JDBC and new null pointer exceptions, java JDBC null pointer exceptions

Null pointer exceptions are generally some objects that are not instantiated.

If you just want to store data, like the underlying data type, the system will give it an initial value, and you won't have this error.

So it can only be a complex data type above string, and you can manually initialize it in the constructor, such as string s="";

If you modify your own database, it is allowed to be empty.

Breakpoint debugging, bearish pointer appears in **? Remember to use the eclipse power off debugging, soon. Hehe.

Even if it's empty, you don't have to judge it, I don't know what the difficulties encountered by the landlord can you be more detailed.

It should be that the data type is inconsistent, take a look at the exception information.

Break the point in the getperson method to excite the round sail to see if the jdbctemplate variable is empty. 99% likely to be empty, which means that your jdbctemplate is not injected correctly, confirm that your spring configuration file is personservicbean and is indeed injected into datasource.

When you call the getperson() method, jdbctemplate is not clear, it is not initialized!

In the getperson() method, the answer is to guess whether the jdbctemplate is null, and if it is null, it initializes the megabeam.

public listgetperson()if(

setdatasource(your datasource);

Is your setdatasource method executed? You should use the constructor to set the value. You can print a copy of your jdbctemplate that is not null, and it is recommended that you inherit the jdbctemplate class directly.

The main function contains the following:

for(i=0;i. "Laughing N-1; i++)

s[i].next=&s[i+1];

s[n].next=null;The crack here should be s[n-1].next = null;

All I think of are low-level errors.

Copy the address to the program to prevent minor mistakes.

Swap in the path

Check the program context.

First, the file may not really exist. Second, the file may be being opened in an exclusive way.

See if you instantiate the object when you use it, and if you don't, you can't call its method, otherwise a null pointer exception will be thrown.

Output path before this sentence and see what the result is.