string concatenation in android studio java - string-concatenation

Question

I am trying to display invalid user credentials in textview by concatenating the invalid fields.So that i get a textview like invalid name,username,contact...at a time.
I want the invalid fields to display at a time.
I have declared a string and tried to concatenate but the result is textview displays all the fields even if its valid one.
boolean flag = true;
String s1,s2,s3,s4,s5;
boolean checkDataEntered() {
if (isEmpty(Name)) {
Name.setBackgroundResource(R.drawable.error);
s1="Full name";
flag = false;
}
if (isEmpty(Username)) {
Username.setBackgroundResource(R.drawable.error);
s2="Username";
flag = false;
}
if (isEmail(EmailId)) {
EmailId.setBackgroundResource(R.drawable.error);
s3="Email";
flag = false;
}
if (flag) {
return true;
} else {
textView7.setText("Please fill"+s1+ s2+ s3) ;
return false;
}
}

Answer 1

This is because you are concatenating all the fields in your else statement.
textView7.setText("Please fill"+s1+ s2+ s3);
But your requirement is to concatenate it only if it is empty. So you should try like,
boolean flag = true;
String error = "";
boolean checkDataEntered() {
if (isEmpty(Name)) {
Name.setBackgroundResource(R.drawable.error);
error += "Full name";
flag = false;
}
if (isEmpty(Username)) {
Username.setBackgroundResource(R.drawable.error);
error += ",Username";
flag = false;
}
if (isEmail(EmailId)) {
EmailId.setBackgroundResource(R.drawable.error);
error += ",Email";
flag = false;
}
if (flag) {
return true;
} else {
textView7.setText("Please fill "+error) ;
return false;
}
}