// create a mask of 1s 24 bits wide.
int mask24 = 0xffffff;
// or
int mask24 = ( 1 << 24 ) - 1;  // watch out, formula does not work for 32

// create a mask of 0s 24 bits wide, the rest 1s
int mask024 = 0xff000000;
// or
int mask024 = ~0xffffff;
// or
int mask024 = ~( ( 1 << 24 ) - 1 );  // watch out, formula does not work for 32

// create a mask of ones to extract the second lowest byte
int mask2 = 0x0000ff00;
// or
int mask2 = ( ( 1 << 8 ) - 1 ) >>> 8;

// create  mask for clearing the second lowest byte
int clear2 = 0xffff00ff;
// or
int clear2 = ~(( ( 1 << 8 ) - 1 ) >>> 8 );

// use it to clear that byte and leave everything else alone with
int v &= clear2;