如何允许用户使用java在Array中输入结果？

Question

我想让用户输入一些竞赛结果(至少2人，最多7人)，我觉得我可以使用更短的代码，(我是Java的初学者，只有2个月，所以任何建议都是非常有用的！)谢谢，守则如下：

int entrants = 0;
String[][] runners = new String[2][2];
boolean valid = false; //this is for the initial number of runners question - it will stay false and keep us in the loop until a number between 2-7 is entered
System.out.println("Please enter the number of runners for this race (2 to 7 entrants permitted)");
entrants = input.nextInt();
input.nextLine();

while(valid == false){

    if(entrants < 2) {
        System.out.println("You need at least 2 runners for a race, please re-enter the number of runners");
        entrants = input.nextInt();
        input.nextLine();
    } else if (entrants > 7) {
        System.out.println("You have entered too many runners for this race (max runners is 7). Please re-enter the number of runners");
        entrants = input.nextInt();
        input.nextLine();
    } else {
        System.out.printf("You have entered %d runners\n", entrants);
        runners = new String[entrants][2];
        valid = true;
    }
}

Answer 1

让我们完全重构代码。

我对代码做了一个单一的功能更改:我反复问最初的问题，而不是要求重新输入。这样就更简单了。

// --- only *declare* entrants, don't assign it an initial value that you don't want
int entrants;
// --- get rid of that pesky warning you get if you don't close `Scanner` instances
try (Scanner input = new Scanner(System.in)) {
    // --- we'll just use a break statement to make the while loop a lot easier
    while(true) {
        //  --- this is the question that gets (re-) asked
        System.out.println("Please enter the number of runners for this race (2 to 7 entrants permitted)");

        // --- only now we assign a possible value
        // --- note that you normally first test for presence using hasNextInt!
        entrants = input.nextInt();
        input.nextLine();

        // --- nothing wrong with the original if statement
        if (entrants < 2) {
            System.out.println("You need at least 2 runners for a race.");
        } else if (entrants > 7) {
            System.out.println("You have entered too many runners for this race (max runners is 7).");
        } else {
            // --- use a clear comment *why* you break, this is an exit point for the loop after all
            // we've found a correct number of entrants
            break;
        }
    }
}
System.out.printf("You have entered %d runners\n", entrants);
// --- there was absolutely no reason to define or initialize the array before...
String[][] runners = new String[entrants][2];

当然，要使代码实际上更小，请删除以---开头的注释。

Answer 2

你有很多行可以做同样的事情，只要稍作调整就可以合并：

int entrants = 0;
String[][] runners = null; //no need to create an array that you'll be throwing away
boolean valid = false; //this is for the initial number of runners question - it will stay false and keep us in the loop until a number between 2-7 is entered
System.out.println("Please enter the number of runners for this race (2 to 7 entrants permitted)");

do {
  //read the input
  entrants = input.nextInt();
  input.nextLine();

  //validate (we'll keep your messages)
  if(entrants < 2) {
    System.out.println("You need at least 2 runners for a race, please re-enter the number of runners");      
  } else if (entrants > 7) {
    System.out.println("You have entered too many runners for this race (max runners is 7). Please re-enter the number of runners");    
  } else {
    System.out.printf("You have entered %d runners\n", entrants);

    //create the array and set the exit condition
    runners = new String[entrants][2];
    valid = true;
  }
} while (!valid);

注意do-while的使用，它类似于while-循环，但在迭代后评估条件，即循环体至少运行一次。

进一步的改进可以包括将约束放入常量(即min =2和max = 7)，而不是将它们放在所有代码中。