• 代码我还没有调试过，你自己参看一下，错了的改过来

public class BorrowBook {

    public static String books[] = {"shengjing", "lunyu", "xiaorenshu"};

    //程序入口
    public static void main(String[] args) {

      try {
          BookManager();
      }catch (Exception e){
          System.out.println(e.getMessage());
      }
    }

    //图书管理
    private static void BookManager() {
        while (true) {
            Scanner scanner = new Scanner(System.in);
            System.out.println("输入命令1-按照名称查找图书；2-按照序号查找图书");
            if (scanner.hasNextInt()) {
                int command = scanner.nextInt();
                switch (command) {
                    case 1:
                        queryByBookName(scanner);
                        break;
                    case 2:
                        queryByBookIndex(scanner);
                        break;
                    default:
                        System.out.println("命令输入错误，请根据提示输入数字命令");
                }
            }
        }
    }

    //根据名字查询
    private  static  void queryByBookIndex(Scanner scanner) {
        if (scanner.hasNextInt()) {
            int index= scanner.nextInt();
            if (index <= books.length && index > 0) {
                System.out.println("book:" + books[index - 1]);
            } else {
                System.out.println("图书不存在.");
            }
        }
    }

    //根据 编号查询
    private  static  void queryByBookName(Scanner scanner) {
        System.out.println("请输入图书名称：");
        String bookName = scanner.next();
        for (int a = 0; a < books.length; a++) {
            if (bookName.equals(books[a])) {
                System.out.println("book:" + bookName);
                System.exit(0);
            }
        }
    }
}

• 一： 提问时麻烦把代码整理一下，方便别人看

• 二：package stduy; 请命名规范 如 com.stduy

• 三：一个方法 代码不要 超过 80行 你这个已经超出了，写的太难看，方法长了 应该拆分多个方法

• 四：if,for,while 下面不要套太多的 （条件，循环，判断），影响代码可读写

• 五：最上层 一般要 try catch 不然程序就挂了

package stduy;


import java.util.Scanner;


public class BorrowBook {

    public static String books[] = {"shengjing", "lunyu", "xiaorenshu"};

    public static void main(String[] args) {

// TODO 自动生成的方法存根

        while (true) {

            Scanner x = new Scanner(System.in);

            System.out.println("输入命令1-按照名称查找图书；2-按照序号查找图书");

            if (x.hasNextInt()) {

                int y = x.nextInt();

                if (y == 1) {

                    System.out.println("请输入图书名称：");

                    String z = x.next();

                    for (int a = 0; a < books.length; a++) {

                        if (z.equals(books[a])) {

                            System.out.println("book:" + z);

                            System.exit(0);

                        } else {

                            continue;

                        }

                    }

                    System.out.println("图书不存在.");

                    continue;

                } else if (y == 2) {

                    System.out.println("请输入图书序号：");

                    if (x.hasNextInt()) {

                        int w = x.nextInt();

                        if (w <= books.length && w > 0) {

                            System.out.println("book:" + books[w - 1]);

                            System.exit(0);

                        } else {

                            System.out.println("图书不存在.");

                            continue;

                        }


                    } else {

                        System.out.println("图书不存在");

                    }

                    continue;

                } else {

                    System.out.println("命令输入错误，请根据提示输入数字命令");

                    continue;

                }

            } else {

                System.out.println("命令输入错误，请根据提示输入数字命令");

                continue;

            }

        }

    }

}