How to avoid null checking in Java?

Question

I use object != null a lot to avoid NullPointerException.

Is there a good alternative to this?

For example I often use:

Answer 1

If null-values are not allowed

If your method is called externally, start with something like this:

public void method(Object object) {
  if (object == null) {
    throw new IllegalArgumentException("...");
  }

Then, in the rest of that method, you'll know that object is not null.

If it is an internal method (not part of an API), just document that it cannot be null, and that's it.

Example:

public String getFirst3Chars(String text) {
  return text.subString(0, 3);
}

However, if your method just passes the value on, and the next method passes it on etc. it could get problematic. In that case you may want to check the argument as above.

If null is allowed

This really depends. If find that I often do something like this:

if (object == null) {
  // something
} else {
  // something else
}

So I branch, and do two completely different things. There is no ugly code snippet, because I really need to do two different things depending on the data. For example, should I work on the input, or should I calculate a good default value?

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It's actually rare for me to use the idiom "if (object != null && ...".

It may be easier to give you examples, if you show examples of where you typically use the idiom.