Java Ternary Operator insert != null check and syso not printed

Question

I have two questions. First

int i = 0;
System.out.println("\nint i is" + (i == 0) ? "i==0" : "i!=0");

I receive this error: Type mismatch: cannot convert from String to boolean
Eclipse tells me
1 quick fix available: Insert != null check

Second

System.out.println("\nint i is" + (i == 0) != null ? "i==0" : "i!=0");

With the != null check I get no error, but "\nint i is" is not printed, only the result i==0. I totally not understand the errors. Please help =)

Answer 1

You need to parenthesize your conditional expression properly:

System.out.println("\nint i is" + ((i == 0) ? "i==0" : "i!=0"));

Otherwise, + is executed before applying the conditional, so the conditional is parsed as follows:

"\nint i is" + (i == 0) ? "i==0" : "i!=0"
-----------------------   ------   ------
             |              |         |
Condition ---+              |         |
When the condition is true -+         |
When the condition is false ----------+

"\nint i is" + (i == 0) is a valid Java expression that produces a string, triggering the "need a Boolean" error.