java.lang.NullPointerException: Cannot invoke "String.length()" because "<local1>" is null — how to fix

Exception in thread "main" java.lang.NullPointerException: Cannot invoke "String.length()" because "name" is null
	at com.example.App.greet(App.java:12)
	at com.example.App.main(App.java:5)

Quick fix: Read the helpful message (because "x" is null) and the first at line in your code. Find where that value should have been set: an uninitialized field, a map/repository lookup that returned null, a missing injection, or an unboxed null Integer. Fix it at the source, or handle absence explicitly with Objects.requireNonNull, Optional, or a null check.

What it means

You used null as if it were an object. Since JDK 14 (default on since 15), helpful NullPointerException messages say what was null:

• Cannot invoke "String.length()" because "name" is null
• Cannot read field "address" because "user" is null
• Cannot load from int array because "arr" is null
• Cannot invoke "java.lang.Integer.intValue()" because ... is null (unboxing)

If the message says "<local1>" instead of a variable name, the class was compiled without debug info; compile with javac -g (Maven/Gradle do this by default) to see names.

The first at line pointing to your package is where it happened. On older JDKs with no message, split chained calls across lines so the line number tells you which part was null.

Cause 1: an uninitialized field

class Cart {
    private List<Item> items;           // null
    void add(Item i) { items.add(i); }  // NPE
}

Initialise at declaration or in the constructor:

private final List<Item> items = new ArrayList<>();

Cause 2: a lookup returned null

Map.get, HttpServletRequest.getParameter, System.getenv, Class.getResource, many DAO methods and JSON libraries return null when something isn't there.

String port = System.getenv("PORT");
int p = Integer.parseInt(port);               // NumberFormatException: null, or NPE later

Handle the absent case:

int p = Integer.parseInt(System.getenv().getOrDefault("PORT", "8080"));

User u = repo.findById(id)                    // Optional<User> in Spring Data
             .orElseThrow(() -> new NotFoundException(id));

Cause 3: auto-unboxing a null wrapper

Map<String, Integer> counts = new HashMap<>();
int c = counts.get("x");          // get returns null -> NPE on intValue()

Use counts.getOrDefault("x", 0), or keep the type as Integer and check it. The same happens with Boolean fields from JSON/DB in if (user.getActive()). Use Boolean.TRUE.equals(user.getActive()).

Cause 4: Spring/DI didn't inject the field

@Autowired fields are null when:

• you created the object yourself with new MyService() instead of letting Spring create it;
• the class isn't a bean (@Component/@Service missing, or outside the component-scan package);
• you use the field in a constructor (field injection happens after construction).

Prefer constructor injection, which fails at startup instead of with an NPE later:

@Service
class OrderService {
    private final PaymentClient client;
    OrderService(PaymentClient client) { this.client = client; }
}

Cause 5: string comparisons and equals on a null

status.equals("ACTIVE") throws if status is null. Put the constant first or use Objects.equals:

"ACTIVE".equals(status);
Objects.equals(a, b);

switch on a null String or enum also throws an NPE.

Cause 6: arrays and collections containing null

new String[10] holds ten nulls until you fill it. List.of(...) and Map.of(...) reject nulls with an NPE at creation, and ConcurrentHashMap rejects null keys/values.

Prevent it

• Validate inputs early: this.name = Objects.requireNonNull(name, "name");
• Return empty collections or Optional instead of null.
• Use nullness annotations (@Nullable, @NonNull) with IntelliJ inspections, Error Prone/NullAway or SpotBugs to catch NPEs at compile time.

Last updated 2026-11-05.