"Math Quiz program by using GUI" how to make another math quiz appear if a JButton "Next" is pressed?
I'm doing a Math Quiz program by using GUI. This is my code, my problem now is 
1. how to make another question appear if the JButton [Next] is pressed.
2. how to make the JButton [Next] is work if and only if the answer is correct? (means that they must answer correctly before move to next question)

Someone help me please, thank you~

public class MathQuiz extends JFrame{
	
	JButton jbtNum1, jbtNum2, jbtNum3, jbtNum4, jbtNum5, jbtNum6, jbtNum7, jbtNum8, jbtNum9, jbtNum10, jbtNum11, jbtNum12, jbtNum13, jbtNum14, jbtNum15, jbtNum16, jbtNum17, jbtNum18, jbtNum19, jbtNum20;
	JButton jbtConfirm;
	JButton jbtNext;
	JTextField jtfAnswer = new JTextField();
	int a = (int)((Math.random())*10);
	int b = (int)((Math.random())*10);
	
	public MathQuiz(){
		
		JPanel p1 = new JPanel();
		p1.setLayout(new GridLayout(4,4,1,1));

			p1.add(jbtNum1 = new JButton("10"));
			p1.add(jbtNum2 = new JButton("7"));
			p1.add(jbtNum3 = new JButton("2"));
			p1.add(jbtNum4 = new JButton("18"));
			p1.add(jbtNum5 = new JButton("6"));
			p1.add(jbtNum6 = new JButton("11"));
			p1.add(jbtNum7 = new JButton("14"));
			p1.add(jbtNum8 = new JButton("1"));
			p1.add(jbtNum9 = new JButton("9"));
			p1.add(jbtNum10 = new JButton("3"));
			p1.add(jbtNum11 = new JButton("16"));
			p1.add(jbtNum12 = new JButton("17"));
			p1.add(jbtNum13 = new JButton("8"));
			p1.add(jbtNum14 = new JButton("15"));
			p1.add(jbtNum15 = new JButton("13"));
			p1.add(jbtNum16 = new JButton("5"));
			p1.add(jbtNum17 = new JButton("20"));
			p1.add(jbtNum18 = new JButton("12"));
			p1.add(jbtNum19 = new JButton("19"));
			p1.add(jbtNum20 = new JButton("4"));
			
		JPanel p2 = new JPanel(new GridLayout(1,5));
		
		p2.add(new JLabel(" " + a));
		p2.add(new JLabel(" + "));
		p2.add(new JLabel(" " + b));
		p2.add(new JLabel(" = "));
		p2.add(jtfAnswer);
		jtfAnswer.setEditable(false);
		p2.add(jbtConfirm = new JButton("Confirm"));
		p2.add(jbtNext = new JButton("Next"));
		
		setLayout(new GridLayout(3,1,50,50));
		add(p1);
		add(p2);

		jbtNum1.addActionListener(new ListenToButton());
		jbtNum2.addActionListener(new ListenToButton());
		jbtNum3.addActionListener(new ListenToButton());
		jbtNum4.addActionListener(new ListenToButton());
		jbtNum5.addActionListener(new ListenToButton());
		jbtNum6.addActionListener(new ListenToButton());
		jbtNum7.addActionListener(new ListenToButton());
		jbtNum8.addActionListener(new ListenToButton());
		jbtNum9.addActionListener(new ListenToButton());
		jbtNum10.addActionListener(new ListenToButton());
		jbtNum11.addActionListener(new ListenToButton());
		jbtNum12.addActionListener(new ListenToButton());
		jbtNum13.addActionListener(new ListenToButton());
		jbtNum14.addActionListener(new ListenToButton());
		jbtNum15.addActionListener(new ListenToButton());
		jbtNum16.addActionListener(new ListenToButton());
		jbtNum17.addActionListener(new ListenToButton());
		jbtNum18.addActionListener(new ListenToButton());
		jbtNum19.addActionListener(new ListenToButton());
		jbtNum20.addActionListener(new ListenToButton());
		jbtConfirm.addActionListener(new ListenToConfirm());
	}
	
