Question

Can someone explain the question mark in the following code? Also INITIAL_PERMANCE is a static final constant in the code but what is the last line of synatax called?

Synapse(AbstractCell inputSource, float permanence) {
    _inputSource = inputSource;
    _permanence = permanence==0.0 ? 
        INITIAL_PERMANENCE : (float)Math.min(1.0,permanence);
}

Answer 1

The ? and : are part of the java conditional operator. Sometimes called the ternary operator because it is the only operator in Java that takes 3 arguments.

This is essentially an inline IF / THEN / ELSE block.

_permanence = permanence==0.0 ? 
    INITIAL_PERMANENCE : (float)Math.min(1.0,permanence);

Can be rewritten as follows:

if (permanence == 0.0)
    _permanence = INITIAL_PERMANENCE;
else
    _permanence = (float) Math.min(1.0,permanence);

The general form of the conditional operator is

<Test returning a boolean> ? <value for if test is true> : <value for if test is false>