第三次作业

                 组员：杨家堂，吴金

• 题目

          请编写一个能自动生成小学四则运算题目的 “软件”。

          让程序能接受用户输入答案，并进行计算。 

          最后给出正确的答案。

• 需求分析

        - 基本功能

           - 显示每次测试题目数量

           - 用户可以逐个题目解答

 

        - 扩展功能

           -用户答题结束以后，程序可以显示用户答题所用的时间

• 代码实现
   

  import javax.swing.*; 
  import java.awt.*; 
  import java.awt.event.*; 
  
  public class Calculator extends JFrame implements ActionListener 
  { 
      private boolean dotExist, operated, equaled; // 帮助运算的布尔变量 
      private double storedNumber; // 目前的结果 
      private char lastOperator; // 表示上一运算符 
      private JTextField operation; // 结果栏 
      private JButton dot, plus, minus, multi, div, sqrt, equal, changePN, clear; // 运算符 
      private JButton[] numbers; // 数字 
      
      // 构造者 
      public Calculator() 
      { 
          setTitle("Calculator"); 
          // 初始化变量 
          dotExist = false; // 表示当前的数是否有小数点 
          operated = false; // 表示任意运算符是否被按下 
          equaled = false; // 表示等号是否被按下 
          storedNumber = 0; 
          lastOperator = '?'; 
          // 初始化窗口变量 
          operation = new JTextField("0"); 
          operation.setEditable(false); 
          numbers = new JButton[10]; 
          for (int i = 0; i < 10; i++) 
          numbers[i] = new JButton("" + i); 
          dot = new JButton("."); 
          plus = new JButton("+"); 
          minus = new JButton("-"); 
          multi = new JButton("*"); 
          div = new JButton("/"); 
          sqrt = new JButton("√"); 
          equal = new JButton("="); 
          changePN = new JButton("±"); 
          clear = new JButton("AC"); 
          // 将窗口物体放入窗口 
          GridBagLayout layout = new GridBagLayout(); 
          getContentPane().setLayout(layout); 
          addComponent(layout, operation, 0, 0, 4, 1); 
          addComponent(layout, numbers[1], 1, 0, 1, 1); 
          addComponent(layout, numbers[2], 1, 1, 1, 1); 
          addComponent(layout, numbers[3], 1, 2, 1, 1); 
          addComponent(layout, numbers[4], 2, 0, 1, 1); 
          addComponent(layout, numbers[5], 2, 1, 1, 1); 
          addComponent(layout, numbers[6], 2, 2, 1, 1); 
          addComponent(layout, numbers[7], 3, 0, 1, 1); 
          addComponent(layout, numbers[8], 3, 1, 1, 1); 
          addComponent(layout, numbers[9], 3, 2, 1, 1); 
          addComponent(layout, dot, 4, 0, 1, 1); 
          addComponent(layout, numbers[0], 4, 1, 1, 1); 
          addComponent(layout, sqrt, 4, 2, 1, 1); 
          addComponent(layout, plus, 1, 3, 1, 1); 
          addComponent(layout, minus, 2, 3, 1, 1); 
          addComponent(layout, multi, 3, 3, 1, 1); 
          addComponent(layout, div, 4, 3, 1, 1); 
          addComponent(layout, equal, 5, 0, 2, 1); 
          addComponent(layout, changePN, 5, 2, 1, 1); 
          addComponent(layout, clear, 5, 3, 1, 1); 
      } 
   // 对按钮进行反应的方法 
      public void actionPerformed(ActionEvent e) 
      { 
          JButton btn = (JButton)e.getSource(); 
          if (btn == clear) 
          { 
              operation.setText("0"); 
              dotExist = false; 
              storedNumber = 0; 
              lastOperator = '?'; 
          } 
          else if (btn == equal) 
          { 
              operate('='); 
              equaled = true; 
          } 
          else if (btn == plus) 
          { 
              operate('+'); 
              equaled = false; 
          } 
          else if (btn == minus) 
          { 
              operate('-'); 
              equaled = false; 
          } 
          else if (btn == multi) 
          { 
              operate('*'); 
              equaled = false; 
          } 
          else if (btn == div) 
          { 
              operate('/'); 
              equaled = false; 
          } 
          else if (btn == changePN) 
          { 
              operate('p'); 
              operate('='); 
              equaled = true; 
          } 
          else if (btn == sqrt) 
          { 
              operate('s'); 
              operate('='); 
              equaled = true; 
          } 
          else 
          { 
              if (equaled) 
              storedNumber = 0; 
              for (int i = 0; i < 10; i++) 
              if (btn == numbers[i]) 
              { 
                  if (operation.getText().equals("0")) 
                      operation.setText("" + i); 
                  else if(! operated) 
                      operation.setText(operation.getText() + i); 
                  else 
                  { 
                      operation.setText("" + i); 
                      operated = false; 
                  } 
              } 
              if (btn == dot && ! dotExist) 
              { 
                  operation.setText(operation.getText() + "."); 
                  dotExist = true; 
              } 
          } 
      } 
      // 进行运算的方法 
      private void operate(char operator) 
      { 
          double currentNumber = Double.valueOf(operation.getText()).doubleValue(); 
          if (lastOperator == '?') 
          storedNumber = currentNumber; 
          else if (lastOperator == '+') 
          storedNumber += currentNumber; 
          else if (lastOperator == '-') 
          storedNumber -= currentNumber; 
          else if (lastOperator == '*') 
          storedNumber *= currentNumber; 
          else if (lastOperator == '/') 
          storedNumber /= currentNumber; 
          else if (lastOperator == 'p') 
          storedNumber *= -1; 
          else if (lastOperator == 's') 
          storedNumber = Math.sqrt(currentNumber); 
          else if (lastOperator == '=' && equaled) 
          storedNumber = currentNumber; 
          operation.setText("" + storedNumber); 
          operated = true; 
          lastOperator = operator; 
      } 
      
      // 快捷使用GridBagLayout的方法 
      private void addComponent(GridBagLayout layout, Component component, int row, int col, int width, int height) 
      { 
          GridBagConstraints constraints = new GridBagConstraints(); 
          constraints.fill = GridBagConstraints.BOTH; 
          constraints.insets = new Insets(10, 2, 10, 2); 
          constraints.weightx = 100; 
          constraints.weighty = 100; 
          constraints.gridx = col; 
          constraints.gridy = row; 
          constraints.gridwidth = width; 
          constraints.gridheight = height; 
          layout.setConstraints(component, constraints); 
          if (component instanceof JButton) 
          ((JButton)component).addActionListener(this); 
          getContentPane().add(component); 
      } 
      
      // 主方法初始化并显示窗口 
      public static void main(String[] args) 
      { 
          Calculator calc = new Calculator(); 
          calc.setSize(290, 400); 
          calc.setVisible(true); 
      } 
  }