import java.awt.BorderLayout;
import java.awt.Container;
import java.awt.FlowLayout;
import java.awt.GridLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JTextField;

public class CalculatorFrame extends JFrame {
	
	private String str1 = "";
	private String str2 = "";
	private StringBuffer str = new StringBuffer("");
	private char ch1;
	private char ch2;
	private boolean minusFlag;
	private boolean hasPoint;
	
	private JTextField jtf = new JTextField();
	
	private JPanel jpUp = new JPanel();
	private JPanel jpCenter = new JPanel();
	
	private JButton jb1 = new JButton("1");
	private JButton jb2 = new JButton("2");
	private JButton jb3 = new JButton("3");
	private JButton jb4 = new JButton("4");
	private JButton jb5 = new JButton("5");
	private JButton jb6 = new JButton("6");
	private JButton jb7 = new JButton("7");
	private JButton jb8 = new JButton("8");
	private JButton jb9 = new JButton("9");
	private JButton jb0 = new JButton("0");
	
	private JButton jbPoint = new JButton(".");
	private JButton jbCPL = new JButton("+/-");
	
	private JButton jbAdd = new JButton("+");
	private JButton jbMinus = new JButton("-");
	private JButton jbMulti = new JButton("*");
	private JButton jbDivide = new JButton("/");
	
	private JButton jbResult = new JButton("=");
	
	private JButton jbBackspace = new JButton("Backspace");
	private JButton jbC = new JButton("C");
	private JButton jbCE = new JButton("CE");
	
	public void go() {
		jpUp.setLayout(new BorderLayout());
		
		jpUp.add(jtf, BorderLayout.CENTER);
		
		JPanel jpUpDown = new JPanel();
		jpUpDown.setLayout(new FlowLayout(FlowLayout.RIGHT, 5, 5));
		jpUpDown.add(jbBackspace);
		jpUpDown.add(jbC);
		jpUpDown.add(jbCE);
		jpUpDown.add(jbResult);
		
		jpUp.add(jpUpDown, BorderLayout.SOUTH);
		
		
		JPanel jpCenterLeft = new JPanel();
		jpCenterLeft.setLayout(new GridLayout(4, 1, 5, 5));
		jpCenterLeft.add(jbAdd);
		jpCenterLeft.add(jbMinus);
		jpCenterLeft.add(jbMulti);
		jpCenterLeft.add(jbDivide);
		
		JPanel jpCenterCenter = new JPanel();
		jpCenterCenter.setLayout(new GridLayout(4, 3, 5 ,5));
		jpCenterCenter.add(jb7);
		jpCenterCenter.add(jb8);
		jpCenterCenter.add(jb9);
		jpCenterCenter.add(jb4);
		jpCenterCenter.add(jb5);
		jpCenterCenter.add(jb6);
		jpCenterCenter.add(jb1);
		jpCenterCenter.add(jb2);
		jpCenterCenter.add(jb3);
		jpCenterCenter.add(jb0);
		jpCenterCenter.add(jbCPL);
		jpCenterCenter.add(jbPoint);
	
		
		jpCenter.setLayout(new BorderLayout(5, 5));
		jpCenter.add(jpCenterCenter);
		jpCenter.add(jpCenterLeft, BorderLayout.WEST);
		
		Container container = getContentPane();
		container.add(jpUp, BorderLayout.NORTH);
		container.add(jpCenter);
	
