Question

I have a List of books and I want to do a case insensitive search of the book titles, to see if they contain a particular string. This string might be present as a word or a part of a word. My method keeps returning a null pointer exception...

Answer 1

```
private List<Book> books;

private String search(String searchWord) {
List<Book> searchResult = null;
for(Book b : books) {
boolean check = books.stream().filter(o -> b.getTitle().equals(searchWord)).findFirst().isPresent();
if (check = true) {
searchResult.add(b);
}
else return searchWord + " not found";
}
return buildResult(searchResult);
}
```
Why is it that my searchResult list remains empty even after I am adding to it?

Answer 2

I do think that there is something wrong with my Boolean check...I think...but I can't seem to figure out what

Answer 3

It seems searchResult isn't initialized. Without creating the object by calling it's constructor, the list object wont really exist, nor will it have access to it's non-static methods or it's non-static field variables.

Though List can't be initialized by doing new List<Book>(); because it's an interface:
http://stackoverflow.com/questions/13395114/how-to-initialize-liststring-object-in-java
Though you can initialize it to any of the classes that implement the List interface; my personal favorite is the ArrayList class.
`List<Book> searchResult = new ArrayList<Book>();`

I'm not sure what most of the method calls in your check do, though I'll add that I think the `String.contains()` method is a good way to test whether a String contains a certain CharSequence or not.
```
String s = "sSsffff 33";
System.out.println(s.contains("ss")); //false
System.out.println(s.contains("ff 3")); //true
```

Answer 4

Thank you, well that...and a few other tweaks resulted in a method that now works :) The `else` part of the if-statement needed modification and the state of the Boolean 'check' needed to be returned to `false` for each iteration.

```
private String search(String searchWord) {
List<Book> searchResult = new ArrayList<Book>();
int notFound = 0;
for(Book b : books) {
boolean check = false;
check = b.getTitle().trim().toLowerCase().contains(searchWord.toLowerCase());
if (check != false) {
searchResult.add(b);
}
else notFound++;
}
if (notFound == books.size()){
return "The word you are looking for, could not be found";
}
return buildResult(searchResult);
}

Answer 5

Looks clean, glad I could help :)