How to avoid the Null Pointer Exception from crashing my app? [duplicate] - java

This question already has answers here:
What is a NullPointerException, and how do I fix it?
(12 answers)
Closed 3 years ago.
ret_idx might be null for a new user since its entry in database is not made. So whenever the app detects ret_idx is null, it shows the java.lang.NullPointerException. How do I avoid this exception from crashing my app, considering ret_idx might go null in several cases.
String ret_idx=dataSnapshot.child("name").getValue().toString();


Check whether your input data is null or not and if not then assign it to ret_idx.
if(dataSnapshot.child("name").getValue() != null){
String ret_idx=dataSnapshot.child("name").getValue().toString();
}

Related

Check date for null [duplicate]

This question already has answers here:
Best way to check for null values in Java?
(19 answers)
Closed 3 years ago.
I want to check if date from database is empty like this:
private boolean hasAccountExpired(LocalDateTime password_changed_at) {
return password_changed_at.isEqual(null);
}
But I get NPE. What is the proper way to check if date field from database is empty?

password_changed_at == null will tell you if it's null.
However, this doesn't necessarily tell you if it's empty in the database - that depends on your implementation.

Java null pointer exception, when using JButton [duplicate]

This question already has answers here:
What is a NullPointerException, and how do I fix it?
(12 answers)
Closed 5 years ago.
code 1:
String s = Character.toString(button[0]);
bt[0].setText(s);//bt[]: JButton array;, button[] = char array
code 2:
String s = Character.toString(button[0]);
bt[0] = new JButton(s);
Suppose, I already initialize bt's by new JButton[num];
code 1 leads to null pointer exception, but code 2 run well.
I think bt's already has a pointer value of null. then, i can modify them without restriction. but it isn't.
I think code 2 initialize 2 times. but, it hasn't to be.

The problem is you initialized bt with new JButton[num];. But its content is still null, so bt[0] is null... So you try to run the method setText on a null reference.

i am getting java.lang.NullPointerException but i got value from textbox [duplicate]

This question already has answers here:
What is a NullPointerException, and how do I fix it?
(12 answers)
Closed 6 years ago.
What is the problem in my code?
orderIsbnDetails.setIsbn(request.getParameter("isbn"+ i).trim());
This line throws NullpointerException

request.getParameter("isbn"+ i)is null.
null.trim() causes NullPointerException.

Null pointer exception with linked hashmap [duplicate]

This question already has answers here:
What is a NullPointerException, and how do I fix it?
(12 answers)
Closed 8 years ago.
Crashlytics is showing a few crashes on the following line:
if(appObj.getStationsList().get(tag)!=null){
getStationsList() returns a LinkedHashMap<String, StationInfo>. How can I avoid getting this error? It's ironic that my very check to avoid this error actually resulted in it.

You will have to check:
if(appObj.getStationsList()==null)

replace
if(appObj.getStationsList().get(tag)!=null){
with
if(appObj.getStationsList() !=null && appObj.getStationsList().get(tag)!=null){
}

Why java prints null string as "null" instead of throwing a NullPointerException? [duplicate]

This question already has answers here:
Closed 11 years ago.
Possible Duplicate:
Why does null reference print as “null”
This is specified in java API. I wonder if this is for compatibility with previous versions of java, or has some other important reasons.

When converting to a String, having null in the message is often more useful than throwing a NullPointerException as you can at least see the rest of the message. The difference is likely to be a pragmatic decision.

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