import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.WindowAdapter;
import java.awt.event.WindowEvent;

//AWT實現
public class AWTCalculation{
    //將視窗中的元件定義為屬性
    private Frame frame;               //定義窗體
    public TextField field;              //定義文字框
 

    private Button[] allButtons;     //定義按鈕陣列

    //在構造方法中建立元件
    public AWTCalculation(){
        frame = new Frame("AWT計算器");
        field = new TextField(20);
        //建立計算機按鈕
        allButtons = new Button[20];
        String str = "←^√±789÷456×123－0.=＋";
        for(int i = 0; i < str.length(); i++){
            allButtons[i] = new
 
 Button(str.substring(i,i+1));
        }
    }

    //初始化視窗，設定佈局
    private void init(){
        //frame的北部面板：預設FlowLayout佈局
        Panel northPanel = new Panel();
        northPanel.add(field);
        //frame的中部面板：設定GridLayout佈局
        Panel centerPanel = new Panel();
        GridLayout grid = new GridLayout(5
 
,4,8,8);
        centerPanel.setLayout(grid);
        //將按鈕新增至中部面板
        for(int i = 0;i < allButtons.length; i++){
            centerPanel.add(allButtons[i]);
        }
        //將面板新增至視窗
        frame.add(northPanel,BorderLayout.NORTH);
        frame.add(centerPanel,BorderLayout.CENTER);
    }

    //設定視窗顯示屬性
    public void showMe(){

        init();
        addEventHandler();
        frame.pack();
        frame.setLocation(500,400);    //窗口出現的位置
        frame.addWindowListener(new WindowCloseHanDler());
        frame.setResizable(false);          //禁止改變視窗大小
        frame.setBackground(Color.PINK);
        frame.setVisible(true);             //設定窗體可見
    }

    //事件監聽器 --- 關閉視窗
    private class WindowCloseHanDler extends WindowAdapter{
        public void windowClosing(WindowEvent e){
            System.exit(0);
        }
    }

    //功能實現部分
    public void addEventHandler(){   //新增監聽
        for(int i = 0; i < allButtons.length; i++){   //按鈕區監聽
            allButtons[i].addActionListener(new CalculateActionHandler());
        }
    }

    //利用內部類繼承ActionListener 實現 ActionPerformed 方法
    class CalculateActionHandler implements ActionListener{

        double op1 = 0,op2 = 0;   //儲存兩個運算元
        String operator = "";
        boolean flag = true;

        @Override
        public void actionPerformed(ActionEvent e) {
            String command = e.getActionCommand();          //按鈕上的文字
            if("0123456789.".indexOf(command) != -1){     //數字按鈕或小數點按鈕
                if(flag){                                 //如果之前處理的是等號，開始組織新的運算元
                    field.setText(command);
                    flag = false;
                }else{                                    //否則繼續拼接運算元
                    field.setText(field.getText()+command);
                }
            }else if( "← ^ √ ± ÷ × － ＋".indexOf(command) != -1 ){           //1取文字框中的資料：第一個運算元
                if(command.equalsIgnoreCase("←")){  //如果是清除，則歸零
                    op1 = 0;
                    field.setText("");
                }else if(command.equalsIgnoreCase("√")) {
                    operator = command;
                    field.setText(command);
                }else {
                    op1 = Double.valueOf(field.getText());
                    //2 記下運算子
                    operator = command;
                    //3 清空文字框
                    field.setText(command);
                }
                flag = true;
            }else if( command.equalsIgnoreCase("=") ){  //等號按鈕
                double res = 0;
                String text = field.getText();
                if(text.length()>0){
                    op2 = Double.valueOf(text);
                    switch(operator) {
                        case "＋":
                            res = op1 + op2;
                            break;
                        case "－":
                            res = op1 - op2;
                            break;
                        case "×":
                            res = op1 * op2;
                            break;
                        case "÷":
                            res = op1 / op2;
                            break;
                        default:
                            break;
                    }
                    field.setText(String.valueOf(res));
                }
                flag = true;
            }
        }
    }
    public static void main(String []args){
        new AWTCalculation().showMe();
    }
}