Friday, October 30, 2015

short circuit operator in java

class BoolArray 
{
    boolean [] b = new boolean[3];
    int count = 0;

    void set(boolean [] x, int i) 
    {
        x[i] = true;
        ++count;
    }

    public static void main(String [] args) 
    {
        BoolArray ba = new BoolArray();
        ba.set(ba.b, 0);
        ba.set(ba.b, 2);
        ba.test();
    }

    void test() 
    {
        if ( b[0] && b[1] | b[2] )
            count++;
        if ( b[1] && b[(++count - 2)] )
            count += 7;
        System.out.println("count = " + count);
    }
}


Result count = 3

Why?

The reference variables b and x both refer to the same boolean array. count is incremented for each call to the set() method, and once again when the first if test istrue. Because of the && short circuit operator, count is not incremented during the second if test.

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