在Java中检查空值

Question

I'm trying to modify an Android app that is pulling some JSON from a server..

JSONObject mResult = new JSONObject((String) result);

Then using that to construct an object from my Sponsor class..

Gson mGson = new Gson();
mSponsor = mGson.fromJson(mResult.getJSONObject("data").getJSONObject("sponsor").toString(), Sponsor.class);

Sponsor class is just a shell with setters and getters, no logic done. Something like this:

public class Sponsor {

    @SerializedName("address1")
    private String Address1;
    @SerializedName("address2")
    private String Address2;

    public Sponsor(String address1, String address2) {
        Address1 = address1;
        Address2 = address2;
    }

    public Sponsor() {
        Address1 = "";
        Address2 = "";
    }

    public String getAddress1() {
        return Address1;
    }

    public void setAddress1(String address1) {
        Address1 = address1;
    }

    public String getAddress2() {
        return Address2;
    }

    public void setAddress2(String address2) {
        Address2 = address2;
    }
}

The app puts the address in a TextView like so:

txtAddress = (TextView) view.findViewById(R.id.txt_sponsor_address);
txtAddress.setText(mSponsor.getAddress1() + "\n" + mSponsor.getAddress2());

This all works, except when the server returns null for address2 , in which case the literal text "null" is printed in the TextView where address2 should be.

My question is how can i get rid of the "null"?

I've tried a few different things, started with a simple ternary statement and got more and more verbose and nothing has worked so for.

Here is the latest and most ridiculous-looking thing I've tried so far:

String addr2 = ((String) mSponsor.getAddress2()).trim();
String a2;
if((addr2 == "null") || (addr2 == "")) a2 = (String) "";
else a2 = (String) addr2;

txtAddress.setText(mSponsor.getAddress1() + "\n" + a2);

This causes the app to crash when I open that Activity.

I'm a noob at Java so please provide references if you can.

Answer 1

You could create another getter in your Sponsor class, where you'd put your logic to get a formatted address :

public String getFormattedAddress() {
    if (!TextUtils.isEmpty(Address1) && !TextUtils.isEmpty(Address2)
        && !Address1.equalsIgnoreCase("null") && !Address2.equalsIgnoreCase("null")) {
      return (Address1 + "\n" + Address2);
    }
    if (!TextUtils.isEmpty(Address1) && !Address1.equalsIgnoreCase("null")) {
      return (Address1);
    }
    if (!TextUtils.isEmpty(Address2) && !Address2.equalsIgnoreCase("null")) {
      return (Address2);
    }
    return ("");
}

And then simply setText with :

txtAddress.setText(mSponsor.getFormattedAddress());

Answer 2

"getAddress2()" isn't returning the literal string "null". It's returning a null reference and the StringBuilder is converting it to a "null" String when you print it in the concatenation. That's why it crashes when you try to trim the word.

A simple way to fix it is to put the ternary operator in the getter itself like so:

public String getAddress2() {
  return (Address2 == null) ? "" : Address2;
}

Now you'll never return a null reference and you can safely use it without any checks.

Answer 3

You should not use :

if((addr2 == "null")

For string comparaison use:

if (addr2.equalsIgnoreCase("null"))

Answer 4

String addr2 = mSponsor.getAddress2();
if(!TextUtils.isEmpty(addr2) || !addr2.equalsIgnoreCase("null")
     txtAddress.setText(mSponsor.getAddress1() + "\n" + addr2);
else
     txtAddress.setText(mSponsor.getAddress1());

Answer 5

How about this?

// if null, addr2="", if not null, addr = getAddress2()'s result 
String addr2 = mSponsor.getAddress2() == null ? "" : ((String) mSponsor.getAddress2()).trim();

txtAddress.setText(mSponsor.getAddress1() + "\n" + addr2);

Answer 6

Try this for your getter code:

 public String getAddress2() {
    if (Address2.equals("null")) {
        Address2="";
    }
    return Address2;
 }

Of course, you can do the same with your other getter for Address1 . Also, if you want to check for an empty string, use Address2.length() == 0 as opposed to Address2 == "" .