Create a new version of paste:

import java.awt.*;
import java.awt.event.*;

import javax.swing.*;
public class Lab9_1 extends JFrame implements ActionListener {
	Student std[];
	SubjectNew sub[];
	String studentStr[], subjectStr[];
	Container container;
	JComboBox stdCombo, subCombo;
	JLabel stdLabel, subLabel, addsubLabel, codeLabel, nameLabel, creditLabel;
	JLabel addstdLabel, stdcodeLabel, stdnameLabel, stdsurnameLabel;
	JButton addstdBtn, addsubBtn, saveBtn, clearBtn, cancleBtn;
	JButton addnewsubBtn, editsubBtn, deletesubBtn, clearsubBtn;
	JButton addnewstdBtn, editstdBtn, deletestdBtn, clearstdBtn;
	JTextField stdText, codeText, nameText, creditText, statusText;
	JTextField stdcodeText, stdnameText, stdsurnameText, stdstatusText;
	JTextArea subTextArea, subTextArea2, stdTextArea;
	JScrollPane subScroll, subScroll2;
	Register reg;
	int count = 0, money_total = 0, credit_total = 0;
	final int submax = 12, stdmax = 5;
	static Lab9_1 a;
	
	public Lab9_1() {
		super("ลงทะเบียน");
		initStudent();
		initSubject();
		initGui();
		reg = new Register(new Student(), 5);
		statusText.setText("Number Object : " + SubjectNew.getCount());
		stdstatusText.setText("Number Object : " + Student.getCount());
		subTextArea2.setText(readString(sub));
		stdTextArea.setText(readString(std));
	}
	
	public Lab9_1(Lab9_1 a) {
		super("ลงทะเบียน");
		this.a = a;
		initStudent();
		initSubject();
		initGui();
		reg = new Register(new Student(), 5);
		statusText.setText("Number Object : " + SubjectNew.getCount());
		stdstatusText.setText("Number Object : " + Student.getCount());
		subTextArea2.setText(readString(sub));
		stdTextArea.setText(readString(std));
	}
	
	public void initStudent() {
		std = new Student[stdmax];
		studentStr = new String[stdmax];
		std[0] = new Student("6066260010", "Pankamol", "Kaewboon");
		std[1] = new Student("6066260024", "Wikanda", "Wongjae");
		std[2] = new Student("6066260035", "Benjawan", "Punnam");
		studentStr[0] = std[0].toString();
		studentStr[1] = std[1].toString();
		studentStr[2] = std[2].toString();
	}
	
	public void initSubject() {
		sub = new SubjectNew[submax];
		subjectStr = new String[submax];
		sub[0] = new SubjectNew("662305", "IT Laboratory II", 1);
		sub[1] = new SubjectNew("662309", "Data Structure", 3);
		sub[2] = new SubjectNew("662310", "Database System", 3);
		sub[3] = new SubjectNew("662317", "Data Communication", 3);
		sub[4] = new SubjectNew("662327", "Advanced Computer Programming", 3);
		subjectStr[0] = sub[0].toString();
		subjectStr[1] = sub[1].toString();
		subjectStr[2] = sub[2].toString();
		subjectStr[3] = sub[3].toString();
		subjectStr[4] = sub[4].toString();
	}
	
	public void initGui() {
		String line = "                                             ";
		line += line;
		container = getContentPane();
		container.setLayout(new FlowLayout());
		
		stdLabel = new JLabel("Select Student : ");
		container.add(stdLabel);
		
		stdCombo = new JComboBox();
		for(int i=0;i<stdmax;i++) {
			if(studentStr[i] != null)
				stdCombo.addItem(studentStr[i]);
		}
		stdCombo.setMaximumRowCount(stdmax);
		container.add(stdCombo);
		
		addstdBtn = new JButton("Add Student");
		addstdBtn.addActionListener(this);
		container.add(addstdBtn);
		stdText = new JTextField(40);
		stdText.setEditable(false);
		container.add(stdText);
		
