1 class  DecToBin
 2 {
 3     public static void main(String[] args) 
 4     {
 5         //System.out.println("Hello World!");
 6         long dec = -9223372036854775807l;
 7                 // -9223372036854775808 这个数不行，不要试，嘿嘿
 8         String binStr="";
 9         long decAbs=Math.abs(dec);
10         while (decAbs>0)
11         {    binStr=(decAbs&1)+binStr;
12             decAbs>>=1;
13         }
14         binStr= dec<0?"-"+binStr:dec==0?"0":binStr;
15 
16         System.out.println(binStr);
17     }
18 }

 1 class  DecToOct
 2 {
 3     public static void main(String[] args) 
 4     {
 5         //System.out.println("Hello World!");
 6         long dec=-0;//有-0 吗？
 7         String octStr="";
 8         long decAbs=Math.abs(dec);
 9         while (decAbs>0)
10         {    octStr=(decAbs&7)+octStr;//
11             decAbs>>=3;
12         }
13         octStr= dec<0?"-"+octStr:dec==0?"0":octStr;
14         System.out.println(octStr);
15     }
16 }

 1 class DecToHex
 2 {
 3     public static void main(String[] args) 
 4     {
 5         System.out.println("Hello World!");
 6         long dec=-1;//计算器的负数不会弄 -。-
 7         String hexStr="";
 8 
 9         long decAbs=Math.abs(dec);
10         while(decAbs>0)
11         {    long lastFour=decAbs&15;
12             if (lastFour>9)
13             hexStr=(char)(‘A‘+lastFour-10)+hexStr;
14             else hexStr=lastFour+hexStr;
15             decAbs>>=4;
16         }
17 
18         hexStr= dec<0?"-"+hexStr:dec==0?"0":hexStr;
19         System.out.println(hexStr);
20     }
21 }