Should a retrieval method return 'null' or throw an exception when it can't produce the return value? [closed]

Answer 1

As a general rule, if the method should always return an object, then go with the exception. If you anticipate the occasional null and want to handle it in a certain way, go with the null.

Whatever you do, I highly advise against the third option: Returning a string that says "WTF".

Answer 2

Use the null object pattern or throw an exception.

Answer 3

Just ask yourself: "is it an exceptional case that the object is not found"? If it is expected to happen in the normal course of your program, you probably should not raise an exception (since it is not exceptional behavior).

Short version: use exceptions to handle exceptional behavior, not to handle normal flow of control in your program.

-Alan.

Answer 4

Prefer returning null --

If the caller uses it without checking, the exception happens right there anyway.

If the caller doesn't really use it, don't tax him a try/catch block

Answer 5

Don't think anyone mentioned the overhead in exception handling - takes additional resources to load up and process the exception so unless its a true app killing or process stopping event (going forward would cause more harm than good) I would opt for passing back a value the calling environment could interpret as it sees fit.

Answer 6

If you are using a library or another class which throws an exception, you should rethrow it. Here is an example. Example2.java is like library and Example.java uses it's object. Main.java is an example to handle this Exception. You should show a meaningful message and (if needed) stack trace to the user in the calling side.

Main.java

public class Main {
public static void main(String[] args) {
    Example example = new Example();

    try {
        Example2 obj = example.doExample();

        if(obj == null){
            System.out.println("Hey object is null!");
        }
    } catch (Exception e) {
        System.out.println("Congratulations, you caught the exception!");
        System.out.println("Here is stack trace:");
        e.printStackTrace();
    }
}
}

Example.java

/**
 * Example.java
 * @author Seval
 * @date 10/22/2014
 */
public class Example {
    /**
     * Returns Example2 object
     * If there is no Example2 object, throws exception
     * 
     * @return obj Example2
     * @throws Exception
     */
    public Example2 doExample() throws Exception {
        try {
            // Get the object
            Example2 obj = new Example2();

            return obj;

        } catch (Exception e) {
            // Log the exception and rethrow
            // Log.logException(e);
            throw e;
        }

    }
}

Example2.java

 /**
 * Example2.java
 * @author Seval
 *
 */
public class Example2 {
    /**
     * Constructor of Example2
     * @throws Exception
     */
    public Example2() throws Exception{
        throw new Exception("Please set the \"obj\"");
    }

}