Hackforge Academy

Explanation

What is NullPointerException? In Java, null means the reference is not pointing to any object. If you try to use a null reference, Java throws: java.lang.NullPointerException

Code:

Explanation

Basic Null Check
Without Null Check String name = null; System.out.println(name.length());

Code:

With Null Check
String name = null;
if (name != null) {
  System.out.println(name.length());
} else {
    System.out.println("Name is null");
}

Explanation

Using Ternary Operator

Code:

String name = null;

int length = (name != null) ? name.length() : 0;

System.out.println(length);

Explanation

Using Objects Class (Java 7+) Java provides Objects utility class. Objects.requireNonNull() Throws custom error if null.

Code:

import java.util.Objects;

String name = null;
Objects.requireNonNull(name, "Name cannot be null");
Output:
Exception: Name cannot be null

Explanation

Objects.isNull() and Objects.nonNull()

Code:

import java.util.Objects;

String name = null;

if (Objects.isNull(name)) {
    System.out.println("Name is null");
}

Explanation

Using Optional (Java 8+) Optional helps avoid direct null handling.

Code:

import java.util.Optional;

String name = null;

Optional<String> optionalName = Optional.ofNullable(name);

optionalName.orElse("Default Name");
//Default Name

Explanation

With ifPresent()

Code:

Optional<String> optionalName = 
Optional.ofNullable("hackforge");

optionalName.ifPresent(n -> 
System.out.println(n));

Explanation

Using Java 14+ Objects.requireNonNullElse()

Code:

import java.util.Objects;


String name = null;


String result = Objects.requireNonNullElse(name, "Default");

System.out.println(result);

Explanation

Code:

1.Always validate method parameters

2.Use Optional for return types (not for fields)

3.Use constant-first string comparison

4.Avoid returning null — return empty list instead