在 Java 中切换布尔变量的最简洁方法？

Question

Is there a better way to negate a boolean in Java than a simple if-else?

if (theBoolean) {
    theBoolean = false;
} else {
    theBoolean = true;
}

Answer 1

theBoolean = !theBoolean;

Answer 2

theBoolean ^= true;

Fewer keystrokes if your variable is longer than four letters

Edit : code tends to return useful results when used as Google search terms. The code above doesn't. For those who need it, it's bitwise XOR as described here .

Answer 3

There are several

The "obvious" way (for most people)

theBoolean = !theBoolean;

The "shortest" way (most of the time)

theBoolean ^= true;

The "most visual" way (most uncertainly)

theBoolean = theBoolean ? false : true;

Extra: Toggle and use in a method call

theMethod( theBoolean ^= true );

Since the assignment operator always returns what has been assigned, this will toggle the value via the bitwise operator, and then return the newly assigned value to be used in the method call.

Answer 4

This answer came up when searching for "java invert boolean function". The example below will prevent certain static analysis tools from failing builds due to branching logic. This is useful if you need to invert a boolean and haven't built out comprehensive unit tests ;)

Boolean.valueOf(aBool).equals(false)

or alternatively:

Boolean.FALSE.equals(aBool)

or

Boolean.FALSE::equals

Answer 5

If you use Boolean NULL values and consider them false, try this:

static public boolean toggle(Boolean aBoolean) {
    if (aBoolean == null) return true;
    else return !aBoolean;
}

If you are not handing Boolean NULL values, try this:

static public boolean toggle(boolean aBoolean) {
   return !aBoolean;
}

These are the cleanest because they show the intent in the method signature, are easier to read compared to the ! operator, and can be easily debugged.

Usage

boolean bTrue = true
boolean bFalse = false
boolean bNull = null

toggle(bTrue) // == false
toggle(bFalse) // == true
toggle(bNull) // == true

Of course, if you use Groovy or a language that allows extension methods, you can register an extension and simply do:

Boolean b = false
b = b.toggle() // == true

Answer 6

The class BooleanUtils supportes the negation of a boolean. You find this class in commons-lang:commons-lang

BooleanUtils.negate(theBoolean)

Answer 7

If you're not doing anything particularly professional you can always use a Util class. Ex, a util class from a project for a class.

public class Util {


public Util() {}
public boolean flip(boolean bool) { return !bool; }
public void sop(String str) { System.out.println(str); }

}

then just create a Util object Util u = new Util(); and have something for the return System.out.println( u.flip(bool) );

If you're gonna end up using the same thing over and over, use a method, and especially if it's across projects, make a Util class. Dunno what the industry standard is however. (Experienced programmers feel free to correct me)

Answer 8

Unfortunately, there is no short form like numbers have increment/decrement:

i++;

I would like to have similar short expression to invert a boolean, dmth like:

isEmpty!;

Answer 9

Before:

boolean result = isresult();
if (result) {
    result = false;
} else {
    result = true;
}

After:

boolean result = isresult();
result ^= true;