Question

I had a lot of testcases running on the class MyClass, using it’s default constructor: MyClass().

Now the requirements of MyClass changed and the user can provide a HashMap to indicate some pairs . Now a MyClass needs to have at least one pair and throws exceptions if one of those is null.

I was hoping to create another default constructor to avoid having to rewrite all the test methods something like:

public MyClass() {

  HashMap<KeyClass, ValueClass> hashMap = HashMap<KeyClass, ValueClass>();
  hashMap.put(KeyClass.someValue, new ValueClass());
  this(hashMap);

}

Now this doesn’t work, because i have to call the other constructor first, so i thought of writing some method

private static HashMap<KeyClass, ValueClass> getDefaultHashmap();

and using it to call the other constructor like this:

public MyClass() {

  this(MyClass.getDefaultHashmap());

}

But this seemed to me as not really good style, so i was hoping you could tell me what the right way to do something like this is!

Answer 1

You could inline the HashMap creation:

public MyClass() {
    this(new HashMap<KeyClass, ValueClass>() {{
        put(KeyClass.someValue, new ValueClass());
    }});
}

But you’d have to ignore the serial-id warning to keep it “pretty”.