Adding big numbers using Strings in java

BigNumberAdd.java

public String Add(String input1, String input2) {  
	String ans = "";
	int len1 = input1.length();
	int len2 = input2.length();

	if(len1 < len2){
		String temp = input1; 
		input1 = input2; 
		input2 = temp; 
	}

	len1 = input1.length();
	len2 = input2.length();

	int diff = len1 - len2;

	int c = 0;
	for(int i=len1 - 1, j=len2 - 1; j>=0 ; i--, j--) {
		int sum = Character.getNumericValue(input2.charAt(j)) + Character.getNumericValue(input1.charAt(i)) + c;
		c = (int)sum/10;
		sum%=10;
		ans = String.valueOf(sum) + ans;
	}

	for(int i = diff - 1; i>=0; i--) {
		int sum = Character.getNumericValue(input1.charAt(i)) + c;
		c = (int)sum/10;
		sum%=10;
		ans = String.valueOf(sum) + ans;
	}
		
	if(diff == 0) {
		ans = String.valueOf(c) + ans;
	}
	
	if(c != 0) {
        	ans = String.valueOf(c) + ans;
    	}

	int i = 0; 
        while (ans.charAt(i) == '0' &&  i<ans.length()-1) 
            i++;

        StringBuffer sb = new StringBuffer(ans); 
		if(i == ans.length())
			return "0";
		
        sb.replace(0, i, ""); 
  
	return sb.toString();
  }