Is >>>= Broken?

[Darrin Cartwright]

Or am I just missing something.
When I try to use the "right shift with zero extension" operator, I still get 1's filling in from the left.
Can anyone tell me what I am doing wrong?
Here is a little sample program:

  
public class testBits {

    public testBits() {
    }
    
    // Creates a string representing the bits in num
    public String getBits( short num )
    {
        String bitString = "";
        // create mask
        short mask = 1;  // 00000000 00000001
        mask <<= 15;     // 10000000 00000000
        
        for( int i = 1; i <= 16; i++ )
        {
            if( (num & mask) == 0 )
                bitString += "0";
            else
                bitString += "1";
            // shift one left
            num <<= 1;
            // add seperator every 8 bits
            if( i % 8 == 0 )
                bitString += " ";
        }
        
        return bitString;
    }
    
    public static void main(String[] args) {
        
        testBits test = new testBits();
        short num = 1;
        System.out.println("1 bits are : " + test.getBits( num ) );
        num <<= 3;
        System.out.println("Shift left 3 (num <<= 3) : " + test.getBits( num ) );
        num >>= 3;
        System.out.println("Shift right three (num >>= 3) : " + test.getBits( num ) );
        num <<= 15;
        System.out.println("Put one at end (num <<= 15) : " + test.getBits( num ) );
        num >>= 7;
        System.out.println("Shift right seven with sign extension (num >>= 7) : " + test.getBits( num ) );
        num <<= 7;
        System.out.println("Put one at end (num <<= 7) : " + test.getBits( num ) );
        num >>>= 7;
        System.out.println("Now shift right seven WITHOUT sign extension (num >>>= 7) : " + test.getBits( num ) );
        System.out.println("Huh? What happened. 00000001 00000000 was expected!");
    }
}

On the next to last line of this program I would expect 00000001 00000000 to be printed.
Please help. The cattle are restless.

[Wirianto Djunaidi]

The reason is >>>= operate on int data type, so your number got converted
into int during shift and you got the erroneous result when it was truncated back. If you had used

num = num >>> 7;

You'll see the compiler give a warning regarding the lost of precision.
If you change your data type to int, it will show the correct result.
[ September 29, 2003: Message edited by: Wirianto Djunaidi ]