Addition de 2 entiers java

String entier;
	
	public static String addition(String s1,String s2)
	{
	    int retenu=0;
		String resultat="";
		int ent1 ;
		int ent2;
		int i=s2.length()-1;
			if(s1.length()>s2.length() && i>0)
			{
				for(int k=s1.length()-1;k>=s1.length()-s2.length();k-- )
				{
				 ent1 = Integer.parseInt(s1.charAt(k)+"");
				 ent2= Integer.parseInt(s2.charAt(i)+"");
				 i--;
				int somme=ent1+ent2;
				 if(somme>=10)
				{
				retenu=1;
				resultat=somme-10+retenu+""+resultat;
				}
				else 
					resultat=somme+""+resultat;
			    }
				 for(int j=s1.length()-s2.length()-1;j>=0;j--)
					resultat=s1.charAt(j)+""+resultat;
			}
		return resultat;
	}
	  public static void main(String[] args)
	  {
			String s1="1232434534634673";
			String s2="13972324";
			
			String s=addition(s1,s2);
			
			System.out.println(s);	  
	  }