Question about "null" intepretations

Hi people,

sorry i have a question which might be stupid but i want to clarify something. For my DB interface i have the following statement:

// Returns an array of record numbers that match the specified
// criteria. Field n in the database file is described by
// criteria[n]. A null value in criteria[n] matches any field
// value. A non-null value in criteria[n] matches any field
// value that begins with criteria[n]. (For example, "Fred"
// matches "Fred" or "Freddy".)
public int[] find(String[] criteria);

does a null value in can be null or "" or it only refers to null?

null is null in my opinion. Empty is something completely different.

Benjamin,
Refer to Roberto Buddy's test. He uses String[] criteria = {"Palace", "Smallvile", null, null, null, null, null} to test his find algorithm. I believe our assignment should have null pointer exception handling in this case.

Hi Benjamin

If you read the comments carefully you should have realized that "null" indicates a wildcard.

thanks for the reply everyone. Now i doing junit testing on the find method for the Data.java and i need some clarification. If my criteria array is all empty value which means is {"","","","","",""}, what should the expected result for the find method? 0 records or all valid record in the database?

0 records.
Because all records have their names and cities. Their names and cities are not "".

Himai Minh wrote:0 records.
Because all records have their names and cities. Their names and cities are not "".

how about i pass in a String array of {null,null,"","","",""}, is the expected result still 0?

In my find-method passing an array containing all null-values will result in all valid records being returned. If an array is passed with non-null values the null values are simply ignored.

Benjamin Ng wrote:

Himai Minh wrote:0 records.
Because all records have their names and cities. Their names and cities are not "".

how about i pass in a String array of {null,null,"","","",""}, is the expected result still 0?

The expected result is all records. K Tsang buddy said null indicates a wildcard. The first "null" indicates all records with any name. The second null indicates all records with any city.

If you have a string array of {null, "New York", null, null, null, null}. The expected result is any name in New York city.

Himai Minh wrote:

Benjamin Ng wrote:

Himai Minh wrote:0 records.
Because all records have their names and cities. Their names and cities are not "".

how about i pass in a String array of {null,null,"","","",""}, is the expected result still 0?

The expected result is all records. K Tsang buddy said null indicates a wildcard. The first "null" indicates all records with any name. The second null indicates all records with any city.

If you have a string array of {null, "New York", null, null, null, null}. The expected result is any name in New York city.

Sorry i am getting confused. Let me clarify something, based on my understanding, if i send a String array of {null,null,"","","",""}, shouldn't the expected result is 0 because even though both name and location are using null, but the rest of the search is not using wildcard so the check should be something like <is the rate begins with "">, <is the size begins with "">, <is the owner begins with ""> which for these cases they are not begin with "" so the final results is return 0 records?

Hi Benjamin buddy,
Agree. This is confusing.
You may want to assume "" is a value. For example, name is "".
If the name criteria is "", search for names "".
If the name criteria is null, return all records with any name.

Agree with this ?

Himai Minh wrote:Hi Benjamin buddy,
Agree. This is confusing.
You may want to assume "" is a value. For example, name is "".
If the name criteria is "", search for names "".
If the name criteria is null, return all records with any name.

Agree with this ?

Yes i agreed.