value is zero when declared as class members  Local variables don t have default values

User · Answer

You declared them at the start of the method  but you never initialized them  Initializing would be setting them equal to a value  such as   int a   0  int b   0

User · Answer

You declared them  but you didn t initialize them with a value  Add something like this  int a   0

[java] Variable might not have been initialized error

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