example.java

public class BinaryConverter {
 
 public static void main(String[] args){
 for(int i = -5; i < 33; i++){
 System.out.println(i + ": " + toBinary(i));
 System.out.println(i);
 //always another way
 System.out.println(i + ": " + Integer.toBinaryString(i));
 }
 }
 
 /*
 * pre: none
 * post: returns a String with base10Num in base 2
 */
 public static String toBinary(int base10Num){
 boolean isNeg = base10Num < 0;
 base10Num = Math.abs(base10Num); 
 String result = "";
 
 while(base10Num > 1){
 result = (base10Num % 2) + result;
 base10Num /= 2;
 }
 assert base10Num == 0 || base10Num == 1 : "value is not <= 1: " + base10Num;
 
 result = base10Num + result;
 assert all0sAnd1s(result);
 
 if( isNeg )
 result = "-" + result;
 return result;
 }
 
 /*
 * pre: cal != null
 * post: return true if val consists only of characters 1 and 0, false otherwise
 */
 public static boolean all0sAnd1s(String val){
 assert val != null : "Failed precondition all0sAnd1s. parameter cannot be null";
 boolean all = true;
 int i = 0;
 char c;
 
 while(all && i < val.length()){
 c = val.charAt(i);
 all = c == '0' || c == '1';
 i++;
 }
 return all;
 }
}