		subLabel = new JLabel("Select Subject : ");
		container.add(subLabel);
		
		subCombo = new JComboBox();
		for(int i=0;i<submax;i++) {
			if(subjectStr[i] != null)
				subCombo.addItem(subjectStr[i]);
		}
		subCombo.setMaximumRowCount(submax);
		container.add(subCombo);
		
		addsubBtn = new JButton("Add Subject");
		addsubBtn.setEnabled(false);
		addsubBtn.addActionListener(this);
		container.add(addsubBtn);
		
		subTextArea = new JTextArea(5, 40);
		subTextArea.setEditable(false);
		subScroll = new JScrollPane(subTextArea);
		container.add(subScroll);
		container.add(new JLabel("                             "));
		
		saveBtn = new JButton(" Save ");
		saveBtn.setEnabled(false);
		saveBtn.addActionListener(this);
		container.add(saveBtn);
		container.add(new JLabel("     "));
		
		cancleBtn = new JButton(" Cancle ");
		cancleBtn.setEnabled(false);
		cancleBtn.addActionListener(this);
		container.add(cancleBtn);
		container.add(new JLabel("                                     "));
		
		// ---- Add new subject
		addsubLabel = new JLabel("                 Add new subject");
		container.add(addsubLabel);
		
		container.add(new JLabel(line));
		codeLabel = new JLabel(" Subject Code : ");
		container.add(codeLabel);
		codeText = new JTextField(10);
		container.add(codeText);
		container.add(new JLabel("                                                   "));
		container.add(new JLabel("                       "));
		
		nameLabel = new JLabel(" Subject Name : ");
		container.add(nameLabel);
		nameText = new JTextField(20);
		container.add(nameText);
		container.add(new JLabel("                                 "));
		
		creditLabel = new JLabel("Subject Credit : ");
		container.add(creditLabel);
		creditText = new JTextField(5);
		container.add(creditText);
		container.add(new JLabel("     "));
		
		addnewsubBtn = new JButton("Add");
		addnewsubBtn.addActionListener(this);
		container.add(addnewsubBtn);
		
		editsubBtn = new JButton("Edit");
		editsubBtn.addActionListener(this);
		container.add(editsubBtn);
		
		deletesubBtn = new JButton("Delete");
		deletesubBtn.addActionListener(this);
		container.add(deletesubBtn);
		
		clearsubBtn = new JButton("Clear");
		clearsubBtn.addActionListener(this);
		container.add(clearsubBtn);
		subTextArea2 = new JTextArea(8, 25);
		subTextArea2.setEditable(false);
		subScroll2 = new JScrollPane(subTextArea2);
		container.add(subScroll2);
		
		statusText = new JTextField(30);
		statusText.setEnabled(false);
		container.add(statusText);
		
		// --------- Add new student
		addstdLabel = new JLabel("                 Add new student");
		container.add(addstdLabel);
		
		container.add(new JLabel(line));
		stdcodeLabel = new JLabel(" Student Code : ");
		container.add(stdcodeLabel);
		stdcodeText = new JTextField(10);
		container.add(stdcodeText);
		container.add(new JLabel("                                                   "));
		container.add(new JLabel("                   "));
		
		stdnameLabel = new JLabel(" Student Name : ");
		container.add(stdnameLabel);
		stdnameText = new JTextField(10);
		container.add(stdnameText);
		container.add(new JLabel("                                                    "));
		container.add(new JLabel("                   "));
		
		stdsurnameLabel = new JLabel("Student Surname : ");
		container.add(stdsurnameLabel);
		stdsurnameText = new JTextField(13);
		container.add(stdsurnameText);
		container.add(new JLabel("                                                    "));
		
		addnewstdBtn = new JButton("Add");
		addnewstdBtn.addActionListener(this);
		container.add(addnewstdBtn);
		
		editstdBtn = new JButton("Edit");
		editstdBtn.addActionListener(this);
		container.add(editstdBtn);
		
