Java錯誤，表達式開始非法

Question

我收到這樣的錯誤消息：它的表達式開頭是非法的，並且幾乎將每一行都顯示為問題。 我在這里缺少什么幫助嗎？

public abstract class Shapes
{
public static void main(String[] args)
{
    protected final double pi=3.14;

    //varible pi is delcared as constant

     protected double radius;
     protected double height;

     public Shapes (double gRadius,double gHeight)  
     {
        //sets radius, height variables to parameter values
        radius=gRadius;
        height=gHeight;
     }

          abstract public double getCircumference();
          abstract public double getTotalSurfaceArea();
          abstract public double getVolume();
}
}

Answer 1

您的問題是您將類的內容放入了main方法中。

只需移動您的主要：

public abstract class Shapes
{
    protected final double pi=3.14;

    //varible pi is delcared as constant

     protected double radius;
     protected double height;

     public Shapes (double gRadius,double gHeight)  
     {
        //sets radius, height variables to parameter values
        radius=gRadius;
        height=gHeight;
     }

     abstract public double getCircumference();
     abstract public double getTotalSurfaceArea();
     abstract public double getVolume();

     public static void main(String[] args)
     {
     }
}

Answer 2

變量 ， 方法和構造函數必須在要為其聲明類的類中聲明，而不是在main方法內部聲明，因此將所有Variable ， 方法和構造函數聲明從main方法移到該類內部，那么您的代碼將正常工作！

public abstract class Shapes{

protected final double pi=3.14;

//varible pi is delcared as constant

 protected double radius;
 protected double height;

 public Shapes (double gRadius,double gHeight)  
 {
    //sets radius, height variables to parameter values
    radius=gRadius;
    height=gHeight;
 }

 abstract public double getCircumference();
 abstract public double getTotalSurfaceArea();
 abstract public double getVolume();

 public static void main(String[] args)
 {
 }

}

Answer 3

您應該只在類內部聲明所有變量，方法。所有對象的創建和調用方法都必須在main（）方法中進行。就像這個公共抽象類Shapes {protected final double pi = 3.14;

 protected double radius;
 protected double height;

 public Shapes (double gRadius,double gHeight)  
 {
    //sets radius, height variables to parameter values
    radius=gRadius;
    height=gHeight;
 }

 abstract public double getCircumference();
 abstract public double getTotalSurfaceArea();
 abstract public double getVolume();
public static void main(String args[])
{
} 
}