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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.

Answer 1

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;
}