How to Handle NullPointerException in LinkedList When Using a For-Each Loop

What causes NullPointerException in a LinkedList when iterating with a for-each loop?

List<String> list = null;
for (String item : list) {
    System.out.println(item);
}

A NullPointerException in a LinkedList during iteration with a for-each loop indicates that the list is not properly initialized. This exception occurs when the code tries to iterate over an object that is null instead of a valid collection.

// Example of initializing and checking for null
LinkedList<String> list = new LinkedList<>(); // Properly initialize your LinkedList
list.add("First");
list.add("Second");

// Iterate safely
for (String item : list) {
    System.out.println(item);
}

Causes

• The LinkedList has not been initialized (set to null).
• The LinkedList was cleared or not properly assigned before the for-each loop is called.
• Using a method that returns a null LinkedList.

Solutions

• Ensure that the LinkedList is initialized before using it. For example, use `LinkedList<String> list = new LinkedList<>();`.
• Check the source of the LinkedList and ensure that it is not null before the iteration begins.
• If the LinkedList can be null, consider using an if-statement to prevent iteration: `if (list != null) { ... }`.

Mistake: Neglecting to check if the LinkedList is initialized before usage.

Solution: Always initialize the LinkedList or check for null before the for-each loop.

Mistake: Clearing the list inadvertently and trying to iterate after that.

Solution: Ensure that the list has elements before iteration.