Java：变量已在方法中定义

Java: Variable is already defined in method

提问by user3547815

I am trying to make a program which makes a random number between 1000-9999 with no repeating numbers. The rules are I have to label the random number as a String, and then use a while loop to figure out if any of the numbers repeat.

我正在尝试制作一个程序，该程序在 1000-9999 之间生成一个没有重复数字的随机数。规则是我必须将随机数标记为字符串，然后使用 while 循环来确定是否有任何数字重复。

//generating random number
double answer1 = (Math.random() * 9000)+1000;

//converting answer
int answer2 = (int)answer1;
String answer = answer2 + " ";

//Labeling arrays
answer.toCharArray();

//**NEW** checking random number
while (answer.charAt(0) == answer.charAt(0)
       || answer.charAt(0) == answer.charAt(1)
       || answer.charAt(0) == answer.charAt(2)
       || answer.charAt(0) == answer.charAt(3)
       || answer.charAt(1) == answer.charAt(1)
       || answer.charAt(1) == answer.charAt(2)
       || answer.charAt(1) == answer.charAt(3)
       || answer.charAt(2) == answer.charAt(2)
       || answer.charAt(2) == answer.charAt(3)
       || answer.charAt(3) == answer.charAt(3)); //you have my apologies
{
    ////generating random number
    double answer1 = (Math.random() * 9000)+1000;

    //converting answer
    int answer2 = (int)answer1;
    String answer = answer2 + "
}

I know the while parameters are extremely long, but it was necessary to make sure none of the numbers repeated. I assumed that I could regenerate a new random number and test it again in the while loop, but I get the error that variables answer1, answer, and answer2 are already defined in my main method. Does anyone have a tip as to what I can do to generate a new random number until none of the numbers repeat?

我知道 while 参数非常长，但有必要确保没有重复的数字。我假设我可以重新生成一个新的随机数并在 while 循环中再次测试它，但是我收到错误，变量 answer1、answer 和 answer2 已经在我的主要方法中定义。有没有人知道我可以做些什么来生成一个新的随机数，直到没有一个数字重复？

回答by PressingOnAlways

I am not sure if this is the main issue (you may have more than one), but a ; should not terminate a while statement. It should be while (..) { }, not while (..); { }.

我不确定这是否是主要问题（您可能有多个），但是 ; 不应终止 while 语句。应该是while (..) { }，不是while (..); { }。

As for your error about redefinition, you cannot define the variable again that was already defined in a larger scope. For this instance, line 2, int answer2 = (int) answer1already defined answer2. In the while loop, you just have to use the variable again and you do not need to define it. So it should be:

至于你关于重定义的错误，你不能再次定义已经在更大范围内定义的变量。对于这个例子，第 2 行，int answer2 = (int) answer1已经定义了 answer2。在 while 循环中，您只需要再次使用该变量，而无需定义它。所以应该是：

  while (...)
  {
     ////generating random number
     answer1 = (Math.random() * 9000)+1000;

     //converting answer
     answer2 = (int)answer1;
     answer = answer2 + " ";
  }

回答by nablex

There is so much wrong with this question that it boggles the mind.

这个问题有很多错误，令人难以置信。

However specifically: you are redefining variables in the same scope which is not allowed.

但具体来说：您在同一范围内重新定义变量，这是不允许的。

回答by Ankit Lamba

You've already define your variable answer2in line 2, and in your while loop you are trying to redefine the variable answer2, i.e:

你已经定义了你的变量answer2中line 2，并在你的while循环，你正在试图重新定义变量answer2，即：

int answer2 = (int)answer1;

You can do it like :

你可以这样做：

answer2 = (int)answer1;

回答by Rishi Dwivedi

 answer.toCharArray(); // here you use answer variable

and than your loop closed

而不是你的循环关闭

while(conditon);

than again you define answer variable inside { }

再一次在 { } 中定义 answer 变量

String answer = answer2 + " "; // duplicate

---

---

you should use if for the condition and terminate the ; from while like

您应该使用 if 作为条件并终止 ; 从喜欢

while(condition){
 }

and use

并使用

 answer = answer2 + " ";

instead of

代替

 String answer = answer2 + " ";