How to fix both Found 'DD'-anomaly and only one return statement - pmd

Question

I have some difficulties when fixing PMD warnings, this was my simplified method:
public String rank(String keyword, int pageSize, int totalPage)
{
String result = "0"; // A: DataflowAnomalyAnalysis: Found 'DD'-anomaly for variable 'result'
if (isNotBlank(keyword))
{
boolean find = false; // B: DataflowAnomalyAnalysis: Found 'DD'-anomaly for variable 'find'
for (int page = 1; page < totalPage; page++)
{
int rank = getRank(keyword, pageSize, totalPage);
if (rank != 0)
{
find = true; // B(1)
result = String.valueOf(rank); // A(1)
break;
}
}
if (!find)
{
result = format("{0}+", totalPage * pageSize - 1); // A(2)
}
}
return result;
}
I tried this and got "OnlyOneReturn" warnings:
public String rank(String keyword, int pageSize, int totalPage)
{
if (isNotBlank(keyword))
{
for (int page = 1; page < totalPage; page++)
{
int rank = getRank(keyword, pageSize, totalPage);
if (rank != 0)
{
return String.valueOf(rank); // OnlyOneReturn
}
}
return format("{0}+", totalPage * pageSize - 1); // OnlyOneReturn
}
return "0";
}
How do I have to write this code please?

Answer 1

A 'DD'-anomaly an a dataflow analysis tells you that you assign a variable more than once without using it between the assignments. So all but the last assignment are unnecessary. It usually indicates that you didn't separate your scenarios properly. In your case you have three scenarios:
If the keyword is blank then the return value is "0".
Otherwise loop through all pages and if getRank() returns a rank other than zero then this is the return value.
Otherwise the return value is "totalPage * pageSize - 1+"
If you implement those scenarios one by one you end up with a method that has not any dataflow or other PMD issues:
public String rank(String keyword, int pageSize, int totalPage) {
String result;
if (isNotBlank(keyword)) {
result = "0";
} else {
int rank = 0;
for (int page = 1; page < totalPage && rank == 0; page++) {
rank = getRank(keyword, pageSize, totalPage);
}
if (rank != 0) {
result = String.valueOf(rank);
} else {
result = format("{0}+", totalPage * pageSize - 1);
}
}
return result;
}
If you take a closer look at the for loop you see that page is only used for looping. It is not used inside the loop. This indicates that the for loop is probably not necessary. getRank(keyword, pageSize, totalPage) should always return the same value as its arguments never change during the loop. So it might be enough to call getRank(...) just once.