This question already has answers here:
What is a NullPointerException, and how do I fix it?
(12 answers)
Closed 4 years ago.
Boolean valid = null;
if (valid == null) {
log.info("******");
}
I have the expression above, I wanted to check if Boolean value is null and if it is then execute statement inside if clause, but what happened is that it throws me a NullPointerException. What should I do to have my if clause evaluated with that given condition valid == null.
Thanks in advance
For sure, your log object contains null reference. You can't invoke any method with null reference. Try this:
Boolean valid = null;
if(valid == null) {
System.out.println("Hello");
}
Related
This question already has answers here:
What is a NullPointerException, and how do I fix it?
(12 answers)
Closed 4 years ago.
how to check my jtable if null pointer?
my code is always null pointer and then can't export to xls.
this my code
if (tbGudangSales.getValueAt(i, 5).toString().trim().length() == 0) {
status = "tidak ada penjualan";
} else{
status = tbGudangSales.getValueAt(i, 5).toString();
}
label = new Label(4, baris, status, bordertabel);
excelSheet.addCell(label);
this my error
this my value table
All you need to do is to check if the value is null. For example:
Object value = tbGudangSales.getValueAt(i, 5);
if (value != null)
{
if(value.toString().trim().isEmpty()) // instead checking the length "manually", you can use the isEmpty() method
{
status = "tidak ada penjualan";
}
else
{
status = value.toString();
}
}
This question already has answers here:
What is a NullPointerException, and how do I fix it?
(12 answers)
Closed 4 years ago.
when objec is null:
if(object != null && object.string.equals("")) {
System.out.println("no error");
}
it will result in NullPointerException, and why if it checks the first result is false, it still check the second instead of stop check and print "no error"?
sorry for my bad english -_-#
It's not object which is null but object.string.
Try: (object != null && "".equals(object.string))
This question already has answers here:
What is a NullPointerException, and how do I fix it?
(12 answers)
Closed 6 years ago.
this is my code to check if the value of column is not null
if(!res.getString(res.getColumnIndex("answerquestionid")).trim().equals("")){
but I get this:
java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String java.lang.String.trim()' on a null object reference
What is the proper way to check if value return by res is empty
Try this,
if(res != null){
if(res.getString(res.getColumnIndex("answerquestionid")) != null && !res.getString(res.getColumnIndex("answerquestionid")).trim().equals(""))
//your stuff
}
Try this:
if(res.getString(res.getColumnIndex("answerquestionid"))!=null){
You have two ways for it:
First is checking if res exists (best approach)
if(res.getIdentifier(myStringName) != 0){
//do stuff
}
Because if it returns 0 it means it doesn't exists.
Second way is checking if string is null
String myRes = res.getString(myStringName);
if(myRes != null && !myRes.trim().equals("")){
//do stuff
}
Your problem was that you were not checking if the String result was null
Hope this helps
You are checking the value of something which may be null, which will throw a Null object reference. to fix this you must check if the String is null.
if (res != null) {
String str = res.getString(res.getColumnIndex("answerquestionid"));
if(str != null) {
// Perform action
} else {
// String is null so recover (use placeholder, try again etc)
}
}
alternativley you can do it in one if statement but I find the above more readable.
if (res != null) {
if( res.getString(res.getColumnIndex("answerquestionid")) != null &&
res.getString(!res.getColumnIndex("answerquestionid")).trim().equals("")) {
//Safe to use String
}
}
This question already has answers here:
What is a NullPointerException, and how do I fix it?
(12 answers)
Closed 7 years ago.
in Line 7 i get nullpointerexception, how can i fix that ? any ideas?
private void updateHeights(BSTreeNode v) {
BSTreeNode u = v;
while (u != null) {
int bfc=updateNodeHeight(u);
u = u.parent;
if (bfc<=-2) {
if( getHeight(u.left.left) >= getHeight(u.left.right) ) { // Null Pointer Exception
u = rotateRight(u);
} else {
u=LR(u);
}
}
}
}
There are two possibel problems, and as many solutions. First is placing a null check in getHeight() which I assume has been done based on your programming style (the check in while conditional). That leaves a possible null pointer issue with u.left. As such:
Ensure u.left is not null, like this:
getHeight(u.left != null && ((u.left.left)>=getHeight(u.left.right))
This question already has answers here:
What is a NullPointerException, and how do I fix it?
(12 answers)
Closed 8 years ago.
I wrote this statement in the main method
the Exception will be in the (GuaranteeYears) so i put it in the try block.
First in the main I make a Store object and pass number 4 in parameter, in the Store class I will have a array called arrProduct that will have the length 4:
boolean flag1 = true;
while (flag1) {
try {
System.out.println("Ente GuaranteeYears");
int GuaranteeYears=read.nextInt();
StrongDevice s = new StrongDevice(code,type,price,Model,Capacity,GuaranteeYears); //the object
flag1 = false;
x.addProduct(s);
}
and this is my add method
public boolean addProduct(Product p) {
if(arrProduct.length==NumOfProduct)
return false;
arrProduct[NumOfProduct]=p;
NumOfProduct++;
return true;
}
My question is: when I make the object and add it to the array it gives me NullPointerException - why that happened?
As far as I understood, the line which cause NPE is
x.addProduct(s);
Most likely this is caused by array arrProduct which is not initialized and cause NPE when it is being accessed.
To fix that, please verify that arrProduct is always correctly initialized at Store object creation.