Convertir les bases dans le système de numération

Salut,

J'en pense que ça ne sert pas à grand chose, puisqu'il suffit de faire Integer.toString(Integer.parseInt(number, from),to), avec from la base de départ, et to la base d'arrivée.
Et aussi qu'on peut faire beaucoup plus simple, si on veut (ou doit) absolument le faire soi-même :
Code:
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public class ConversionBase {
 
	public static String convertJava(String number, int from, int to) {
		return Integer.toString(Integer.parseInt(number, from),to);
	}
 
	public static String convert(String number, int from, int to) {
		Objects.requireNonNull(number,"Number must be not null");
		return convert(convert(number, from),to);
	}
 
	public static int convert(String number, int radix) {
		Objects.requireNonNull(number,"Number must be not null");
		if ( radix<Character.MIN_RADIX || radix>Character.MAX_RADIX ) {
			throw new NumberFormatException("Illegal radix: " + radix);
		} 
		boolean minus=false;
		if ( number.trim().isEmpty() ) {
			throw new NumberFormatException("For input string: \"" + number + "\"");
		}
		else if ( number.startsWith("-")) {
			minus = true;
			number = number.substring(1);
		}
		int result=0;
		int pow=1;
		final char[] chars=number.toCharArray();
		for(int i=chars.length-1; i>=0; i--) { 
			if (pow<=0) throw new NumberFormatException("For input string: \"" + number + "\"");
			final int value = valueOf(number, chars[i]);
			if ( value<radix ) {
				result+=value*pow;
			}
			else {
				throw new NumberFormatException("For input string: \"" + number + "\"");
			}
			pow*=radix;
		}
		return minus?-result:result;
	}
 
	private final static int MAX_DIGIT_10=(int)Math.log(Integer.MAX_VALUE)+1;
	public static String convert(int number, int radix) {
		if ( radix<Character.MIN_RADIX || radix>Character.MAX_RADIX ) {
			throw new NumberFormatException("Illegal radix: " + radix);
		}
		boolean minus=false;
		if ( number==0 ) {
			return "0";
		}
		else if ( number<0 ) {
			minus=true;
			number=-number;
		}
		final StringBuilder stringBuilder=new StringBuilder(MAX_DIGIT_10+(minus?1:0)); 
		while(number>0) {
			stringBuilder.insert(0, valueOf(number%radix));
			number/=radix;
		} 
		if ( minus ) {
			stringBuilder.insert(0,'-');
		}
		return stringBuilder.toString();
	}
 
	private static int valueOf(String number, char c) {
		if ( '0'<=c && c<='9') {
			return c-'0';
		}
		else {
			c = Character.toLowerCase(c);
			if ( c>='a' && c<='z' ) {
				return 10+c-'a';
			}
			else {
				throw new NumberFormatException("For input string: \"" + number + "\"");
			}
		}
	}
 
	private static char valueOf(int c) {
		if ( 0<=c && c<=9) {
			return (char)('0'+c);
		}
		else {
			return (char)('a'+(c-10));
		}
	}
 
	public static void main(String[] args) {
		test("123",10,2);
		test("123",8,2);
		test("123",10,10);
		test("123",4,10); 
		test("1111111111111111111111111111111",2,10);
		test("FF01",16,2);
		test("abcd",16,10);
		test("abcd",20,10);
		test("-42",10,4);
		test("-42",10,2);
	}
 
	private static void test(String number, int from, int to) {
		System.out.println("Convert "+number+" from " + from + " to " + to +":");
		System.out.println("Java: " + convertJava(number, from, to));
		System.out.println("Self: " + convert(number, from, to));
	}
 
}