java Example of generating bit masks with "ones" one the left or on the right // ((1<<x)-1) // (-1<<x)

TestBitMask.java

public class TestBitMask {

	public static void main(String[] args) throws Exception{
		System.out.println("Java integer bit mask example");
		
		System.out.println();
		System.out.println("Zeroes on the left and x ones on the right. Formula: ((1<<x)-1)");
		for(int x=1; x<32;x++) {
			System.out.println(x+"\t "+padRight(  ((1<<x)-1)  ,12) +""+intBitsSpaced(((1<<x)-1)));
		}
		
		System.out.println();
		System.out.println("Zeroes on the right and x ones on the left. Formula: (-1<<x) ");
		for(int x=1; x<32;x++) {
			System.out.println(x+"\t "+padRight(  (-1<<x)     ,12) +""+intBitsSpaced(((1<<x)-1)));
		}
	}

	private static String padRight(int i, int count) {
		StringBuffer buffer = new StringBuffer().append(i);
		while(buffer.length() < count) buffer.append(' ');
		return buffer.toString();
	}	

	public static String intBitsSpaced(int val) {
		StringBuffer b = new StringBuffer(37);// 32 bits + 3 spaces
		for(int i=31;i>=0; i--) {
			b.append((val & (1<<i)) == 0 ? '0':'1');
			if(i>0 && i%8 ==0) b.append(' ');
		}
		return b.toString();
	}    


}
/*
Zeroes on the left and x ones on the right. Formula: ((1<<x)-1)
1	 1           00000000 00000000 00000000 00000001
2	 3           00000000 00000000 00000000 00000011
3	 7           00000000 00000000 00000000 00000111
4	 15          00000000 00000000 00000000 00001111
5	 31          00000000 00000000 00000000 00011111
6	 63          00000000 00000000 00000000 00111111
7	 127         00000000 00000000 00000000 01111111
8	 255         00000000 00000000 00000000 11111111
9	 511         00000000 00000000 00000001 11111111
10	 1023        00000000 00000000 00000011 11111111
11	 2047        00000000 00000000 00000111 11111111
12	 4095        00000000 00000000 00001111 11111111
13	 8191        00000000 00000000 00011111 11111111
14	 16383       00000000 00000000 00111111 11111111
15	 32767       00000000 00000000 01111111 11111111
16	 65535       00000000 00000000 11111111 11111111
17	 131071      00000000 00000001 11111111 11111111
18	 262143      00000000 00000011 11111111 11111111
19	 524287      00000000 00000111 11111111 11111111
20	 1048575     00000000 00001111 11111111 11111111
21	 2097151     00000000 00011111 11111111 11111111
22	 4194303     00000000 00111111 11111111 11111111
23	 8388607     00000000 01111111 11111111 11111111
24	 16777215    00000000 11111111 11111111 11111111
25	 33554431    00000001 11111111 11111111 11111111
26	 67108863    00000011 11111111 11111111 11111111
27	 134217727   00000111 11111111 11111111 11111111
28	 268435455   00001111 11111111 11111111 11111111
29	 536870911   00011111 11111111 11111111 11111111
30	 1073741823  00111111 11111111 11111111 11111111
31	 2147483647  01111111 11111111 11111111 11111111

Zeroes on the right and x ones on the left. Formula: (-1<<x) 
1	 -2          11111111 11111111 11111111 11111110
2	 -4          11111111 11111111 11111111 11111100
3	 -8          11111111 11111111 11111111 11111000
4	 -16         11111111 11111111 11111111 11110000
5	 -32         11111111 11111111 11111111 11100000
6	 -64         11111111 11111111 11111111 11000000
7	 -128        11111111 11111111 11111111 10000000
8	 -256        11111111 11111111 11111111 00000000
9	 -512        11111111 11111111 11111110 00000000
10	 -1024       11111111 11111111 11111100 00000000
11	 -2048       11111111 11111111 11111000 00000000
12	 -4096       11111111 11111111 11110000 00000000
13	 -8192       11111111 11111111 11100000 00000000
14	 -16384      11111111 11111111 11000000 00000000
15	 -32768      11111111 11111111 10000000 00000000
16	 -65536      11111111 11111111 00000000 00000000
17	 -131072     11111111 11111110 00000000 00000000
18	 -262144     11111111 11111100 00000000 00000000
19	 -524288     11111111 11111000 00000000 00000000
20	 -1048576    11111111 11110000 00000000 00000000
21	 -2097152    11111111 11100000 00000000 00000000
22	 -4194304    11111111 11000000 00000000 00000000
23	 -8388608    11111111 10000000 00000000 00000000
24	 -16777216   11111111 00000000 00000000 00000000
25	 -33554432   11111110 00000000 00000000 00000000
26	 -67108864   11111100 00000000 00000000 00000000
27	 -134217728  11111000 00000000 00000000 00000000
28	 -268435456  11110000 00000000 00000000 00000000
29	 -536870912  11100000 00000000 00000000 00000000
30	 -1073741824 11000000 00000000 00000000 00000000
31	 -2147483648 10000000 00000000 00000000 00000000

*/