如果else陈述无法正常运作

Question

af, ae, and be are all integers and here I am checking to see if they equal 0. If not, I want to return null. If they do equal zero, I want to return glorpPoly. For some reason though, it always returns null even when the condition is satisfied... does anyone know why? all these values are of a type our teacher created called MyDouble. all of them have been initialized to this value, but it still doesn't work.

MyDouble af = a.multiply(poly.c);
    MyDouble ae = a.multiply(poly.b);
    MyDouble bf = b.multiply(poly.c);
    MyDouble cf = c.multiply(poly.c);
    MyDouble be = b.multiply(poly.b);
    MyDouble ad = a.multiply(poly.a);
    MyDouble ce = c.multiply(poly.b);
    MyDouble bd = b.multiply(poly.c);
    MyDouble cd = c.multiply(poly.a);
    //Adding the the variables and creating new coefficients
    MyDouble newA = af;
    MyDouble newB = ae.add(bf);
    MyDouble newC = cf.add(be).add(ad);
    MyDouble newD = ce.add(bd);
    MyDouble newE = cd;
    MyDouble zero = new MyDouble(0)
if(af != zero && ae !=zero && be != zero){

        return null;
    }
    else{
        MartianPolynomial glorpPoly = new MartianPolynomial(newC,newD,newE);
        return glorpPoly;
    }
}

Answer 1

Objects can't be compared using == or != . You have to use the equals() method:

if (!af.equals(zero) && !ae.equals(zero) && !be.equals(zero) {
  ...
}

The operators != and ( == ) check for object identity, ie if both references point to the same instance. They don't compare the "value" of the instances.

Answer 2

LE: if 'af','ae' and 'be' are numbers (type int,double,float) you can use:

if(af != 0 && ae !=0 && be != 0)

but if they are objects, you can either compare their attributes by 0 or compare them with an object of the same type.See: http://msdn.microsoft.com/en-us/library/bsc2ak47.aspx

Answer 3

怎么样

if(! af.equals(zero) && ! ae.equals(zero) && ! be.equals(zero) ) ...

Answer 4

If you are checking if they are all zero, just multiply them all together and if the result is zero, well you know...

I am assuming, since you did not provide your MyDouble class, that you have a method of retrieving the value ?

if ((af.value() * ae.value() * be.value()) != 0)

OP , please provide us with your MyDouble.java class.