Nullpointer exception in my code..please help me.....

[danpotter]

Well..i know java basics..but new to code something new...so please help me...im getting error

Exception in Thread "main" java.lang.nullpointerException
at lms.<init> (lms.java27)
at lms.main (lms.java76)

actually my main aim is to make a sample library management system and the member can go to management system[frame 2] only if the given username and password are same...if not a show a message[i.e,.label] will be displayed on the frame "Login Failed Please check..."..ofcourse..i still didnt write any code for frame 2 ..,but still within frame 1 only im getting this null pointer error...

please help me..and also explain me why the error occured and how u removed that..pls...

code is:-

//Library Management System//

import java.awt.*;
import java.awt.event.*;
class lms extends Frame implements ActionListener{
	TextField name,pswd;
	Label lbl1,lbl2,lbl3,lbl4;
	Button b1;
	lms(){
	System.out.println("Welcome to the Online Library Management System");
	lbl1=new Label("Name : ",Label.LEFT);
	lbl2=new Label("Password : ",Label.LEFT);
	lbl3=new Label("Welcome To Library Management System",Label.CENTER);

		name=new TextField(20);
		pswd=new TextField(20);
		pswd.setEchoChar('*');
		b1=new Button("OK");
		name.setBackground(Color.pink);
		name.setForeground(Color.blue);
		Font f=new Font("Arial",Font.BOLD,15);
		Font z=new Font("Arial",Font.ITALIC+Font.BOLD,15);
		name.setFont(f);
		lbl1.setFont(f);
		lbl2.setFont(f);
		lbl3.setFont(z);
		lbl4.setFont(f);
		pswd.setFont(f);
		b1.setFont(f);
		
		lbl1.setBounds(50,200,80,20);
		lbl2.setBounds(50,250,80,20);
		lbl3.setBounds(150,80,350,100);
		lbl4.setBounds(150,80,350,100);
		name.setBounds(150,200,120,25);
		pswd.setBounds(250,350,100,35);
		setLayout(null);
		
	
		b1.setFont(f);
		
		b1.setBounds(200,300,50,30);
		
	
		b1.addActionListener(this);
		
		add(lbl3);
		add(lbl1);
		add(name);
		add(lbl2);
		add(pswd);
		add(b1);
		add(lbl4);
		setSize(1000,1000);
		setTitle("LIBRARY MANAGEMENT SYSTEM");
		setVisible(true);

		addWindowListener(new WindowAdapter(){
			public void windowClosing(WindowEvent e){
				System.exit(0);
			}
		});	
	
	}

	public void actionPerformed(ActionEvent ae){
                String s1=name.getText();
			String s2=pswd.getText();		
if(ae.getSource()==b1 && s1.equals(s2)){
			System.out.println("success");}
else{
lbl4=new Label("Login Failed Please check...",Label.LEFT);}
		
}
	public static void main(String args[]){
lms l1= new lms();
	}
}

[eRaaaa]

Exception in Thread "main" java.lang.nullpointerException
at lms.<init> (lms.java27)

Line 27 = lbl4.setFont(f);
you realize yourself the error now?

lbl1=new Label("Name : ",Label.LEFT);
lbl2=new Label("Password : ",Label.LEFT);
lbl3=new Label("Welcome To Library Management System",Label.CENTER);
...
there is some line missing :-)

[danpotter]

but i gave code in else block

else{
lbl4=new Label("Login Failed Please check...",Label.LEFT);}

}

[eRaaaa]

Yes but the line 34 is invoked previously - and at this time, its still null!

[Tolls]

As eRaaa says, until that else block executes then lbl4 is null.
Hence your NullPointerException.

[danpotter]

so what i exactly need to do now???what modification?? how can i display warning mssge in frame when else condition occur??

[eRaaaa]

I'll give you a good council : learn the basics before programming gui applications! scnr!

[Tolls]

Create a blank label at the same place as the others, then set the text when there's an error.

[danpotter]

ok..got u,.. :D

[danpotter]

@tolls problem solved thnx dude... :)