preincrement / postincrement in java

Question

Can someome help me to understand why:

int i=1;
int j=1;
int k=1;
int l=1;

System.out.println(i++ + i++);  
System.out.println(++j + ++j);  
System.out.pri         


        

Answer 1

i++ + i++

means use i, then increment, so i is pushed to some kind of stack,

then increased by 1,

then the operator (+) is pushed to the stack,

then i (now 2) is pushed to the stack.

Since the expresseion is now over, the values and operator are popped: the 2nd i is 2, the first i is 1, 2+1=3 (i is now 3, since it was incremented after being pushed).

The thing you are probably missing is that i isn't increased after the evaluation of the whole expression, in the case of a postincrement, and vice versa for preincrement.