How to avoid NullPointerException
java.lang.NullPointerException
When can it be thrown?
According to the JavaDoc, the following scenarios can be found.
- Calling the instance method of a null object.
- Accessing or modifying the field of a null object.
- Taking the length of null as if it were an array.
- Accessing or modifying the slots of null as if it were an array.
- Throwing null as if it were a Throwable value.
How to avoid it?
- Use Optional in Java 8
- Call equals() and equalsIgnoreCase() methods on known objects.
- Use valueOf() over toString()
public class NullCheckDemo {
public static void main(String args[]){
Integer i = null;
System.out.println(i.toString()); //This throws NullPointerException
System.out.println(String.valueOf(i)); //This returns null
}
}
- Use null-safe methods and libraries. Ex: Apache Commons StringUtils.
- Use @NotNull and @Nullable annotations
- Always check for nulls.
public class NullDemo {
public static void main(String args[]){
Integer i = null;
if(i != null)
System.out.println(i);
else
System.out.println("error occurred");
}
}
