[java] What is a stack trace, and how can I use it to debug my application errors?

To add on to what Rob has mentioned. Setting break points in your application allows for the step-by-step processing of the stack. This enables the developer to use the debugger to see at what exact point the method is doing something that was unanticipated.

Since Rob has used the NullPointerException (NPE) to illustrate something common, we can help to remove this issue in the following manner:

if we have a method that takes parameters such as: void (String firstName)

In our code we would want to evaluate that firstName contains a value, we would do this like so: if(firstName == null || firstName.equals("")) return;

The above prevents us from using firstName as an unsafe parameter. Therefore by doing null checks before processing we can help to ensure that our code will run properly. To expand on an example that utilizes an object with methods we can look here:

if(dog == null || dog.firstName == null) return;

The above is the proper order to check for nulls, we start with the base object, dog in this case, and then begin walking down the tree of possibilities to make sure everything is valid before processing. If the order were reversed a NPE could potentially be thrown and our program would crash.

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