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I'm having an issue with multiple NullPointerExceptions, I'm getting one for my if statements within iterators and I can't figure out why
one of the problem blocks:
public int removeAllBooks(String author, String title){
Iterator<Book> itr=library.iterator();
int i=0;
while(itr.hasNext()){
Book book=itr.next();
if(b.getAuthor().equals(author)&&(b.getTitle().equals(title))){
itr.remove();
i++;
}
if(i>0){
return i;
}
}
return 0;
}
The NPE error points to my if-statement line for some reason.
Thanks.
What is b? Where is it declared/initialized? Your itr.next() is assigned to the book variable, not b.
You code should probably be :
Book book=itr.next();
if(book.getAuthor().equals(author)&&(book.getTitle().equals(title))){
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I'm trying modification of an instance's fields through Java reflection.
Here is my original code.
for(Field f: customerClass.getDeclaredFields()) {
System.out.println(f);
}
System.out.println("\n");
System.out.println(customerClass.getDeclaredField("firstName"));
for(int i=0; i < columnNames.length; i++) {
System.out.println(columnNames[i]);
field = customerClass.getDeclaredField(columnNames[i]);
field.setAccessible(true);
And the results.
private java.lang.String Customer.firstName
private java.lang.String Customer.lastName
private java.lang.String Customer.firstName
"firstName"
java.lang.NoSuchFieldException: "firstName"
at java.lang.Class.getDeclaredField(Class.java:2070)
I am wondering why "customerClass.getDeclaredField("firstName")" works, but "customerClass.getDeclaredField(columnNames[i])" throws an Exception, since columnNames[0] == "firstName".
If you'll look at your output for columnNames[0], you'll see that it's not firstName, it's "firstName". Remove the quotes and it should work.
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recently my teacher showed us how to make a summ methode but i cant remember it.I think i got it a bit ritght.But it tells me error unexpected token a
void main(){
summ(6, 7);
}
int summ(a, b){
a = int
b = int
return a+b }
It should be like this
static int summ(int a, int b)
{
return a+b;
}
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I'm new and would like to find and correct my errors. I got 2 errors while writing a java program to print prime nos. between 1 to 20.
code:
error:
; instead of ,
for (i=1;i<20;i++)
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am writing a java program as below.
Void fun(int n){
for(int i=0;i<=n;i++){
fun(n-i);
}
System.out.println(“well done”);
}
I am getting error, missing return statement. I not used int or string method. It is void method na. why it asking return type, please help for this problem.
Void is a reference type.
void is a language primitive.
You don't need a return statement when your return type is void.
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Can you please help me make the following code work?
for(int a=0, b=0; a<101; b<102; a++; b++;) {
stuff
}
You got the initialization (first) part of the loop right.
The termination or condition (second) part of the loop should be evaluated to a boolean, so assuming you require an AND relation between the conditions on a and b, it becomes a<101 && b<102. You might want || (OR) instead, depending on your logic.
The increment (third) part of the loop should contain comma separated expressions (same as the initialization part which you already got right).
I also removed an extra ';' from the end.
for(int a=0, b=0; a<101 && b<102; a++, b++) { stuff }