从键盘读入多行字符串，统计输出字符串行数。输入“exit”，退出程序。？

package Jishuhang_wangdong;

import java.util.Scanner;

public class Jishuhang_wangdong {

    public static void main(String[] args) {
        // TODO Auto-generated method stub

        System.out.println("请输入字符串");
        Scanner sc = new Scanner(System.in);
        String str = null;
        int a=0;
        while((str=sc.nextLine())!=null){
             a=a+1;


        System.out.println("行数:"+a);
        break;
        }
        while (true){
            System.out.println("请输入退出命令");
            String str1 = sc.nextLine();//读入一行字符串
            if(str1.equals("exit")) {
                System.out.println("程序退出");
                break;//退出循环

        }
    }

    }
        }

package Jishuhang_wangdong;

import java.util.Scanner;

public class Jishuhang_wangdong {

    public static void main(String[] args) {
        // TODO Auto-generated method stub

        System.out.println("请输入字符串");
        Scanner sc = new Scanner(System.in);
        String str = null;
        int a=0;
        while((str=sc.nextLine())!=null){
             a=a+1;
            if(str.equals("exit")) {
                System.out.println("程序退出");
                break;//退出循环 }
                                }

        System.out.println("行数:"+a);
        break;
        }

    }