//父類代碼。
public?abstract?class?shape?{
	public?abstract?void?length();
	public?abstract?void?square();
}
//長方形子類代碼。
public?class?rectangle?extends?shape?{
	Scanner?scan1=new??Scanner(System.in);
	int?l=scan1.nextInt();
	Scanner?scan2=new??Scanner(System.in);
	int?w=scan2.nextInt();
		public?void?length()?{
		int??length=2*(l+w);
		System.out.println("長方形的周長為："+length);
	}
	public?void?square()?{
		int??square=w*l;
		System.out.println("長方形的面積為："+square);
	}
}
//圓形子類代碼。
public?class?circle?extends?shape?{
	Scanner?scan1=new??Scanner(System.in);
	double?r=scan1.nextDouble();
	public?void?length()?{
		double?length=2*3.14*r;
		System.out.println("圓形的周長為："+length);
	}
	public?void?square()?{
		double?square=3.14*r*r;
		System.out.println("圓形的面積為："+square);
	}
}
//測(cè)試類代碼。
public?class?test?{
	public?static?void?main(String[]?args)?{
		System.out.println("請(qǐng)輸入您要查詢的圖形類型：1代表長方形，2代表圓形。");
		Scanner?input?=new?Scanner(System.in);
		int?num=input.nextInt();
		switch?(num)?{
		case?1:
			System.out.println("請(qǐng)依次輸入長方形的長度和寬度：");
			shape?shp1=new?rectangle();
			shp1.length();
			shp1.square();			
			break;
		case?2:
			System.out.println("請(qǐng)輸入圓形的半徑：");
			shape?shp2=new?circle();
			shp2.length();
			shp2.square();			
			break;
		default:
			System.out.println("您輸入的數(shù)值有誤，請(qǐng)重新輸入。");
		}
	}
}

我想要的改進(jìn)是：在用戶輸入其他數(shù)值顯示錯(cuò)誤后，不用重新運(yùn)行程序就可以接著接著重新輸入，直到是1或者2