What is the difference between i i in a for loop

Question

I ve just started learning Java and now I m into for loop statements  I don t understand how   i and i   works in a for-loop   How do they work in mathematics operations like addition and subtraction

User · Answer

Both i   and   i are short-hand for i   i   1   In addition to changing the value of i  they also return the value of i  either before adding one  i    or after adding one    i    In a loop the third component is a piece of code that is executed after each iteration   for  int i 0  i lt 10  i      The value of that part is not used  so the above is just the same as  for int i 0  i lt 10  i   i 1    or  for int i 0  i lt 10    i    Where it makes a difference  between i   and   i  is in these cases  while i    lt  10   for  int i 0  i    lt  10

User · Answer

The difference is that the post-increment operator i   returns i as it was before incrementing  and the pre-increment operator   i returns i as it is after incrementing    If you re asking about a typical for loop   for  i   0  i  lt  10  i      or  for  i   0  i  lt  10    i    They re exactly the same  since you re not using i   or   i as a part of a larger expression

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Both of them increase the variable i by one  It s like saying i   i   1  The difference is subtle  If you re using it in a loop like this  there s no difference   for  int i   0  i  lt  100  i         for  int i   0  i  lt  100    i        If you want to know the difference  look at this example   int a   0  int b   a       b   0  a   1  a   0  b     a     b   1  a   1   The idea is that   a increments a and returns that value  while a   returns a s value and then increments a

User · Answer

JLS  14 14 1  The basic for Statement  makes it clear that the ForUpdate expression s  are evaluated and the value s  are discarded  The effect is to make the two forms identical in the context of a for statement

User · Answer

They both increment the number    i is equivalent to i   i   1   i   and   i are very similar but not exactly the same  Both increment the number  but   i increments the number before the current expression is evaluted  whereas i   increments the number after the expression is evaluated   int i   3  int a   i       a   3  i   4 int b     a     b   4  a   4

User · Answer

The way for loop is processed is as follows  1 First  initialization is performed  i 0   2 the check is performed  i  lt  n   3 the code in the loop is executed   4 the value is incremented  5 Repeat steps 2 - 4  This is the reason why  there is no difference between i   and   i in the for loop which has been used

User · Answer

Here s a sample class    public class Increment       public static void main String    args                for  int i   0  i  lt  args length    i                        System out println args i                        If I disassemble this class using javap exe I get this    Compiled from  Increment java  public class Increment extends java lang Object  public Increment      Code     0    aload 0    1    invokespecial    1    Method java lang Object   lt init gt     V    4    return  public static void main java lang String       Code     0    iconst 0    1    istore 1    2    iload 1    3    aload 0    4    arraylength    5    if icmpge       23    8    getstatic        2    Field java lang System out Ljava io PrintStream     11   aload 0    12   iload 1    13   aaload    14   invokevirtual    3    Method java io PrintStream println  Ljava lang String  V    17   iinc    1  1    20   goto    2    23   return      If I change the loop so it uses i   and disassemble again I get this    Compiled from  Increment java  public class Increment extends java lang Object  public Increment      Code     0    aload 0    1    invokespecial    1    Method java lang Object   lt init gt     V    4    return  public static void main java lang String       Code     0    iconst 0    1    istore 1    2    iload 1    3    aload 0    4    arraylength    5    if icmpge       23    8    getstatic        2    Field java lang System out Ljava io PrintStream     11   aload 0    12   iload 1    13   aaload    14   invokevirtual    3    Method java io PrintStream println  Ljava lang String  V    17   iinc    1  1    20   goto    2    23   return      When I compare the two  TextPad tells me that the two are identical    What this says is that from the point of view of the generated byte code there s no difference in a loop   In other contexts there is a difference between   i and i    but not for loops

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