Java 7 - Null-ignore invocation

Have you ever had an NPE in production? Or felt that handling null is a right pain? Well perhaps this Java 7 language change proposal - Null-ignore invocation - will interest you.

The concept is to provide the developer with a tool to handle null, that will reduce NPEs and improve code clarity. To explain this, lets consider this method:

  public String getPostcode(Person person) {
    return person.getAddress().getPostcode()
  }

The problem is that this code may throw an NPE if person or getAddress() is null. Here is the 'correct' way to code this:

  public String getPostcode(Person person) {
    if (person != null) {
      Address address = person.getAddress();
      if (address != null) {
        return address.getPostcode();
      }
    }
    return null;
  }

The problem with the 'correct' solution is that the intent of the code has been lost. The null-checks are really getting in the way of reading and understanding the method.

This proposal aims to tackle this by adding compiler syntax sugar to generate the null pointer checks for developers. It achieves this by adding an alternative to the dot for method and field invocation, the hash - #. Using the hash invokes a method or field in the same way as using the dot, but with one change. If the expression on the left hand side of the hash is null, then the result of the expression is null. If the expression type is a primitive then zero or false is returned instead of null. If the expression is a void, then no action occurs.

  public String getPostcode(Person person) {
    return person#getAddress()#getPostcode()
  }

This code is now null-safe and won't throw an NPE. (Of course the interals of getAddress() or getPostcode() might throw NPE.) In addition the code is now back to its former clarity - you can now read it and clearly see the intent without any visual clutter.

I know that some reading this will cry 'Null object design pattern'. Well maybe thats fine in your closed sourcebase, where you can enforce its use with code reviews and so on. But as soon as your code deals with an external library, or even the JDK, then your code has to handle null. Which leads you right back to this proposal.

If you want to read the full details, I've written up the formal Null-ignore invocation proposal. If you've got any suggested enhancements or fixes to the proposal, let me know. All feedback welcomed.