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unable to understand the output

nishant vats
Greenhorn
Posts: 23
int[] a = new int[2];
int n =0;
a[++n]= ++n;

System.out.println("the array contains "+ a[0] +a[1]);

output 0 2

can u explain what is logic behind output and if i change it to
a[n++]=++n;
then output is
output 2 0

Andris Jekabsons
Ranch Hand
Posts: 82
In the first example "a[ ++n ]" the increment is performed BEFORE evaluating the value of n.
So, the expressions becomes "a[ 0+1 ] = ++n", that is: "a[ 1 ] = ++n".
n now has value of 1, and it is incremented on the left side of " = ":
"a[ 1 ] = 1+1", that is: "a[ 1 ] = 2"
a[ 0 ] remains with the default value of 0.

In the second example "a[ ++n ]" the increment is performed AFTER evaluating the value of n.
So, the expressions becomes "a[ 0 ] = ++n".
Only then n is assigned the value of 1, and it is incremented on the left side of " = ":
"a[ 0 ] = 1+1", that is: "a[ 0 ] = 2"
a[ 1 ] remains with the default value of 0.

nishant vats
Greenhorn
Posts: 23
thanks for reply but i guess in assignment operator right hand evaluation is done before ..in that case ++n is evaluated first.. so can u nw explain the answer

Joe Sondow
Ranch Hand
Posts: 195
nish vats, that seems like a reasonable assumption but it turns out to be incorrect. The left-hand operand is evaluated first in order to determine the variable that will receive the newly assigned value. The entire procedure is described in the JLS 15.26.1.

nishant vats
Greenhorn
Posts: 23
thanks joe ...