		deletestdBtn = new JButton("Delete");
		deletestdBtn.addActionListener(this);
		container.add(deletestdBtn);
		
		clearstdBtn = new JButton("Clear");
		clearstdBtn.addActionListener(this);
		container.add(clearstdBtn);
		stdTextArea = new JTextArea(8, 25);
		stdTextArea.setEditable(false);
		subScroll2 = new JScrollPane(stdTextArea);
		container.add(subScroll2);
		
		stdstatusText = new JTextField(30);
		stdstatusText.setEnabled(false);
		container.add(stdstatusText);
	}
	
	public void actionPerformed(ActionEvent event) {
		if(event.getSource() == addstdBtn) {
			int n = stdCombo.getSelectedIndex();
			int item = n;
			
			while(std[n] == null || std[n].toString().equals(stdCombo.getItemAt(item)) == false) {
				n++;
			}
			
			stdText.setText(std[n].toString());
			reg.setStudent(std[n]);
			addstdBtn.setEnabled(false);
			addsubBtn.setEnabled(true);
			saveBtn.setEnabled(true);
			cancleBtn.setEnabled(true);
		}
		else if(event.getSource() == addsubBtn) {
			int n = subCombo.getSelectedIndex();
			int item = n, credit;
			
			while(sub[n] == null || sub[n].toString().equals(subCombo.getItemAt(item)) == false) {
				n++;
			}

