Gracefully avoiding NullPointerException in Java

Question

Consider this line:

if (object.getAttribute(\"someAttr\").equals(\"true\")) { // ....

Obviously this line is a potential bug, the attribute

Answer 1

There are certain situations where the concise approach feels wrong to start with but effectively becomes idiomatic. This is one of them; the other is something like:

String line;
while ((line = bufferedReader.readLine()) != null) {
  // Use line
}

Side effects in a condition? Unthinkable! Except it's basically nicer than the alternatives, when you recognise the particular pattern.

This pattern is similar - it's so common in Java that I'd expect any reasonably experienced developer to recognise it. The result is pleasantly concise. (Amusingly, I sometimes see C# code which uses the same idiom, unnecessarily - the equality operator works fine with strings in C#.)

Bottom line: use the first version, and become familiar with it.

Answer 2

I've always used

if ("true".equals(object.getAttribute("someAttr"))) { // ....

because although it is a little more difficult to read it's much less verbose and I think it's readable enough so you get used to it very easily

Answer 3

I have another answer;

List<Map<String, Object>> group = jjDatabase.separateRow(db.Select("SELECT * FROM access_user_group  WHERE user_id=1 ;"));

there is not "group_c80" as column in 'access_user_group' in my database, so in get(0).get("group_c80") null pointer exception accords. But i handled it through below code :

for (int j = 1; j < 100; j++) {
                    String rulId="0";//defult value,to privent null pointer exeption in group_c
                    try {
                        rulId = group.get(0).get("group_c" + j)).toString();
                    } catch (Exception ex) {
                        ServerLog.Print( "Handeled error in database for " + "group_c" + (j < 10 ? "0" + j : j) +"This error handeled and mot efect in program");
                        rulId = "0";
                    }}