Base 10 to base 2

class DecToBin
{
 public static void main(String[] args)
 {
 //System.out.println("Hello World!");
 long dec = -9223372036854775807l;
 // -9223372036854775808  This number is not good, don't try, hey hey
 String binStr="";
 long decAbs=Math.abs(dec);
 while (decAbs>0)
 { binStr=(decAbs&1)+binStr;
 decAbs>>=1;
 }
 binStr= dec<0?"-"+binStr:dec==0?"0":binStr;

 System.out.println(binStr);
 }
}

Decimal to decimal

class DecToOct
{
 public static void main(String[] args)
 {
 //System.out.println("Hello World!");
 long dec=-0;// There are -0  ?
 String octStr="";
 long decAbs=Math.abs(dec);
 while (decAbs>0)
 { octStr=(decAbs&7)+octStr;//
 decAbs>>=3;
 }
 octStr= dec<0?"-"+octStr:dec==0?"0":octStr;
 System.out.println(octStr);
 }
}

Decimal to decimal

class DecToHex
{
 public static void main(String[] args)
 {
 System.out.println("Hello World!");
 long dec=-1;// You don't get negative Numbers on your calculator  - . -
 String hexStr="";
 long decAbs=Math.abs(dec);
 while(decAbs>0)
 { long lastFour=decAbs&15;
 if (lastFour>9)
 hexStr=(char)('A'+lastFour-10)+hexStr;
 else hexStr=lastFour+hexStr;
 decAbs>>=4;
 }
 hexStr= dec<0?"-"+hexStr:dec==0?"0":hexStr;
 System.out.println(hexStr);
 }
}