lib

int person_id=Integer.parseInt(person_id.getText());
/*
This person_id is taken from user from other class and called Person_detail class constructor which contains user interface code of this(Person_detail) class and set it visible(true) passed person id as:
*/
Person_detail ob=new Person_detail();
ob.setVisible(true);
ob.person_id=person_id;
ob.run();

/*
I am using class Person_detail implements Runnable.
Code is like this:
*/
int person_id;
ExecutorService exec ;
CompletableFuture<Void> t2;
public void run()
{
Person_detail r = this;
exec = Executors.newFixedThreadPool(3);
CompletableFuture<Void> t1=CompletableFuture.runAsync(() -> r.pageload(),exec );
t2=CompletableFuture.runAsync(() -> r.load_image(),exec );//line no. 612
}
synchronized void load_image()
{
try{
Class.forName("com.mysql.jdbc.Driver");
Connection con1=DriverManager.getConnection("jdbc:mysql://localhost:3306/"+dbsourcename,dbusername,dbpassword);
Statement stmt1 = con1.createStatement();
String sql1;
sql1 = "SELECT photo FROM readers where person_id="+Integer.toString(person_id);
ResultSet rs1 = stmt.executeQuery(sql1);//line no. 671
rs1.next();
if(rs1.getBlob("photo")!=null)
{ InputStream in = rs1.getBinaryStream("photo");
OutputStream f = new FileOutputStream(new File("photo.jpg"));
int c = 0;
while ((c = in.read()) > -1)
{
f.write(c);
}
f.close();
in.close();
BufferedImage img = null;
img = ImageIO.read(new File("photo.jpg"));
Image dimg;
dimg = img.getScaledInstance(jLabel9.getWidth(), jLabel9.getHeight(),Image.SCALE_SMOOTH);
ImageIcon pho=new ImageIcon(dimg);
jLabel9.setIcon(pho);
new File("photo.jpg").deleteOnExit();
} rs1.close();
stmt1.close();
con1.close();
}catch(Exception e)
{
e.printStackTrace();
JOptionPane.showMessageDialog(this,"Error : "+e,"Image display error",JOptionPane.ERROR_MESSAGE);
}
}
/*
Why sometimes I get Null pointer exception? (But sometimes not).
java.lang.NullPointerException
at librarymanagement.Person_detail.load_image(Person_detail.java:671)
at librarymanagement.Person_detail.lambda$run$1(Person_detail.java:612)
at java.util.concurrent.CompletableFuture$AsyncRun.run(CompletableFuture.java:1626)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
at java.lang.Thread.run(Thread.java:745)
*/