Java operators ":" "?"

Question

I'm not completely sure how to use the operators : and ?

Example: I have this code in the end of a method

return row <= -1 || row == rows || col <= -1 || col == cols ? 
            false : lifeBoard[row][col];

How would I split it up in to if/else types?

Java does not have those operators. It has the single `?:` operator. — Sotirios Delimanolis, Nov 26 '14 at 16:09
See https://docs.oracle.com/javase/tutorial/java/nutsandbolts/op2.html — Jon Skeet, Nov 26 '14 at 16:11
That whole expression could be written as an `||`, though, FWIW. — Louis Wasserman, Nov 26 '14 at 16:14
What you are looking at is the [Ternary Conditional Operator](https://en.wikipedia.org/wiki/%3F%3a). — AlvinJ, Nov 26 '14 at 16:14
Possible duplicate of [What is the Java ?: operator called and what does it do?](https://stackoverflow.com/questions/798545/what-is-the-java-operator-called-and-what-does-it-do) — domsson, Jul 24 '17 at 12:46

score 6 · Accepted Answer · answered Nov 26 '14 at 16:12

?: (the ternary operator) works as a a compact if-else:

if (row <= -1 || row == rows || col <= -1 || col == cols) {
        return false;
}
else {
    return lifeBoard[row][col];
}

Whatever comes before the ? is the condition, between ? and : comes the result if the condition is true, and after : comes the result if the condition is false.

Pokechu22 · Answer 2 · 2014-11-26T16:18:09.793

This:

return row <= -1 || row == rows || col <= -1 || col == cols ? 
            false : lifeBoard[row][col];

Is equivalent to this:

if (row <= -1 || row == rows || col <= -1 || col == cols) {
    return false;
} else {
    return lifeBoard[row][col];
}

The syntax of the Ternary operator ?: is this:

Statement to evaluate ? Value if true : Value if false

It is like if/else but it can be used inside of a return statement or similar:

return (x != null ? x : "null");

score 2 · Answer 3 · answered Nov 26 '14 at 16:11

2

If/else version:

if (row <= -1 || row == rows || col <= -1 || col == cols) {
    return false;
} else {
    return lifeBoard[row][col];
}

answered Nov 26 '14 at 16:11

Egor Neliuba

14,784
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score 2 · Answer 4 · answered Nov 26 '14 at 16:12

2

This is the syntax:

<boolean expression> ? <value if true> : <value if false>

Example

boolean myBool = getMyBool();
String myStr = myBol ? "myBol is true" : "myBol is false";
System.out.println(myStr);

answered Nov 26 '14 at 16:12

Predrag Maric

23,938
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score 2 · Answer 5 · answered Nov 26 '14 at 16:12

2

This is a ternary operation. So for example

minVal = (a < b) ? a : b;

Would be the same as

if(a < b) {
    minVal = a;
}
else {
    minVal = b;
}

answered Nov 26 '14 at 16:12

Jeremy W

1,889
6
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Shubham Soin · Answer 6 · 2014-12-04T18:20:18.283

It is a Conditional operator also known as Ternary operator. It is simply the compact form of if else statement wherein you don't have to use if and else separately.

Here's how it works...

"?"- anything written before the"?" is the condition

":"- anything written before the ":" is chosen as the result if the condition mentioned before "?" is true

anything written after the ":" is chosen as the result if the condition mentioned before "?" is false

This is how it works...

So splitting the given code into if/else can be easily done as follows -

    if (row <= -1 || row == rows || col <= -1 || col == cols) {
        return false;
    }
    else {
        return lifeBoard[row][col];
    }

Java operators ":" "?"

6 Answers6