Why can't I use the ternary ? operator to select between two function calls?

Question

I was recently programming and ran into an issue using the ? : operand. Here's my code.

    Random rand = new Random();
    for(int x = 0; x < 3; x++) {
        rand.nextInt(1) == 0 ? vertShip(board) : horizShip(board);
    }

My compiler throws me an error stating that the left hand side of the line (rand.nextInt(1) == 0 ) must be a variable. I've tried variants such as

    Random rand = new Random();
    int a = rand.nextInt(1);
    for(int x = 0; x < 3; x++) {
        a == 0 ? vertShip(board) : horizShip(board);
    }

or if statements in the left hand side but they don't fix the problem. Would anyone be able to help me?

Answer 1

Not every expression is a statement. Use an if statement here. See Section 14.8 Expression Statements in the Java SE 7 Java Language Specification.

Certain kinds of expressions may be used as statements by following them with semicolons.

 ExpressionStatement: StatementExpression ; StatementExpression: Assignment PreIncrementExpression PreDecrementExpression PostIncrementExpression PostDecrementExpression MethodInvocation ClassInstanceCreationExpression 

Examples of expression statement for each of the above:

x = y;
++x;
--x
x++;
x--;
fn(); // Or donkey.fn();, etc.
new Donkey(this);

What you can't do is:

b ? f() : g();
f() + g();

However, if you're dead set on obfuscating your code, I guess you could write:

fn(a == 0 ? vertShip(board) : horizShip(board));
(a == 0 ? vertShip(board) : horizShip(board)).fn();

(I think. I don't have a compiler to hand and wouldn't usually write such code.)

Answer 2

The compiler is right. The ternary operator returns something, so you need to assign it to a variable.

Answer 3

Java isn't perl. Use an if statement:

 if (rand.nextInt(1) == 0) {
    vertShip(board);
 } else { 
    horizShip(board);
 }

You can't build a function call statement by sticking the ternary ? on the front.

Answer 4

a == 0 ? vertShip(board) : horizShip(board); // is an expression
if (a == 0) vertShip(board); else horizShip(board); // is a statement

Compare:

if (condition) 
{
    execute statement(s)
}
else
{
    execute statement(s)
}

With:

 expression1 ? expression2 : expression3 

Use the appropriate construct.