**
 * To be used by “getCourseName”, “getCourseId”, and “getStudentId” methods.  
 * 
 * Gets the String that follows the line that starts with the given String. 
 * Gets and returns the String on the very next line.
 * If the given String doesn't exist, should return null.
 * 
 * Example(s):
 * - If an ArrayList<String> lines contains: "hello" and "world", and we call 
 * getNextStringStartsWith("hello"), we'll get the String "world".
 * 
 * - If an ArrayList<String> lines contains: "Course" and "CIT590", and we call 
 * getNextStringStartsWith("Course"), we'll get the String "CIT590".
 * 
 * - If an ArrayList<String> lines contains: "hello" and "world", and we call 
 * getNextStringStartsWith("goodbye"), we'll get null.
 * 
 * @param str to look for in lines
 * @return String from the very next line

how to fix java.util.NoSuchElementException on my code, here is my code:

private ArrayList<String> lines = new ArrayList<String>();

public InfoProcessor(ArrayList<String> lines) {
    this.lines = lines;
}

String getNextStringStartsWith(String str) {
    
    // TODO Implement method
    
    Iterator<String> it = lines.iterator();

    if (!lines.contains(str)) return null;
        
    while (it.hasNext() && !it.next().equals(str)) {
        it.next();
    }

    return it.next();        
}

If an ArrayList lines contains: "hello" and "world", and we call getNextStringStartsWith("goodbye"), we'll get null. I tried to use !lines.contains(str), but it does not work, can anyone help me with this, thank you!

CodePudding user response：

I have tried implementing the method getNextStringStartsWith using contains method, it does not return any error. I have shown the implementation below.

private static String getNextStringStartsWith(String str) {
    if (lines.contains(str)) {
        int res = lines.indexOf(str);
        return lines.get(res 1);
    }
    
    return null; 
}

Also, i'm assuming if the last element ( say "world") is passed in the example, then output will be null only as it the last element of the list.

CodePudding user response：

If the matched String is the last element in your list, of course you get NoSuchElementException because the iterator already reached the end.

A simple fix would be change return it.next(); to return it.hasNext() ? it.next() : null; But there are other "problems" in your code.

1. Normally, you declare variables using the interface(List), instead of a specific implementation(ArrayList).
2. the Big O of contains in List is O(n), you actually looped the list twice.
3. no null handling

Below is my version of code

private List<String> lines = new ArrayList<>();

public InfoProcessor(List<String> lines) {
    this.lines = lines;
}

String getNextStringStartsWith(String str) {
    for (int i = 0; i < lines.size(); i  ) {
        String current = lines.get(i);
        boolean matched = false;

        if (Objects.isNull(str)) {
            if (Objects.isNull(current)) {
                matched = true;
            }
        } else if (str.equals(lines.get(i))) {
            matched = true;
        }

        if (matched && i < lines.size() - 1) {
            return lines.get(i   1);
        }
    }

    return null;
}