Checking the “boolean” result of an “int” type

问题

I'm learning Java, coming from C and I found an interesting difference between languages with the boolean type. In C there is no bool/ean so we need to use numeric types to represent boolean logic (0 == false).

I guess in Java that doesn't work:

int i = 1;
if (i)
    System.out.println("i is true");

Nor does changing the conditional via a typecast:

if ((boolean)i)

So besides doing something like:

if ( i != 0 )

Is there any other way to do a C-ish logic check on an int type? Just wondering if there were any Java tricks that allow boolean logic on non-boolean types like this.

EDIT:
The example above was very simplistic and yields itself to a narrow scope of thinking. When I asked the question originally I was thinking about non-boolean returns from function calls as well. For example the Linux fork() call. It doesn't return an int per se, but I could use the numeric return value for a conditional nicely as in:

if( fork() ) {
    // do child code

This allows me to process the code in the conditional for the child, while not doing so for the parent (or in case of negative return result for an error).

So I don't know enough Java to give a good "Java" example at the moment, but that was my original intent.

回答1:

In Java,

if ( i != 0 )

is the idiomatic way to check whether the integer i differs from zero.

If i is used as a flag, it should be of type boolean and not of type int.

回答2:

Why not use the boolean type ? That will work as you expect without the potentially problematic integer/boolean conflation.

private boolean isValid;
...
if (!isValid) {
   ...
}

Note that this is the idiomatic Java approach. 3rd party libs use this, and consumers of your API will use and expect it too. I would expect libs that you use to give you booleans, and as such it's just you treating ints as booleans.

回答3:

FROM JLS:

The boolean type has two values, represented by the boolean literals true and false, formed from ASCII letters.

Thus no is the answer. the only was is

if ( i != 0 )

回答4:

Try BooleanUtils from Apache common-lang.

  BooleanUtils.toBoolean(0) = Boolean.FALSE
  BooleanUtils.toBoolean(1) = Boolean.TRUE
  BooleanUtils.toBoolean(2) = Boolean.TRUE

回答5:

In java the condition has to be of type boolean else it can't be an expression, that is why

if( i )

is not allowed.

It has to be either true or false.

回答6:

You could try something like that. Boolean i = true; if (i) System.out.println("i is true");

Just initialize it as a boolean value rather than an integer.

回答7:

If you insist to use int instead of boolean, just use a method to convert

class BooleanHelper
{
   public static boolean toBoolean (int pVal) {
      return pVal != 0;
   }
 ...
}

// apply

if (BooleanHelper.toBoolean(i)) { // BooleanHelper could be avoided using static imports...

However, just use