	class ListenToButton implements ActionListener{
		public void actionPerformed(ActionEvent e){
			if(e.getSource() == jbtNum1)
				jtfAnswer.setText(jbtNum1.getText());
			else if(e.getSource() == jbtNum2)
				jtfAnswer.setText(jbtNum2.getText());
			else if(e.getSource() == jbtNum3)
				jtfAnswer.setText(jbtNum3.getText());
			else if(e.getSource() == jbtNum4)
				jtfAnswer.setText(jbtNum4.getText());
			else if(e.getSource() == jbtNum5)
				jtfAnswer.setText(jbtNum5.getText());
			else if(e.getSource() == jbtNum6)
				jtfAnswer.setText(jbtNum6.getText());
			else if(e.getSource() == jbtNum7)
				jtfAnswer.setText(jbtNum7.getText());
			else if(e.getSource() == jbtNum8)
				jtfAnswer.setText(jbtNum8.getText());
			else if(e.getSource() == jbtNum9)
				jtfAnswer.setText(jbtNum9.getText());
			else if(e.getSource() == jbtNum10)
				jtfAnswer.setText(jbtNum10.getText());
			else if(e.getSource() == jbtNum11)
				jtfAnswer.setText(jbtNum11.getText());
			else if(e.getSource() == jbtNum12)
				jtfAnswer.setText(jbtNum12.getText());
			else if(e.getSource() == jbtNum13)
				jtfAnswer.setText(jbtNum13.getText());
			else if(e.getSource() == jbtNum14)
				jtfAnswer.setText(jbtNum14.getText());
			else if(e.getSource() == jbtNum15)
				jtfAnswer.setText(jbtNum15.getText());
			else if(e.getSource() == jbtNum16)
				jtfAnswer.setText(jbtNum16.getText());
			else if(e.getSource() == jbtNum17)
				jtfAnswer.setText(jbtNum17.getText());
			else if(e.getSource() == jbtNum18)
				jtfAnswer.setText(jbtNum18.getText());
			else if(e.getSource() == jbtNum19)
				jtfAnswer.setText(jbtNum19.getText());
			else if(e.getSource() == jbtNum20)
				jtfAnswer.setText(jbtNum20.getText());
		}
	}
	
	class ListenToConfirm implements ActionListener{
		public void actionPerformed(ActionEvent e){
			int answer = a + b;
			int guessAnswer = Integer.parseInt(jtfAnswer.getText());
			
			if(guessAnswer == answer)
				jtfAnswer.setText("Correct");
			else
				jtfAnswer.setText("Wrong! Try Again.");
		}
	}
	
	public static void main(String[] args){
		MathQuiz frame = new MathQuiz();
		frame.setTitle("Math Quiz");
		frame.setSize(700,500);
		frame.setLocationRelativeTo(null);
		frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
		frame.setVisible(true);
	}
}



"Math Quiz program by using GUI" how to make another math quiz appear if a JButton "Next" is pressed?
===

I'm doing a Math Quiz program by using GUI. This is my code, my problem now is 
1. how to make another question appear if the JButton [Next] is pressed.
2. how to make the JButton [Next] is work if and only if the answer is correct? (means that they must answer correctly before move to next question)

Someone help me please, thank you~

public class MathQuiz extends JFrame{
	
	JButton jbtNum1, jbtNum2, jbtNum3, jbtNum4, jbtNum5, jbtNum6, jbtNum7, jbtNum8, jbtNum9, jbtNum10, jbtNum11, jbtNum12, jbtNum13, jbtNum14, jbtNum15, jbtNum16, jbtNum17, jbtNum18, jbtNum19, jbtNum20;
	JButton jbtConfirm;
	JButton jbtNext;
	JTextField jtfAnswer = new JTextField();
	int a = (int)((Math.random())*10);
	int b = (int)((Math.random())*10);
	
	public MathQuiz(){
		
		JPanel p1 = new JPanel();
		p1.setLayout(new GridLayout(4,4,1,1));

			p1.add(jbtNum1 = new JButton("10"));
			p1.add(jbtNum2 = new JButton("7"));
			p1.add(jbtNum3 = new JButton("2"));
			p1.add(jbtNum4 = new JButton("18"));
			p1.add(jbtNum5 = new JButton("6"));
			p1.add(jbtNum6 = new JButton("11"));
			p1.add(jbtNum7 = new JButton("14"));
			p1.add(jbtNum8 = new JButton("1"));
			p1.add(jbtNum9 = new JButton("9"));
			p1.add(jbtNum10 = new JButton("3"));
			p1.add(jbtNum11 = new JButton("16"));
			p1.add(jbtNum12 = new JButton("17"));
			p1.add(jbtNum13 = new JButton("8"));
			p1.add(jbtNum14 = new JButton("15"));
			p1.add(jbtNum15 = new JButton("13"));
			p1.add(jbtNum16 = new JButton("5"));
			p1.add(jbtNum17 = new JButton("20"));
			p1.add(jbtNum18 = new JButton("12"));
			p1.add(jbtNum19 = new JButton("19"));
			p1.add(jbtNum20 = new JButton("4"));
			
