Question

我是一名新程序员，我收到的错误在我的ShapeApp类中找不到符号。我的错误是

System.out.println（“矩形的当前长度为：”+ r1.getLength（））; ^ 符号：变量r1 location：class ShapeApp

请尝试以更简单的方式解释它。非常感谢，我的代码如下。

public class Rectangle
{
protected double length;
protected double width;

public Rectangle() {  }
public Rectangle(double l,double w)
{
   length = l;
   width = w;
}
public void setLength(double l) {length = l;}
public double getLength() {return length;}

public void setWidth(double w) {width = w;}
public double getWidth() {return width;}

public double findArea() {return length * width;}

public String toString() 
{
   return "\tLength " + length + "\tWidth " + width;
}
}



public class Box extends Rectangle
{
private double height;

public Box() {   }
public Box(double l,double w,double h)
{
   super(l,w); 
   height = h;
}
public void setHeight(double h) {height = h;}
public double getHeight() {return height;}

public double findArea() {return ((super.findArea() * 2) + (2 * height * width) + (2 * height * length));}
public double findVolume() {return super.findArea() * height;}

public String toString()
{
return super.toString() + "\tHeight " + height;
}
}





import java.util.*;

public class ShapeApp
{
   public static void main(String[] args)
   { 
   Rectangle r1 = new Rectangle(20,10);
   Box b1 = new Box(10,5,5); 

   int options;

   Scanner input = new Scanner(System.in);

   do{
      displayMenu();
      options = input.nextInt();

            switch(options)
            {
            case 1: changeRecL();
                    break;
            case 2: changeBoxL();
                    break;
            case 3: changeBoxH();
                    break; 
            case 4: displayAreaRec();
                    break;
            case 5: displaySaBox();
                    break; 
            case 6: displayVoBox();
                    break;            
            case 0: System.out.println("Exiting Program");
                    break;
            default: System.out.println("Invalid Option. ");
            }
      }while(options != 0);    
   }

   public static void displayMenu()
   {
   System.out.println("-------------------------------MENU-------------------------------");
   System.out.println("[1] Change the length of rectangle");
   System.out.println("[2] Change the length of box");
   System.out.println("[3] Change the height of box");
   System.out.println("[4] Display the area of rectangle");
   System.out.println("[5] Display the surface area of box");
   System.out.println("[6] Display the volume of box");
   System.out.println("[0] Exit");
   System.out.println("------------------------------------------------------------------");   
   System.out.println("Enter your option:");
   }

   public static void changeRecL()
   {
   Scanner input = new Scanner(System.in);

   System.out.println("Current length of rectangle is: " + r1.getLength());
   System.out.println("Enter new length of rectangle: ");

   double nlength = input.nextDouble();

   r1.setLength(nlength);
   }

   public static void changeBoxL()
   {

   }

   public static void changeBoxH()
   {

   }

   public static void displayAreaRec()
   {

   }

   public static void displaySaBox()
   {

   }

   public static void displayVoBox()
   {

   }

}

Answer 1

那是因为你没有在你的方法changeRecL中定义r1。

也许您想将r1从main传递给您的方法，如下所示：

case 1: changeRecL(r1);

并接受R1如下：

public static void changeRecL(Rectangle r1)

Answer 2

定义对象类时，可以将类的多个实例作为对象。不仅有一个矩形r1。如果你只想为一切使用一个矩形，你应该实现一个Singleton类。

public class Rectangle {
   double len;
   double wid;
   private static Rectangle instance = null;
   protected Rectangle() {
      // Exists only to defeat instantiation.
   }
   public static Rectangle getInstance() {
      if(instance == null) {
         instance = new Rectangle();
      }
      return instance;
   }
public static void setLen (double l){
      len = l;
}
public static double getLen (){
      return len;
    }
public static void setWid (double w){
      wid = w;
    }
public static double getWid(){
      return wid;
    }
}

但是，就像@almas_shaikh所说的那样，将对象实例传递给方法更容易。

另外，让我提醒您，java length一词用于确定数组和其他对象的大小，如getLength()方法。您应该使用另一个名称来设置长度属性和方法以避免冲突。

在方法changeRecL中找不到符号但在main方法中声明

2 个答案: