Optional.of(null)will throw NPE, I need to verify null before call the method?

Question

Java 8 introduces Optional to deal with NPE. In practical application，I can‘t understand a problem.

I have the method A

public void doSomethingA(String para) {
    Optional<String> name = Optional.of(para);
    if (name.isPresent()) {
        //do
    }
}

But if para = null, it will throw NPE.

method B

public void doSomethingB(String para) {
    if (para != null) {
        //do
    }
}

if I check para is not null, What's the difference between A and B.

Where is the meaning of Optional.

Answer 1

Use Optional.ofNullable if you are unsure whether you have a value or not, but you do not want a NullPointerException to be thrown.

Use Optional.of if you know you have a non-null-value or if it's ok for you if a NullPointerException is thrown otherwise.

Regarding the rest of your question: why null or Optional you may find the following question useful: Optional vs. null. What is the purpose of Optional in Java 8?

Your question may also be related to: Why use Optional.of over Optional.ofNullable?

Answer 2

Optional does not prevent from throwing an NPE, It makes it very easy to avoid, but you have to do your part, for example, I would refactor your code to something like this.

     public void doSomethingA(String para) {
           
           Optional<String> optName = Optional.ofNullable(para);
        
           String name = optName.orElse("Unknown");
    //At his point, you are completely sure that name is even given name or "Unknown" 
    //and can do wherever you want without being afraid of throwing a NPE
    
        }

You can use other optional Method like: optName.orElseThrow() to throw and error if your param is null, optName.orElseGet(() -> { return "Unknown" ;}); practically does the same than the example but you can add more logic to get the default value, or many other methods.