如何为多个if-else语句编写函数

Question

I am new to Java. I have lots of multiple if-else statements. For code optimization purpose I need to write one function for all if else logic.

if (obj.getJSONObject("page_1").has("city")) {
    sn.city = (String) obj.getJSONObject("page_1").get("city").toString();
} else {
    sn.city = null;
}

// param 2 - locality

if (obj.getJSONObject("page_1").has("locality")) {
    locality = (String) obj.getJSONObject("page_1").get("locality").toString();
} else {
    locality = null;
}

I have like 110 if -else statements. I don't have any idea how to optimize the code.

Answer 1

I might write a function something like:

static String getToStringOrNull(JSONObject parent, String key) {
  return parent.has(key) ? parent.get(key).toString() : null;
}

which you can then call like

sn.city = getToStringOrNull(obj.getJSONObject("page_1"), "city");
locality = getToStringOrNull(obj.getJSONObject("page_1"), "locality");

Answer 2

I think the best use would be this notation ( ternary operator ):

sn.city = (obj.getJSONObject("page_1").has("city")) ? 
                    (String) obj.getJSONObject("page_1").get("city").toString() : null;

The part before ? stands for the if-statement, the second part if the condition was fulfilled and the last part otherwise.

Answer 3

For all direct fields of your class, you may use reflection (and you could do the same work on the sn object if you want ) :

Class aClass = this.getClass();

Field[] fields = aClass.getFields();

for (Field field : fields) {


   String value = (obj.getJSONObject("page_1").has(field.getName())) ?
            (String) obj.getJSONObject("page_1").get(field.getName()).toString() : null;

   field.set(this, value);
}