			if(count == 0) {
				credit = sub[n].getSubjectCredit();
				if(credit_total + credit > 10) {
					JOptionPane.showMessageDialog(this,  "ลงทะเบียนสูงสุดได้ไม่เกิน 10 หน่วยกิต",
							"Message", JOptionPane.INFORMATION_MESSAGE);
					return;
				}
				reg.setSubject(sub[n], count);
				subTextArea.append("[" + (++count) + "] " + sub[n].toString() + " จำนวน " + credit + " หน่วยกิต");
				subTextArea.append(" เป็นเงิน " + (credit * 500) + " บาท\n");
				credit_total += credit;
				money_total += credit * 500;
				saveBtn.setEnabled(true);
			}
			else {
				boolean chk = true;
				for(int j=0;j<count;j++) {
					if(sub[n].toString().equals(reg.getSubject(j))) {
						chk = false;
						break;
					}
				}
				if(chk) {
					credit = sub[n].getSubjectCredit();
					if(credit_total + credit > 10) {
						JOptionPane.showMessageDialog(this,  "ลงทะเบียนสูงสุดได้ไม่เกิน 10 หน่วยกิต",
								"Message", JOptionPane.INFORMATION_MESSAGE);
						return;
					}
					reg.setSubject(sub[n], count);
					subTextArea.append("[" + (++count) + "] " + sub[n].toString() + " จำนวน " + credit + " หน่วยกิต");
					subTextArea.append(" เป็นเงิน " + (credit * 500) + " บาท\n");
					credit_total += credit;
					money_total += credit * 500;
				}
			}
			if(count == 5) addsubBtn.setEnabled(false);
		}
		else if(event.getSource() == saveBtn) {
			String output = "";
			int credit = 0;
			output = "นักศึกษา : " + reg.getStudent();
			output += "\nวิชาที่ลงทะเบียน\n";
			for(int n = 0; n < count; n++) {
				credit = reg.getSubjectCredit(n);
				output += "[" + (n+1) + "] " + reg.getSubject(n) + " จำนวน " + credit + " หน่วยกิต";
				output += " เป็นเงิน " + (credit * 500) + " บาท\n";
			}
			output += "รวม "+ credit_total + " หน่วยกิต เป็นเงิน " + money_total + " บาท";
			JOptionPane.showMessageDialog(this,  output, "Registration Data", JOptionPane.INFORMATION_MESSAGE);
			resetBtn();
		}
		else if(event.getSource() == cancleBtn) {
			stdText.setText("");
			subTextArea.setText("");
			count = 0;
			resetBtn();
		}
		// ------- Subject button
		else if(event.getSource() == addnewsubBtn) {
			if(SubjectNew.getCount() == sub.length) {
				JOptionPane.showMessageDialog(this,  "Array full , can not add",
						"Message", JOptionPane.INFORMATION_MESSAGE);
				return;
			}
			int pos = CheckArrayEmpty();
			int n = Integer.parseInt(creditText.getText());
			sub[pos] = new SubjectNew(codeText.getText(), nameText.getText(), n);
			subTextArea2.setText(readString(sub));
			JOptionPane.showMessageDialog(this,  "Add Subject already", "Message", JOptionPane.INFORMATION_MESSAGE);
			clearTextField();
			updateGui();
		}
		else if(event.getSource() == editsubBtn) {
			String s = codeText.getText();
			int n = searchSubject(sub, s);
			if(n >= 5 ) {
				sub[n].setSubjectName(nameText.getText());
				sub[n].setSubjectCredit(Integer.parseInt(creditText.getText()));
				subTextArea2.setText(readString(sub));
				JOptionPane.showMessageDialog(this, "Edit Subject already", "Message", JOptionPane.INFORMATION_MESSAGE);
				clearTextField();
				updateGui();
			}
			else if(n >= 0) {
				JOptionPane.showMessageDialog(this, "Can not edit main subject", "Error Message", JOptionPane.ERROR_MESSAGE);
			}
			else {
				JOptionPane.showMessageDialog(this, "Can not found subject code", "Error Message", JOptionPane.ERROR_MESSAGE);
			}
		}
		else if(event.getSource() == deletesubBtn) {
			String s = codeText.getText();
			int n = searchSubject(sub, s);
			if(n >= 5) {
				nameText.setText(sub[n].getSubjectName());
				creditText.setText(sub[n].getSubjectCredit() + "");
				int ans = JOptionPane.showConfirmDialog(this, "Delete subject", "Confirm", JOptionPane.YES_NO_OPTION);
				if(ans == 0) {
					sub[n] = null;
					subjectStr[n] = null;
					System.gc();
					subTextArea2.setText(readString(sub));
					updateGui();
				}
				clearTextField();
			}
			else if(n >= 0) {
				JOptionPane.showMessageDialog(this, "Can not delete main subject", "Error Message", JOptionPane.ERROR_MESSAGE);
			}
			else {
				JOptionPane.showMessageDialog(this,  "Can not found subject code", "Error Messgae", JOptionPane.ERROR_MESSAGE);
			}
		}
		else if(event.getSource() == clearsubBtn) {
			clearTextField();
		}
		// ------- Student button
		else if(event.getSource() == addnewstdBtn) {
			if(Student.getCount() == std.length) {
				JOptionPane.showMessageDialog(this,  "Array full , can not add",
						"Message", JOptionPane.INFORMATION_MESSAGE);
				return;
			}
			int pos = CheckArrayEmpty2();
			std[pos] = new Student(stdcodeText.getText(), stdnameText.getText(), stdsurnameText.getText());
			stdTextArea.setText(readString(std));
			JOptionPane.showMessageDialog(this,  "Add Student already", "Message", JOptionPane.INFORMATION_MESSAGE);
			clearTextField2();
			updateGui2();
		}
		else if(event.getSource() == editstdBtn) {
			String s = stdcodeText.getText();
			int n = searchStudent(std, s);
			if(n >= 3 ) {
				std[n].setStudentName(stdnameText.getText());
				std[n].setStudentSurName(stdsurnameText.getText());
				stdTextArea.setText(readString(std));
				JOptionPane.showMessageDialog(this, "Edit Student already", "Message", JOptionPane.INFORMATION_MESSAGE);
				clearTextField2();
				updateGui2();
			}
			else if(n >= 0) {
				JOptionPane.showMessageDialog(this, "Can not edit main student", "Error Message", JOptionPane.ERROR_MESSAGE);
			}
			else {
				JOptionPane.showMessageDialog(this, "Can not found student code", "Error Message", JOptionPane.ERROR_MESSAGE);
			}
		}
		else if(event.getSource() == deletestdBtn) {
			String s = stdcodeText.getText();
			int n = searchStudent(std, s);
			if(n >= 3) {
				stdnameText.setText(std[n].getStudentName());
				stdsurnameText.setText(std[n].getStudentSurName());
				int ans = JOptionPane.showConfirmDialog(this, "Delete student", "Confirm", JOptionPane.YES_NO_OPTION);
				if(ans == 0) {
					std[n] = null;
					studentStr[n] = null;
					System.gc();
					stdTextArea.setText(readString(std));
					updateGui2();
				}
				clearTextField2();
			}
			else if(n >= 0) {
				JOptionPane.showMessageDialog(this, "Can not delete main student", "Error Message", JOptionPane.ERROR_MESSAGE);
			}
			else {
				JOptionPane.showMessageDialog(this,  "Can not found student code", "Error Messgae", JOptionPane.ERROR_MESSAGE);
			}
		}
		else if(event.getSource() == clearstdBtn) {
			clearTextField2();
		}
		statusText.setText("Number Object : " + SubjectNew.getCount());
		stdstatusText.setText("Number Object : " + Student.getCount());
	}
	
