使用if else语句输入Java Scanner [英] Java Scanner input with if else statement

问题描述

您好我是java的新手并且正在尝试进行测验。我想提出一个问题，用户必须将单词中的单词组合成对。像A1 B4 C3 D2一样。我现在做的是使用if else语句来检查输入是否是正确的答案，但它只适用于1A。对于其他人，我可以做6个输入，这不是我想要的，即使有正确的输入，我也没有意见。

Hi I'm new to java and trying to make a Quiz to practice. I wanna make a Question where the user has to combine words from to categories to pairs. Like A1 B4 C3 D2. What I did now is using an if else statement to check if the input is the correct answer, but it only works with 1A. For the others I can do 6 inputs, which is not what I want, and even if there's a correct one I don't get a point.

public class HelloWorld {

    public static void main(String[] args) {

        Scanner walther = new Scanner(System.in);

        String cro = "1A";
        String dan = "2C";
        String fin = "4D";
        String dut = "3F";
        String fre = "5B";
        String ger = "6E";
        int x = 0;


        if (cro.equalsIgnoreCase(walther.nextLine())){
            ++x;
            walther.close();
        }
        else if (dan.equalsIgnoreCase(walther.nextLine())){
            ++x;
            walther.close();
        }
        else if (fin.equalsIgnoreCase(walther.nextLine())){
            ++x;
            walther.close();
        }
        else if (dut.equalsIgnoreCase(walther.nextLine())){
            ++x;
            walther.close();
        }
        else if (fre.equalsIgnoreCase(walther.nextLine())){
            ++x;
            walther.close();
        }
        else if (ger.equalsIgnoreCase(walther.nextLine())){
            ++x;
            walther.close();
        }
        else {
            walther.close();
        }

    System.out.println(x + " Point!");
    }
}

推荐答案

致电 nextLine（）从扫描仪中消耗一行。你在第一个 if 上执行此操作，因此后续的 else if 分支实际上是在比较以下行（或 null ，如果您没有任何其他输入）。相反，您应该只使用该行一次，将其保存到本地变量并在比较中使用它：

Calling nextLine() consumes a line from the scanner. You do this on the first if, so the subsequent else if branches are, in fact, comparing the following lines (or null, if you don't have any additional input). Instead, you should consume the line only once, save it to a local variable and use that in your comparisons:

String input = walther.nextLine();
if (cro.equlasIgnoreCase(input)) { // etc...

拥有说，使用和if-else结构不是最好的解决方案。使用可以节省大量代码膨胀不区分大小写 TreeSet ：

Having said that, using and if-else structure isn't the neatest solution. You can save a lot of code bloat by using a case insensitive TreeSet:

TreeSet<String> set = new TreeSet<>(String.CASE_INSENSITIVE_ORDER);
set.addAll(Arrays.asList("1A", "2C", "4D", "3F", "5B", "6E"));
String input = walther.nextLine();
if (set.contains(input)) {
   ++x;
   walther.close();
}

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