Java statements: Obfuscated code - `?:`

Question

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What is the Java ?: operator called and what does it do?

I am trying to read an implementation of a binary tree, and I ran across this one line of code:

if (...) {
   ...
} else {
    node = ( node.left != null ) ? node.left : node.right;    //this line
}

return node;

Can anyone tell me what this line means? My best guess is that it's a conditional statement of some kind.

Rohit Jain · Accepted Answer · 2012-11-17T09:04:38.453

9

It is called Conditional Operator.

In expression1 ? expression2: expression3, the expression1 returns a boolean value. If it is true then expression2 is evaluated, else expression3 is evaluated.

So in your code snippet: -

node = ( node.left != null ) ? node.left : node.right;

is equivalent to: -

if (node.left != null) {
    node = node.left;
} else {
    node = node.right;
}

edited Nov 17 '12 at 09:04

answered Nov 16 '12 at 04:50

Rohit Jain

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Great! Thanks for the help, and thanks again for the if-then translation as well! – Nov 16 '12 at 04:54
2

expression1 and expression2 would be better than statement1 and statement2. – Bhesh Gurung Nov 16 '12 at 04:55

score 3 · Answer 2 · answered Nov 16 '12 at 04:52

This is known as the ternary operator, since in most languages it's the only operator which takes 3 arguments. It has the form:

a ? b : c

and evalutes to b if a is true, or c otherwise. It can be used almost anywhere, but most frequently it is used in assignment operations, since it becomes very difficult to read in more complex situations.

On a side note, "obfuscated" is not the right term here - that is meant for code which is deliberately rendered difficult to read. This might more accurately be called "obscure", although it is a common operator.

Java statements: Obfuscated code - `?:`

2 Answers2