	public void resetBtn() {
		addstdBtn.setEnabled(true);
		addsubBtn.setEnabled(false);
		saveBtn.setEnabled(false);
		stdText.setText("");
		subTextArea.setText("");
		count = 0;
		money_total = 0;
		credit_total = 0;
	}
	
	public int CheckArrayEmpty() {
		for(int n = 0; n < sub.length; n++)
			if(sub[n] == null) return(n);
		return(-1);
	}
	
	public int CheckArrayEmpty2() {
		for(int n = 0; n < std.length; n++)
			if(std[n] == null) return(n);
		return(-1);
	}
	
	public void clearTextField() {
		codeText.setText("");
		nameText.setText("");
		creditText.setText("");
	}
	
	public void clearTextField2() {
		stdcodeText.setText("");
		stdnameText.setText("");
		stdsurnameText.setText("");
	}
	
	public void updateGui() {
		for(int i=0;i<sub.length;i++) {
			if(sub[i] != null)
				subjectStr[i] = sub[i].toString();
		}
		subCombo.removeAllItems();
		for(int i=0;i<submax;i++) {
			if(subjectStr[i] != null)
				subCombo.addItem(subjectStr[i]);
		}
	}
	
	public void updateGui2() {
		for(int i=0;i<std.length;i++) {
			if(std[i] != null)
				studentStr[i] = std[i].toString();
		}
		stdCombo.removeAllItems();
		for(int i=0;i<stdmax;i++) {
			if(studentStr[i] != null)
				stdCombo.addItem(studentStr[i]);
		}
	}
	
	public int searchSubject(SubjectNew sub[], String s){
		for(int n = 0; n < sub.length; n++) {
			if(sub[n] != null)
				if(s.equals(sub[n].getSubjectCode()))
					return(n);
		}
		return(-1);
	}
	
	public int searchStudent(Student std[], String s){
		for(int n = 0; n < std.length; n++) {
			if(std[n] != null)
				if(s.equals(std[n].getStudentCode()))
					return(n);
		}
		return(-1);
	}
	
	public String readString(SubjectNew sub[]) {
		String str = "";
		for(int n = 0; n < sub.length; n++) {
			if(sub[n] != null)
				str += sub[n].toString() + "\n";
		}
		return(str);
	}
	
	public String readString(Student std[]) {
		String str = "";
		for(int n = 0; n < std.length; n++) {
			if(std[n] != null)
				str += std[n].toString() + "\n";
		}
		return(str);
	}
	
	public static void main(String[] args) {
		Lab9_1 lab9_1 = new Lab9_1();
		lab9_1.setSize(500, 880);
		lab9_1.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
		lab9_1.setVisible(true);
	}
}