Only 5 of 1000 can trace this Java assignment-precedence brain-twister

Description

The image has a black background with white text. The top caption reads, "Uni stats says only 5 students out of 1k able to answer right:". Below that, a white code panel shows the exact Java snippet: public static void main(String[] args) { int a=9,b=4,c=7,d=1,e=3; while ((a=1)==1 && (b=2)==3 && (c=3)==3 || (d=4)==4 || (e=5)==7) { System.out.println(a + " " + b + " " + c + " " + d + " " + e); break; } } The joke relies on hidden assignments inside the while-condition and Java's operator-precedence/short-circuit rules, causing the loop to print "1 2 7 4 3" despite the initial values. It pokes fun at how few students (or interviewees) remember that `=` returns a value, `&&` binds tighter than `||`, and evaluation stops once an `&&` chain hits false

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Java LanguageQuirks CodingChallenge CSFundamentals Interview

Comments

Anonymous ★ Top Pick Seeing while((a=1)==1 && (b=2)==3 …) in a code review is that special moment you realize operator precedence isn’t the bug - someone just packed side-effects, job security, and a subtle “I quit” into one boolean

Anonymous ★ Top Pick

Seeing while((a=1)==1 && (b=2)==3 …) in a code review is that special moment you realize operator precedence isn’t the bug - someone just packed side-effects, job security, and a subtle “I quit” into one boolean
Anonymous

After 20 years of code reviews, I've learned that the difference between = and == in conditionals is what separates those who debug production incidents at 3am from those who cause them. Though honestly, any codebase that makes it past review with assignments in conditionals probably has bigger architectural problems than operator confusion
Anonymous

Ah yes, the classic 'assignment masquerading as comparison' interview hazing ritual. This is the kind of code that makes you appreciate why modern linters scream at you for assignments in conditionals. The real answer? Only 5 out of 1000 students got it right because the other 995 had already learned to write maintainable code and refused to engage with this production-ready nightmare on principle. If you unironically write conditions like this, your PR reviews must be absolutely *chef's kiss* brutal
Anonymous

1 & 2 = 0: bitwise AND's polite way of saying 'loop over, no println invited'
Anonymous

Prints 1 2 7 4 3 exactly once - also known as the mandatory code‑review where we enable a linter and ban assignment in conditionals forever
Anonymous

It prints “1 2 7 4 3” once - short-circuit assignments set a,b,d and skip c,e; academia calls it a clever exam question, production calls it a postmortem
@sylfn 3y

1 2 3 4 5 ?
@cthulhu_dev 3y

1 2 3 4 3
@pointan 3y

1 2 7 4 3
@affirvega 3y

Nothing
@grandpa_the_kid 3y

5 is assigned to e and then it is compared to 7, so how can it go into the while body?
1. @CCZeroOne 3y
  
  there's OR
Vitalik 3y

1 2 7 4 3
@trainzman 3y

Should it even show anything
1. @callofvoid0 3y
  
  doesn't that continue to after or ?
  
  @trainzman 3y
  
  https://en.wikipedia.org/wiki/Short-circuit_evaluation
  
  @trainzman 3y
  
  Then, If we account both this
2. @M4lenov 3y
  
  No this part makes the program not execute the rest of monominal (c=3) and skips to the d=4 part
  
  @trainzman 3y
  
  I talked about it lower
3. @scout_ca11sign 3y
  
  Yes && Has bigger priority than || Think of it as multiplying first and summing later a*b*c + d + e _ a*b*c = 0 d = 1 e = 0 _ 0 + 1 +0 = 1
@Similacrest 3y

1 2 3 4 3
@mold_in 3y

6 9 1 4 8 8
@lab0rat 3y

1 2 7 4 3
@grandpa_the_kid 3y

oh, jeez, realy)
@CCZeroOne 3y

)
@realVitShadyTV 3y

1 2 7 4 3
@callofvoid0 3y

12743
@CCZeroOne 3y

it's probably 12743, but I can also see it being 12343, if it's a trick question, and the third one gets evaluated, cuz there's something after it
@trainzman 3y

I guess Java uses it
@trainzman 3y

It won't print anything anyway
@trainzman 3y

Because && has less priority than || iirc
1. @sylfn 3y
  
  AND has greater priority than OR
  
  @trainzman 3y
  
  And this
2. @callofvoid0 3y
  
  I thought it reads from left to right without propority
  
  @trainzman 3y
  
  It doesn't
@Samurhai 3y

12743?
@trainzman 3y

It should give 12743
@trainzman 3y

They always have different priorities
@CCZeroOne 3y

alright it is 12743
@CCZeroOne 3y

I checked
Егор 3y

it’s 1 2 7 4 3 obviously, but RIGHT answer is «i don’t care»
@callofvoid0 3y

seems like whole left hand part of first || is counted as a block
1. @beton_kruglosu_totchno 3y
  
  no it's not
2. Егор 3y
  
  it stops processing ANDs when finds first false and stops processing ORs when it finds first true
  
  @callofvoid0 3y
  
  ah thanks
  
  @callofvoid0 3y
  
  resulted exactly as this
3. @beton_kruglosu_totchno 3y
  
  AND and OR have same precedence
@callofvoid0 3y

let me change position of and,or and see what happens
@DavidGarciaCat 3y

infinite loop?
1. @dst212 3y
  
  break; doesn't agree
  
  @DavidGarciaCat 3y
  
  Yeah, I ran a quick investigation later and I know now my both guessings were wrong
@DavidGarciaCat 3y

or maybe syntax error?
dev_meme 3y

The real answer to this is refactoring 😂👀
@realbond007 3y

a=1 (first assignment) | 1==1 : true, continue condition evaluation b=2 (second assignment) | 2==3 : false, short circuit break (AND FALSE operation), therefore all following && will be ignored c=7 (initial value remains - see comment above) d=4 (third assignment) | 4==4 : true, short circuit break (OR TRUE operation), therefore all following || will be ignored e=3 (initial value remains - see comment above) therefore 1 2 7 4 3 🤓
@Iliya_malecki 3y

1 2 7 4 5 piss easy

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Only 5 of 1000 can trace this Java assignment-precedence brain-twister

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