7-2作业中如何实现0/1的选择，避免输入非1或0的数字？

  while (flag) {
                        Scanner sc2 = new Scanner(System.in);
                        int n2 = sc2.nextInt();
                        switch (n2) {
                            case 1:
                                ms.notice();
                                break;
                            case 2:
                                System.out.println("表演结束");
                                flag = false;
                                break;
                        }
                    }

你的代码里用的是1，2 啊

另外，表演结束直接用return就行

public class TestAnimal {
    //表演的菜单显示
    public void notice() {
        System.out.println("************欢迎来到太阳马戏团***************");
        System.out.println("*******请选择表演者***********");
        System.out.println("*********   1、熊   ***************");
        System.out.println("*********   2、狮子 ***************");
    }

    // 表演是否继续判断
    public void notice2() {
        System.out.println("************是否继续观看（0/1）**************");
    }

    public static void main(String[] agrs) {
        TestAnimal ms = new TestAnimal();
        boolean flag = true;
        Scanner sc = new Scanner(System.in);
        int[] a = new int[5];
        while (flag) {
            ms.notice();
            int n = sc.nextInt();
            switch (n) {
                case 1:
                    // Bear
                    Animal a1 = new Bear("Bill", 1);
                    if (a1 instanceof Bear) {
                        Bear temp = (Bear) a1;
                        temp.atc();
                        temp.skill();
                        temp.love();
                    }break;
                case 2:
                    //Lion
                    Animal a2 = new Lion("Lain", 2, "灰色", "公狮");
                    if (a2 instanceof Lion) {
                        Lion temp2 = (Lion) a2;
                        temp2.atc();
                        temp2.skill();
                        temp2.love();
                    }break;
                default:
                    ms.notice2();
                    while (flag) {
                        Scanner sc2 = new Scanner(System.in);
                        int n2 = sc2.nextInt();
                        switch (n2) {
                            case 1:
                                ms.notice();
                                break;
                            case 2:
                                System.out.println("表演结束");
                                flag = false;
                                break;
                        }
                    }
            }
        }

    }
}