equationmainclass.java

通过对二次方程系数的检验判断并计算方程的根

import java.awt.*; 
import java.awt.event.*;  
class SquareEquation  
{   double a,b,c; 
   double root1,root2; 
   public void setA(double a) 
   {   this.a=a; 
   } 
   public void setB(double b) 
   {   this.b=b; 
   } 
   public void setC(double c) 
   {   this.c=c; 
   } 
public double getRootOne() throws NoRealRootException,NoSquareEquationException 
   {   if(a!=0) 
      {   double disk=b*b-4*a*c; 
         if(disk>=0) 
         {   root1=(-b+Math.sqrt(disk))/(2*a); 
          }  
         else 
         {   throw new NoRealRootException("没有实根");  
          } 
      } 
      else 
      {   throw new NoRealRootException("不是二次方程");  
      } 
      return root1; 
   }  
public double getRootTwo() throws NoRealRootException,NoSquareEquationException 
   {   if(a!=0) 
      {   double disk=b*b-4*a*c; 
         if(disk>=0) 
         {   root2=(-b-Math.sqrt(disk))/(2*a); 
          }  
         else 
         {   throw new NoRealRootException("没有实根");  
          } 
      } 
      else 
      {   throw new NoRealRootException("不是二次方程");  
      } 
      return root2; 
   }  
} 
class NoRealRootException extends Exception 
{   String message; 
   NoRealRootException(String s) 
   {   message=s; 
   } 
   public String getMessage() 
   {   return message; 
   } 
} 
class NoSquareEquationException extends Exception 
{   String message; 
   NoSquareEquationException(String s) 
   {   message=s; 
   } 
   public String getMessage() 
   {   return message; 
   } 
} 
class EquationFrame extends Frame implements ActionListener 
{   SquareEquation equation; 
   TextField textA,textB,textC; 
   TextArea showRoots; 
   Button controlButton; 
   public EquationFrame() 
   {   equation=new SquareEquation(); 
      textA=new TextField(8);    
      textB=new TextField(8); 
      textC=new TextField(8); 
      showRoots=new TextArea(); 
      controlButton=new Button("确定"); 
      Panel pNorth=new Panel(); 
      pNorth.add(new Label("二次项系数:")); 
      pNorth.add(textA); 
      pNorth.add(new Label("一次项系数:")); 
      pNorth.add(textB); 
      pNorth.add(new Label("常数项系数:")); 
      pNorth.add(textC);  
      pNorth.add(controlButton);  
      controlButton.addActionListener(this);//当前窗口作为controlButton的ActionEvent事件的监视器 
      add(pNorth,BorderLayout.NORTH); 
      add(showRoots,BorderLayout.CENTER); 
      setBounds(100,100,630,160); 
      setVisible(true); 
      validate(); 
      addWindowListener(new WindowAdapter() 
                     {   public void windowClosing(WindowEvent e) 
                        {   System.exit(0); 
                        } 
                     }); 
   } 
   public void actionPerformed(ActionEvent e) 
   {   try 
      {   double a=Double.parseDouble(textA.getText());   //textA调用方法获取其中的文本 
         double b=Double.parseDouble(textB.getText()); //textB调用方法获取其中的文本 
         double c=Double.parseDouble(textC.getText());   // textC调用方法获取其中的文本 
         double d=Math.sqrt(b*b-4*a*c);
         equation.setA(a); 
         equation.setB(b); 
         equation.setC(c); 
         textA.setText(""+a); 
         textB.setText(""+b); 
         textC.setText(""+c); 
         showRoots.append("\n -b="+-b+"  b*b-4*a*c的算术平方根为:"+d+"  2a="+2*a);
         showRoots.append("\n 根："+equation.getRootOne()); 
         showRoots.append("   根："+equation.getRootTwo()); 
      }  
      catch(Exception ex) 
      {   showRoots.append("\n"+ex+"\n"); 
      } 
   } 
} 
  
public class EquationMainClass 
{   public static void main(String args[]) 
   {   EquationFrame frame=new EquationFrame(); 
   } 
}