如何使用if / else快捷方式根据布尔值打印字符串

Question

I would like to print:

Permissive mode: ON

or

Permissive mode: OFF

I was trying to do it in one line like this:

       logMessage("Permissive mode: " +  (isPermissive == true) ? "ON" : "OFF" );

I could do full if/else statement and a separate variable for ON/OFF but was trying to keep it short...

Answer 1

只需使用

logMessage("Permissive mode: " +  ((isPermissive) ? "ON" : "OFF"));

Answer 2

You need parentheses around the conditional assignment operator ? : ? : because there's an addition operator before it, and + has a higher precedence than ? : ? : .

Without the parentheses, "Permissive mode: " + (isPermissive == true) ? "ON" : "OFF" "Permissive mode: " + (isPermissive == true) ? "ON" : "OFF"

is equivalent to ("Permissive mode: " + (isPermissive == true)) ? "ON" : "OFF" ("Permissive mode: " + (isPermissive == true)) ? "ON" : "OFF"

The result of the + addition operator with String operands isn't a boolean , so the compiler will complain rightfully on the expression.

You need to surround the operator with less precedence with parentheses if you want it to evaluate first:

logMessage("Permissive mode: " +  (isPermissive ? "ON" : "OFF") );

Answer 3

You can factorize it with a new method, wrapping logMessage:

public void myLogMessage(String message, boolean flag) {
    logMessage(message + ": " + (flag ? "ON" : "OFF"));
}