glog_td4/questioncomplementaire/Cesar.java

package questioncomplementaire;

public class Cesar extends AlgoCodage{
	private int decalage;
	private String alphabet = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";

	public Cesar(int decalage){
		this.nom = "César";
		this.decalage = decalage;
	}
	
	@Override
	public String toString() {
		return "codage de César (décalage=" + decalage + ")"; 
	}

	@Override
	public String encode(String s) {
		String encode = "";
		for(int i=0;i<s.length();i++){
			encode += alphabet.charAt((decalage +
						alphabet.indexOf(s.charAt(i)))%alphabet.length());
		}
		return encode;
	}

	@Override
	public String decode(String s) {
		String decode = "";
		int index;
		for(int i=0; i<s.length(); i++) {
			index = (alphabet.indexOf(s.charAt(i))-decalage) % alphabet.length();
			index += (index<0)?alphabet.length():0;
			decode += alphabet.charAt(index);
		}
		return decode;
	}
}