		JPanel p2 = new JPanel(new GridLayout(1,5));
		
		p2.add(new JLabel(" " + a));
		p2.add(new JLabel(" + "));
		p2.add(new JLabel(" " + b));
		p2.add(new JLabel(" = "));
		p2.add(jtfAnswer);
		jtfAnswer.setEditable(false);
		p2.add(jbtConfirm = new JButton("Confirm"));
		p2.add(jbtNext = new JButton("Next"));
		
		setLayout(new GridLayout(3,1,50,50));
		add(p1);
		add(p2);

		jbtNum1.addActionListener(new ListenToButton());
		jbtNum2.addActionListener(new ListenToButton());
		jbtNum3.addActionListener(new ListenToButton());
		jbtNum4.addActionListener(new ListenToButton());
		jbtNum5.addActionListener(new ListenToButton());
		jbtNum6.addActionListener(new ListenToButton());
		jbtNum7.addActionListener(new ListenToButton());
		jbtNum8.addActionListener(new ListenToButton());
		jbtNum9.addActionListener(new ListenToButton());
		jbtNum10.addActionListener(new ListenToButton());
		jbtNum11.addActionListener(new ListenToButton());
		jbtNum12.addActionListener(new ListenToButton());
		jbtNum13.addActionListener(new ListenToButton());
		jbtNum14.addActionListener(new ListenToButton());
		jbtNum15.addActionListener(new ListenToButton());
		jbtNum16.addActionListener(new ListenToButton());
		jbtNum17.addActionListener(new ListenToButton());
		jbtNum18.addActionListener(new ListenToButton());
		jbtNum19.addActionListener(new ListenToButton());
		jbtNum20.addActionListener(new ListenToButton());
		jbtConfirm.addActionListener(new ListenToConfirm());
	}
	
	class ListenToButton implements ActionListener{
		public void actionPerformed(ActionEvent e){
			if(e.getSource() == jbtNum1)
				jtfAnswer.setText(jbtNum1.getText());
			else if(e.getSource() == jbtNum2)
				jtfAnswer.setText(jbtNum2.getText());
			else if(e.getSource() == jbtNum3)
				jtfAnswer.setText(jbtNum3.getText());
			else if(e.getSource() == jbtNum4)
				jtfAnswer.setText(jbtNum4.getText());
			else if(e.getSource() == jbtNum5)
				jtfAnswer.setText(jbtNum5.getText());
			else if(e.getSource() == jbtNum6)
				jtfAnswer.setText(jbtNum6.getText());
			else if(e.getSource() == jbtNum7)
				jtfAnswer.setText(jbtNum7.getText());
			else if(e.getSource() == jbtNum8)
				jtfAnswer.setText(jbtNum8.getText());
			else if(e.getSource() == jbtNum9)
				jtfAnswer.setText(jbtNum9.getText());
			else if(e.getSource() == jbtNum10)
				jtfAnswer.setText(jbtNum10.getText());
			else if(e.getSource() == jbtNum11)
				jtfAnswer.setText(jbtNum11.getText());
			else if(e.getSource() == jbtNum12)
				jtfAnswer.setText(jbtNum12.getText());
			else if(e.getSource() == jbtNum13)
				jtfAnswer.setText(jbtNum13.getText());
			else if(e.getSource() == jbtNum14)
				jtfAnswer.setText(jbtNum14.getText());
			else if(e.getSource() == jbtNum15)
				jtfAnswer.setText(jbtNum15.getText());
			else if(e.getSource() == jbtNum16)
				jtfAnswer.setText(jbtNum16.getText());
			else if(e.getSource() == jbtNum17)
				jtfAnswer.setText(jbtNum17.getText());
			else if(e.getSource() == jbtNum18)
				jtfAnswer.setText(jbtNum18.getText());
			else if(e.getSource() == jbtNum19)
				jtfAnswer.setText(jbtNum19.getText());
			else if(e.getSource() == jbtNum20)
				jtfAnswer.setText(jbtNum20.getText());
		}
	}
	
	class ListenToConfirm implements ActionListener{
		public void actionPerformed(ActionEvent e){
			int answer = a + b;
			int guessAnswer = Integer.parseInt(jtfAnswer.getText());
			
			if(guessAnswer == answer)
				jtfAnswer.setText("Correct");
			else
				jtfAnswer.setText("Wrong! Try Again.");
		}
	}
	
	public static void main(String[] args){
		MathQuiz frame = new MathQuiz();
		frame.setTitle("Math Quiz");
		frame.setSize(700,500);
		frame.setLocationRelativeTo(null);
		frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
		frame.setVisible(true);
	}
}


