/**
 *  testing for byte-int conversion 
 *  what is intended to demonstrate is:
 *           (int)((byte)0x81) != (int)0x81
 */
public class test{
    
    public static void main(String[] args)
    {
    	// indentity conversion(int->int): 
        //      0x00000081 --> j1=129 ( two's complement value)
    	int j1 = 0x81;  
    	System.out.println();
    	System.out.println("(int)0x81 = " + Integer.toString(j1)); // (int)0x81 = 129
    	System.out.println(j1 + "&0xFF --> " + Integer.toString(j1&0xFF)); // 129&0xFF --> 129
    	System.out.println(j1 + "&0xFFFFFFFF --> " + Integer.toString(j1&0xFFFFFFFF)); // 129&0xFFFFFFFF --> 129
    	
    	// narrowing conversion(int->byte): 
        //     0x00000081(129) -> 10000001(-127) --> b1=-127 ( two's complement value)
    	// where the sign of 0x00000081 gets lost! 
    	byte b1 = (byte)0x81;  
    	System.out.println();
    	System.out.println("(byte)0x81 = " + Integer.toString(b1)); // (byte)0x81 = -127
    	System.out.println(b1 + "&0xFF --> " + Integer.toString(b1&0xFF)); // -127&0xFF --> 129
    	System.out.println(b1 + "&0xFFFFFFFF --> " + Integer.toString(b1&0xFFFFFFFF)); // -127&0xFFFFFFFF --> -127
    	
    	// widening conversion(byte->int): 
        //          10000001(-127) -> 0xffffff81(-127)
    	// where the sign and magnitude get both perserved
    	int j2 = b1;  
    	System.out.println();
    	System.out.println("(int)((byte)0x81) --> 0x" + Integer.toHexString(j2)); // (int)((byte)0x81) --> 0xffffff81
    	System.out.println("(int)((byte)0x81) = " + Integer.toString(j2)); // (int)((byte)0x81) = -127
    	System.out.println(j2 + "&0xFF --> " + Integer.toString(j2&0xFF)); // -127&0xFF --> 129
    	System.out.println(j2 + "&0xFFFFFFFF --> " + Integer.toString(j2&0xFFFFFFFF)); // -127&0xFFFFFFFF --> -127
    	
    	String comment = "So, be very careful while handling data of byte, " +
		                 "particularly byte-int conversion. For example, \n" + 
						 "            (byte)0x81 != (int)0x81 \n" +
						 "     (int)((byte)0x81) != 0x81 \n" +
						 " but \n" +
						 "      ((byte)0x81)&0xFF == ((int)0x81)&0xFF";
    	System.out.println();
    	System.out.println(comment);
    	
    }
}