//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);
????}
}
//測試類代碼。
public?class?test?{
????public?static?void?main(String[]?args)?{
????????System.out.println("請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("您輸入的數值有誤，請重新輸入。");
????????}
????}
}

這是我剛發布的問題里面的代碼，能運行，只是有點小瑕疵：一次只能計算一種圖形，下一次需要重新運行才可以。