java中比较未知字符串所包好的内容

public static int[][] LCS(String str1, String str2) {
int[][] opt = new int[str2.length() + 1][str1.length() + 1];

    for (int i = 0; i <= str2.length(); i++) {
        opt[i][0] = 0;
    }

    for (int j = 0; j <= str1.length(); j++) {
        opt[0][j] = 0;
    }

    for (int j = 1; j <= str1.length(); j++) {
        for (int i = 1; i <= str2.length(); i++) {
            if (str2.charAt(i-1) == str1.charAt(j-1)) {
                opt[i][j] = opt[i-1][j-1] + 1;
            } else {
                opt[i][j] = ( opt[i-1][j] >= opt[i][j-1] ? opt[i-1][j] : opt[i][j-1]);
            }
        }
    }

    return opt;
}

public static void print(int[][] opt, String X, String Y, int i, int j) {

    if (i == 0 || j == 0) {
        return;
    }

    if (X.charAt(i - 1) == Y.charAt(j - 1)) {
                   System.out.print(X.charAt(i - 1));   
                   print(opt, X, Y, i - 1, j - 1);  // don't put this line before the upper line. Otherwise, the order is wrong.
            }else if (opt[i - 1][j] >= opt[i][j]) {
                   print(opt, X, Y, i - 1, j);
            } else {
                   print(opt, X, Y, i, j - 1);}
}