Java Example

• commands

  • commands/Command.java

    package refactoring_guru.command.example.commands;
    
    import refactoring_guru.command.example.editor.Editor;
    
    public abstract class Command {
        public Editor editor;
        private String backup;
    
        Command(Editor editor) {
            this.editor = editor;
        }
    
        void backup() {
            backup = editor.textField.getText();
        }
    
        public void undo() {
            editor.textField.setText(backup);
        }
    
        public abstract boolean execute();
    }

  • commands/CommandHistory.java

    package refactoring_guru.command.example.commands;
    
    import java.util.Stack;
    
    public class CommandHistory {
        private Stack<Command> history = new Stack<>();
    
        public void push(Command c) {
            history.push(c);
        }
    
        public Command pop() {
            return history.pop();
        }
    
        public boolean isEmpty() { return history.isEmpty(); }
    }

  • commands/CopyCommand.java

    package refactoring_guru.command.example.commands;
    
    import refactoring_guru.command.example.editor.Editor;
    
    public class CopyCommand extends Command {
    
        public CopyCommand(Editor editor) {
            super(editor);
        }
    
        @Override
        public boolean execute() {
            editor.clipboard = editor.textField.getSelectedText();
            return false;
        }
    }

  • commands/CutCommand.java

    package refactoring_guru.command.example.commands;
    
    import refactoring_guru.command.example.editor.Editor;
    
    public class CutCommand extends Command {
    
        public CutCommand(Editor editor) {
            super(editor);
        }
    
        @Override
        public boolean execute() {
            if (editor.textField.getSelectedText().isEmpty()) return false;
    
            backup();
            String source = editor.textField.getText();
            editor.clipboard = editor.textField.getSelectedText();
            editor.textField.setText(cutString(source));
            return true;
        }
    
        private String cutString(String source) {
            String start = source.substring(0, editor.textField.getSelectionStart());
            String end = source.substring(editor.textField.getSelectionEnd());
            return start + end;
        }
    }

  • commands/PasteCommand.java

    package refactoring_guru.command.example.commands;
    
    import refactoring_guru.command.example.editor.Editor;
    
    public class PasteCommand extends Command {
    
        public PasteCommand(Editor editor) {
            super(editor);
        }
    
        @Override
        public boolean execute() {
            if (editor.clipboard == null || editor.clipboard.isEmpty()) return false;
    
            backup();
            editor.textField.insert(editor.clipboard, editor.textField.getCaretPosition());
            return true;
        }
    }

• editor/Editor.java

  package refactoring_guru.command.example.editor;
  
  import refactoring_guru.command.example.commands.*;
  
  import javax.swing.*;
  import java.awt.*;
  import java.awt.event.ActionEvent;
  import java.awt.event.ActionListener;
  
  public class Editor {
      public JTextArea textField;
      public String clipboard;
      private CommandHistory history = new CommandHistory();
  
      public void init() {
          JFrame frame = new JFrame("Text editor (type & use buttons, Luke!)");
          JPanel content = new JPanel();
          frame.setContentPane(content);
          frame.setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
          content.setLayout(new BoxLayout(content, BoxLayout.Y_AXIS));
          textField = new JTextArea();
          textField.setLineWrap(true);
          content.add(textField);
          JPanel buttons = new JPanel(new FlowLayout(FlowLayout.CENTER));
          JButton ctrlC = new JButton("Ctrl+C");
          JButton ctrlX = new JButton("Ctrl+X");
          JButton ctrlV = new JButton("Ctrl+V");
          JButton ctrlZ = new JButton("Ctrl+Z");
          Editor editor = this;
          ctrlC.addActionListener(new ActionListener() {
              @Override
              public void actionPerformed(ActionEvent e) {
                  executeCommand(new CopyCommand(editor));
              }
          });
          ctrlX.addActionListener(new ActionListener() {
              @Override
              public void actionPerformed(ActionEvent e) {
                  executeCommand(new CutCommand(editor));
              }
          });
          ctrlV.addActionListener(new ActionListener() {
              @Override
              public void actionPerformed(ActionEvent e) {
                  executeCommand(new PasteCommand(editor));
              }
          });
          ctrlZ.addActionListener(new ActionListener() {
              @Override
              public void actionPerformed(ActionEvent e) {
                  undo();
              }
          });
          buttons.add(ctrlC);
          buttons.add(ctrlX);
          buttons.add(ctrlV);
          buttons.add(ctrlZ);
          content.add(buttons);
          frame.setSize(450, 200);
          frame.setLocationRelativeTo(null);
          frame.setVisible(true);
      }
  
      private void executeCommand(Command command) {
          if (command.execute()) {
              history.push(command);
          }
      }
  
      private void undo() {
          if (history.isEmpty()) return;
  
          Command command = history.pop();
          if (command != null) {
              command.undo();
          }
      }
  }

• Demo.java

  package refactoring_guru.command.example;
  
  import refactoring_guru.command.example.editor.Editor;
  
  public class Demo {
      public static void main(String[] args) {
          Editor editor = new Editor();
          editor.init();
      }
  }