问题
What is the difference between getString() and optString() in JSON?
回答1:
As Diego mentions, it's a good idea to check the documentation (this link is now out of date - good thing we have the Wayback Machine!) before posting a question here, but now that you have:
The difference is that optString returns the empty string ("") if the key you specify doesn't exist. getString on the other hand throws a JSONException. Use getString if it's an error for the data to be missing, or optString if you're not sure if it will be there.
Edit: Full description from the documentation:
Get an optional string associated with a key. It returns an empty string if there is no such key. If the value is not a string and is not null, then it is converted to a string.
回答2:
If you want to avoid NullPointerException you better make use of optString()
If you are fetching the data from JSON at any time, you might have null data for a particular Key value, at that time instead of implementing Null conditions, better make use of this optimized method optString("<keyname>")
回答3:
public java.lang.String optString(int index) Get the optional string value associated with an index. It returns an empty string if there is no value at that index. If the value is not a string and is not null, then it is coverted to a string. Parameters: index - The index must be between 0 and length() - 1. Returns: A String value.
回答4:
1) getString (String name):- This method Returns the String value mapped by name if it exists, coercing it if necessary, or throws JSONException if no such mapping exists.
2)optString (String name):- This method Returns the String value mapped by name if it exists, coercing it if necessary, or the empty string ("") if no such mapping exists.
回答5:
optString() is used to overcome NullPointerException, which we get while using getString() when the required key doesn't exists in json it basically replaces with the default value.
example let the input Json be
{
"name":"abhi",
"country":"india"
}
now in java when you execute
String city = json.getString("city");
it will throw a NullPointerException.
by using optString(String key, String default) we can overcome the above problem.
String city= json.optString("city","default");
System.out.println(city);
Output: default
来源：https://stackoverflow.com/questions/13790726/the-difference-between-getstring-and-optstring-in-json