Java Ternary without Assignment

问题

Is there a way to do a java ternary operation without doing an assignment or way to fake the assingment?

I like how succinct ternary code looks when doing a bunch of if/then/elses.

I\'m hoping to be able to call one of two void functions based on a boolean algebra statement.

Something like:

(bool1 && bool2) ? voidFunc1() : voidFunc2();

My functions are of return type void, so if there is a way to fake this in an assignment to make it work, then I\"m okay with that... I would like to see how to do it though :)

回答1:

Nope you cannot do that. The spec says so.

The conditional operator has three operand expressions. ? appears between the first and second expressions, and : appears between the second and third expressions.

The first expression must be of type boolean or Boolean, or a compile-time error occurs.

It is a compile-time error for either the second or the third operand expression to be an invocation of a void method.

[EDIT]

Since you asked about reflection, here's a solution. I'm not recommending this. I'm posting it only because you asked.

public class MyCall
{

    public void a(){System.out.println("a");}
    public void b(){System.out.println("b");}

    public static void main(String... args)
    {
        new MyCall().go();
    }

    public void go()
    {
        Class<? extends MyCall> class1 = this.getClass();
        Method aMethod = class1.getMethod("b", null);
        Method bMethod = class1.getMethod("a", null);
        Object fake = false ? aMethod.invoke(this, null) : bMethod.invoke(this, null);
        Object fake2 = true ? aMethod.invoke(this, null) : bMethod.invoke(this, null);
    }
}

At the end of the day you've got to ask yourself if being succint improves your code's readability (think for-each loop). None of these solutions improve the code's readability IMHO. If I were you I'd rather go with this.

if(condition)
    a();
else
    b();

I'm actually for including braces even when loops only contain a single line, but since you're going after crisp code, the snippet above should do.

回答2:

No, you can't do this like this.

You can prefer this style if do not like make it more statements.

if(bool1 && bool2) voidFunc1(); else voidFunc2();

In ternary operator, Operands are required to be non-void expressions; i.e. they must produce some actual value.

回答3:

If you really-really want to use ternany operation, then there is one hack. BUT this is very bad code, intended only for showing abilities of language. I would never recommend to put this code in production or even show to your friends.

int dummy = (bool1 && bool2) ? new Object(){
        public int hashCode() {
            yourFunction1();
            // ...
            yourFunctionN();
            return 0;
        };
    }.hashCode() : new Object(){
        public int hashCode() {
            yourAnotherFunction1();
            // ...
            yourAnotherFunctionN();
            return 0;
        };
    }.hashCode();

回答4:

Is there a way to do a java ternary operation without doing an assignment or way to fake the assignment?

OK, so when you write a statement like this:

    (bool1 && bool2) ? voidFunc1() : voidFunc2();

there are two distinct problems with the code:

The 2nd and 3rd operands of a conditional expression¹ cannot be calls to void methods. Reference: JLS 15.25.
An expression is not a statement, unless it is either and assignment expression OR a method call OR a object creation. Reference: JLS 14.8.

In fact, the second of these problems is a syntax error and I would expect any mainstream Java compilers to report it instead of the first problem. The first problem would only reveal itself if you did something like this:

    SomeType dummy = (bool1 && bool2) ? voidFunc1() : voidFunc2();

    gobble((bool1 && bool2) ? voidFunc1() : voidFunc2());

where gobble is a method that does nothing ... except "consume" the value of its argument.

AFAIK, there is no context in which the original expression is acceptable.

^{1 - "Conditional expression" is the primary term used for this construct in the Java Language Specification. It is called the "ternary conditional operator" in Oracle Java Tutorial.}

来源：https://stackoverflow.com/questions/15977031/java-ternary-without-assignment

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java

ternary-operator

ternary