Just homework

CalculadoraGUI.java

package lpalomin;

import java.awt.Color;
import java.awt.EventQueue;
import java.awt.Font;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

import javax.swing.JFrame;
import javax.swing.AbstractButton;
import javax.swing.JButton;
import javax.swing.JTextArea;

// Context class
public class CalculadoraGUI extends JFrame {

    
    public interface IState {
        public IState transition(String sourceButton, CalculadoraGUI ctx);
    }

    public class SecondOpState implements IState {
        public IState transition(String sourceButton, CalculadoraGUI ctx) {
            if (Character.isDigit(sourceButton.charAt(0))) {
                ctx.operand2 = ctx.operand2 + sourceButton.charAt(0);
                ctx.setDisplay(ctx.operand1 + ctx.operator + ctx.operand2);
                ctx.operand2 = "0";
                return this;
            } else if (sourceButton.equals("=")) {
                ctx.setDisplay(ctx.operand1 + ctx.operator + ctx.operand2 + "=" + ctx.doOperation());
                ctx.resetCalculator();
                return ctx.initState;
            } else if (sourceButton.equals("AC")) {
                ctx.setDisplay("");
                ctx.resetCalculator();
                return ctx.initState;
            }
            return this;
        }
    }

    public class InitState implements IState {
        public IState transition(String sourceButton, CalculadoraGUI ctx) {
            if (Character.isDigit(sourceButton.charAt(0))) {
                    ctx.operand1 = ctx.operand1 + sourceButton.charAt(0);
                    ctx.setDisplay(ctx.operand1);
                    return ctx.firstState;
                } else {
                    ctx.setDisplay("");
                    ctx.resetCalculator();
                    return this;
                }
        }
    }

    public class FirstOpState implements IState {
        public IState transition(String sourceButton, CalculadoraGUI ctx) {
            if (Character.isDigit(sourceButton.charAt(0))) {
                ctx.operand1 = ctx.operand1 + sourceButton.charAt(0);
                ctx.setDisplay(ctx.operand1);
                return this;
            } else if (sourceButton.equals("AC")) {
                ctx.setDisplay("");
                ctx.resetCalculator();
                return ctx.initState;
            } else if (sourceButton.equals("=")) {
                return this;
            } else {
                ctx.operator = sourceButton;
                ctx.setDisplay(ctx.operand1 + ctx.operator);
                return ctx.secondState;
            }
        }
    }

    private JButton[] btnNumbers, btnOperands;
    private JButton erase, solve;
    private JTextArea txtDisplay;
    // Model
    String operand1, operand2, operator;
	IState currentState;
	InitState initState;
	FirstOpState firstState;
	SecondOpState secondState;
    
    public CalculadoraGUI() {
        super();
        this.resetCalculator();
        this.initState = new InitState();
        this.firstState = new FirstOpState();
        this.secondState = new SecondOpState();
        this.currentState = this.initState;
        Controller controller = new Controller(this);
        this.setTitle("Simple Binary Calculator");
        this.resetCalculator();
        this.setBounds(100, 100, 500, 457);
        this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        this.getContentPane().setLayout(null);
        this.getContentPane().setBackground(Color.decode("#5e5d5d"));
        
        // Number Buttons
        this.btnNumbers = new JButton[11];
        
        int cont = 0;
        for(int i = 0; i < 4; i++){
            for(int j = 0; j < 3; j++){
                if(cont >= 10){
                    break;
                }
                this.btnNumbers[cont] = new JButton((cont == 9)? "0":cont+1+"");
                this.btnNumbers[cont].setBounds(40 +j*62, 130+i*62, 60, 60);
                this.btnNumbers[cont].setBackground(Color.decode("#424141"));
                this.btnNumbers[cont].setForeground(Color.white);
                this.btnNumbers[cont].setFocusPainted(false);
                this.btnNumbers[cont].addActionListener(controller);
                this.getContentPane().add(this.btnNumbers[cont++]);
            }
        }
        
        // Operator Buttons
        this.btnOperands = new JButton[5];
        this.btnOperands[0] = new JButton("*");
        this.btnOperands[1] = new JButton("/");
        this.btnOperands[2] = new JButton("+");
        this.btnOperands[3] = new JButton("-");
        this.btnOperands[4] = new JButton("^");
        
        cont = 0;
        for(int i = 0; i < 3; i++){
            for(int j = 0; j < 2; j++){
                if(cont >= this.btnOperands.length){
                    break;
                }
                this.btnOperands[cont].setBounds(300 +j*62, 192+i*62, 60, 60);
                this.btnOperands[cont].setBackground(Color.decode("#424141"));
                this.btnOperands[cont].setForeground(Color.white);
                this.btnOperands[cont].setFocusPainted(false);
                this.btnOperands[cont].addActionListener(controller);
                this.getContentPane().add(this.btnOperands[cont++]);
            }
        }
        
        // AC and Equal Buttons
        this.erase = new JButton("AC");
        this.erase.setBounds(362, 130, 60, 60);
        this.erase.setBackground(Color.decode("#424141"));
        this.erase.setForeground(Color.white);
        this.erase.setFocusPainted(false);
        this.erase.addActionListener(controller);
        this.getContentPane().add(this.erase);
        
        this.solve = new JButton("=");
        this.solve.setBounds(362, 316, 60, 60);
        this.solve.setBackground(Color.decode("#424141"));
        this.solve.setForeground(Color.white);
        this.solve.setFocusPainted(false);
        this.solve.addActionListener(controller);
        this.getContentPane().add(this.solve);
        
        // TextField Display
        
        this.txtDisplay = new JTextArea();
        this.txtDisplay.setBounds(43, 25, 400, 85);
        this.txtDisplay.setBackground(Color.decode("#ffffff"));
        this.txtDisplay.setFont(new Font("normal", Font.BOLD, 28));
        getContentPane().add(this.txtDisplay);
        this.txtDisplay.setEditable(false);
        
        this.setVisible(true);
    }
    
    public void setDisplay(String text)
    {
    	this.txtDisplay.setText(text);
    }
    
    protected void resetCalculator()
    {
    	this.operand1 = "";
    	this.operand2 = "";
    }

    protected String doOperation()
    {
        int oper1 = Integer.valueOf(this.operand1);
        int oper2 = Integer.valueOf(this.operand2);
        switch(this.operator) {
        case "+":
            return Integer.toString(oper1 + oper2);
        case "-":
            return Integer.toString(oper1 - oper2);
        case "*":
            return Integer.toString(oper1 * oper2);
        case "/":
            if(oper2 == 0) {
                return "INFINITY";
            } else {
                return Integer.toString(oper1 / oper2);
            }
        case "^":
            return Integer.toString(oper1 ^ oper2);
        }
        return "???";
    }
    
    static class Controller implements ActionListener {
    	CalculadoraGUI view;
    	
    	public Controller(CalculadoraGUI view) {
    		this.view = view;
    	}
    	
    	public void actionPerformed(ActionEvent e)
    	{
    		String sourceButton = ((JButton) e.getSource()).getText();
			this.view.currentState = this.view.currentState.transition(sourceButton, this.view);
    	}
    }
    
    public static void main(String[] args) {
        new CalculadoraGUI();
    }
}