Taking input using bufferedreader

Question

I want to take input in the format: -prize 45

This is my code

static double prize_input(String list[]) throws IOException{
    boolean flag=false;
    double p=0;
    while(true){
        if(list.length!=2 || ( list[0].compareTo("-prize")!=0 ) ){
            System.out.println("usage: -prize <Itemprize>");
            flag=true;
        }
        else
        {
                try{
                    p=Double.parseDouble(list[1]);
                    flag=false;
                }
                catch(Exception e){
                    flag=true;
                }
        }
        if(!flag)
            return p;
        else
            list=br.readLine().split(" ");
    }
  }

When I input: -prize abc where second argument is also a string it prompts me for another enter key from user instead of display the appropriate message. Please tell me what am I missing and how should I correct it.

Answer 1

当你正在接受（true）作为一个循环条件时，你的条件就是你的状态，并且你正在接受一个输入，其中循环将永远存在，并且缓冲读取器等待下一行被分割。

Answer 2

usage: -prize <Itemprize> will be printed only if this condition will fail

if (list.length != 2 || (list[0].compareTo("-prize") != 0)) 

so only if

• user didn't provided two elements,
• and if first element is not -prize .

Since for -price aaa both conditions are fulfilled so user will not see this info, but flag representing correctness of data will be set to false while failed parsing second parameter, so in

else
    list = br.readLine().split(" ");

program will be waiting for new data form

To improve user experience you should print usage info right before reading new data from user, so try moving line

System.out.println("usage: -prize <Itemprize>");

right before br.readLine()

else{
    System.out.println("usage: -prize <Itemprize>");
    list = br.readLine().split(" ");
}