		jtf.setHorizontalAlignment(JTextField.RIGHT);
	}

	public void addAllListeners() {
		jb1.addActionListener(new ActionListener() {
			public void actionPerformed(ActionEvent e) {
				str.append("1");
				jtf.setText(str.toString());
			}
		});
		jb2.addActionListener(new ActionListener() {
			public void actionPerformed(ActionEvent e) {
				str.append("2");
				jtf.setText(str.toString());
			}
		});
		jb3.addActionListener(new ActionListener() {
			public void actionPerformed(ActionEvent e) {
				str.append("3");
				jtf.setText(str.toString());
			}
		});
		jb4.addActionListener(new ActionListener() {
			public void actionPerformed(ActionEvent e) {
				str.append("4");
				jtf.setText(str.toString());
			}
		});
		jb5.addActionListener(new ActionListener() {
			public void actionPerformed(ActionEvent e) {
				str.append("5");
				jtf.setText(str.toString());
			}
		});
		jb6.addActionListener(new ActionListener() {
			public void actionPerformed(ActionEvent e) {
				str.append("6");
				jtf.setText(str.toString());
			}
		});
		jb7.addActionListener(new ActionListener() {
			public void actionPerformed(ActionEvent e) {
				str.append("7");
				jtf.setText(str.toString());
			}
		});
		jb8.addActionListener(new ActionListener() {
			public void actionPerformed(ActionEvent e) {
				str.append("8");
				jtf.setText(str.toString());
			}
		});
		jb9.addActionListener(new ActionListener() {
			public void actionPerformed(ActionEvent e) {
				str.append("9");
				jtf.setText(str.toString());
			}
		});
		jb0.addActionListener(new ActionListener() {
			public void actionPerformed(ActionEvent e) {
				str.append("0");
				jtf.setText(str.toString());
			}
		});
		jbAdd.addActionListener(new ActionListener() {
			public void actionPerformed(ActionEvent e) {
				opMethod('+');
			}
		});
		jbMinus.addActionListener(new ActionListener() {
			public void actionPerformed(ActionEvent e) {
				opMethod('-');
			}
		});
		jbMulti.addActionListener(new ActionListener() {
			public void actionPerformed(ActionEvent e) {
				opMethod('*');
			}
		});
		jbDivide.addActionListener(new ActionListener() {
			public void actionPerformed(ActionEvent e) {
				opMethod('/');
			}
		});
		
		jbResult.addActionListener(new ActionListener() {
			public void actionPerformed(ActionEvent e) {
				str2 = str.toString();
				int int1 = Integer.parseInt(str1);
				int int2 = Integer.parseInt(str2);
				int result = 0;
				switch(ch1) {
				case '+': result = int1 + int2;break;
				case '-': result = int1 - int2;break;
				case '*': result = int1 * int2;break;
				case '/': result = int1/int2;break;
				}
				jtf.setText("" + result);
				str.delete(0, str.length());
				str1 = "";
				str2 = "";
			}
		});
	
		jbBackspace.addActionListener(new ActionListener() {
			public void actionPerformed(ActionEvent e) {
				str.deleteCharAt(str.length() - 1);
				jtf.setText(str.toString());
			}
		});
	
		jbCE.addActionListener(new ActionListener() {
			public void actionPerformed(ActionEvent e) {
				str.delete(0, str.length());
				jtf.setText(str.toString());
			}
		});
		
		jbC.addActionListener(new ActionListener() {
			public void actionPerformed(ActionEvent e) {
				str.delete(0, str.length());
				str1 = "";
				str2 = "";
				jtf.setText(str.toString());
			}
		});
		
		jbCPL.addActionListener(new ActionListener() {
			public void actionPerformed(ActionEvent e) {
				if(!minusFlag) {
					str.insert(0, '-');
					jtf.setText(str.toString());
				}
				else {
					str.deleteCharAt(0);
					jtf.setText(str.toString());
				}
				minusFlag = true;
			}
		});
	
		jbPoint.addActionListener(new ActionListener() {
			public void actionPerformed(ActionEvent e) {
				str.append('.');
				hasPoint = true;
			}
		});
	}
	
	public void opMethod(char op) {
		if(!IsTwo()) {
			str1 = str.toString();
			ch1 = op;
			ch2 = op;
			str.delete(0, str.length());
			ch1 = ch2;
		}
		else {
			ch2 = op;
			str2 = str.toString();
			int int1 = Integer.parseInt(str1);
			int int2 = Integer.parseInt(str2);
			int result = 0;
			switch(ch1) {
			case '+': result = int1 + int2;break;
			case '-': result = int1 - int2;break;
			case '*': result = int1 * int2;break;
			case '/': result = int1/int2;break;
			}
			jtf.setText("" + result);
			str1 = String.valueOf(result);
			str2 = "";
			str.delete(0, str.length());
			ch1 = ch2;
		}
	}
	
	public boolean IsTwo() {
		if(!str1.equals("") | !str2.equals("")) 
			return true;
		return false;
	}


	public static void main(String[] args) {
		CalculatorFrame cf = new CalculatorFrame();
		cf.setTitle("Calculator");
		cf.go();
		cf.addAllListeners();
		cf.pack();
		cf.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
		cf.setVisible(true);
	}
}