Hi, can someone help me? I have two Jframes: Frame and MainFrame.
My problem is they both show at the same time.
If the login is correct MainFrame opens and Frame closes.

import javax.swing.*;

public class Main extends JFrame{
	public static void main(String args[]) {

//Frame Window /Login Window
	Frame fram = new Frame();
	fram.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
	fram.setSize(200,150);
	fram.setVisible(true);
	fram.setResizable(false);

//MainFrame Window
	MainFrame seal = new MainFrame();
	seal.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
	seal.setSize(200,150);
	seal.setVisible(true);
	seal.setResizable(true);

}}
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;

public class Frame extends JFrame{

private JButton login;
private JTextField user;
private JPasswordField pass;

	public Frame(){
	super("Login"); // title
	setLayout(new FlowLayout());

	user = new JTextField(10);
	add(user);
	pass = new JPasswordField(10);
	add(pass);
	login = new JButton("Login");
	add(login);
	maria louise = new maria();
	login.addActionListener(louise);
}

public class maria implements ActionListener{
	public void actionPerformed(ActionEvent e) {

	if(user.getText().trim().length()== 0 || pass.getText().length()==0)
	JOptionPane.showMessageDialog(null, "Please fill out both of the textbox");

	else if(user.getText().equals("12345") && pass.getText().equals("12345"))
	JOptionPane.showMessageDialog(null, " WELCOME");	

	else
	JOptionPane.showMessageDialog(null,"Wrong Username or Password");

}}

}
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;

public class MainFrame extends JFrame{

	private JLabel item1;
	private JTextField item2, item3;

		public MainFrame(){
		super("Main Window");
		setLayout(new FlowLayout());

		item1 = new JLabel("Welcome");
		item1.setToolTipText("Hello");
		add(item1);
	
		item2 = new JTextField(15);
		add(item2);
	
		item3 = new JTextField(15);
		add(item3);

	}}

Class Main lines 10, 17 you make them both visible. Don't make mainframe window visible until after logon.

you declare two frame in the main method.For this reason these two open at a time.
Delete this....

//MainFrame Window
	MainFrame seal = new MainFrame();
	seal.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
	seal.setSize(200,150);
	seal.setVisible(true);
	seal.setResizable(true);

I think now you can solve the problem.....

Class Main lines 10, 17 you make them both visible. Don't make mainframe window visible until after logon.

How do I do it?

sealxlion
JamesCherrill's reply and my reply is same.
Delete code for mainframe from the main method that I have said before.

Unrelated to your question, but a general advice: do not do this

public class Frame extends JFrame{

JFrame itself extends java.awt.Frame . You're just asking for confusion and possible bugs by naming your class Frame.

commented: Good post. +0
commented: very good point +9

@Ezzaral very good point +1

@sealxlion don't mixing Java AWT Frame with Swing JFrame, that really road to the hell,

for todays GUI is required --> all Components must starts with Char J

then Frame fram = new Frame(); should be JFrame fram = new JFrame();

and as @Ezzaral suggested correctly, this is twice definitions