Java- Why for uses i,j

Question

Possible Duplicate:
Why are we using i as a counter in loops?
Why are variables “i” and “j” used for counters?

This may seems stupid, but why everybody use i (if i is already in use, then j) in for loop checking ?

Means:

for(int i = 1;i <= 5;i++){
 for(int j = 1;j <= i;j++){
 System.out.print(i);
}

Why i and j ? We can use first and second also ? Check this, all (9 out of 10) uses i, j. Why ? Any reason or just doing because everybody does that ?

OK.. So, answer is, this is a tradition comes from MATH, PHYSICS, and FORTRAN. :) — Arpssss, Apr 17 '12 at 17:19
An excellent answer is here: http://stackoverflow.com/a/454413/66686 — Jens Schauder, Apr 17 '12 at 18:39

NPE · Accepted Answer · 2012-04-17T17:18:17.103

14

This programming convention has been around for a long time, and probably goes back all the way to Fortran. In Fortran 77, variables beginning with the letters I, J, K, L, M, or N were taken to be of type INTEGER (unless explicitly declared otherwise). That made them very well suited to be loop variables.

Of course i, j etc have been used in maths to denote matrix/vector/summation indices for much, much longer than computers have existed.

edited Apr 17 '12 at 17:18

answered Apr 17 '12 at 17:12

NPE

464,258
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and the fact that i & j are used for indexes in math is probably the reason for the Fortran convention. – Jens Schauder Apr 17 '12 at 18:16
@Jens Schauder: absolutely correct :) – paulsm4 Jun 19 '12 at 20:03

score 3 · Answer 2 · answered Apr 17 '12 at 17:12

3

Simple variable names that are easy to read. Also it dates back to the C days in K+R

answered Apr 17 '12 at 17:12

SeanPONeil

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score 3 · Answer 3 · answered Apr 17 '12 at 17:12

3

I think it is a habit that finds it simple origin in the fact that i is the first letter of integer and index.

answered Apr 17 '12 at 17:12

Martijn Courteaux

65,802
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score 3 · Answer 4 · answered Apr 17 '12 at 17:15

i and j are commonly used in linear algebra when doing matrix multiplication and summations. i is conveniently short for index. and j is lexicographically adjacent to i.

Now that it's so established, I wouldn't use anything else, lest the programming gods bring pain upon ye.

MAC · Answer 5 · 2012-04-17T17:31:32.913

3

i stands for index j comes after i..

so its easy to remember and handle

that's why we are using in sequence i,j,k,l.....

edited Apr 17 '12 at 17:31

answered Apr 17 '12 at 17:22

MAC

15,659
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score 2 · Answer 6 · answered Apr 17 '12 at 17:16

2

i, and j are also used in math and physics. i is often the notation for Cartesian x-axis basis unit vector while j is used for Cartesian y-axis basis unit vector.

answered Apr 17 '12 at 17:16

wachpwnski

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Java- Why for uses i,j

6 Answers6