提问人：G-Arthur 提问时间：3/19/2021 更新时间：3/20/2021 访问量：75
JAVA 扫描程序在使用 bag 时导致 if 语句问题
JAVA scanner causes if statement problems when using bag
问：
我是 JAVA 的新手，一直在使用 IDE，每当我尝试检查 bag 是否包含与给定输入相同的字符串时，JAVA 都会将其计为 FALSE，即使 if 语句（例如“is input equal to 1”和“is 1 inside the bag”）传递为 true。这是我的代码摘录，我将不胜感激任何帮助和建议。
//user input
System.out.println("Please enter a string (to exit, enter 'exit'): ");
a=sc.next();
if (a.equals("1")) {System.out.println("adpkgnosıfbgojadnofabsndofgna");}
if (ValidAnswers1.contains("1")) {System.out.println("adpkgnosıfbgojadnofabsndofgna");}
//error detection. after I learn bag it will become if bag contains string s.
if (ValidAnswers1.contains(a)) {correct_input=1;} else {correct_input=0;}
while (correct_input==0)
{
System.out.println("you entered:"+ a+".");
System.out.println("Please enter a valid string (to exit, enter 'exit')");
a = sc.next();
if (ValidAnswers1.contains(a)) {correct_input=1;} else {correct_input=0;}
}
控制台打印出两个 keymashes，然后转移到 while 循环中。我已经通过使用固定变量进行测试来检查以确保 while 循环正确，但是当使用扫描仪时，它似乎有错误。
答：
0赞
Dam
3/19/2021
#1
我不明白，你真正想要的是什么，我做了测试，但工作正常。看看类，也许是变量中的一些错误或其他东西
public class Main {
public static void main(String[] args){
Scanner sc = new Scanner(System.in);
String a;
String ValidAnswers1 = "1";
int correct_input = 0;
//user input
System.out.println("Please enter a string (to exit, enter 'exit'): ");
a = sc.next();
if (a.equals("1")) {
System.out.println("adpkgnosıfbgojadnofabsndofgna");
}
if (ValidAnswers1.contains("1")) {
System.out.println("adpkgnosıfbgojadnofabsndofgna");
}
//error detection. after I learn bag it will become if bag contains string s.
if (ValidAnswers1.contains(a)) {
correct_input=1;
} else {
correct_input=0;
}
while (correct_input==0) {
System.out.println("you entered:"+ a+".");
System.out.println("Please enter a valid string (to exit, enter 'exit')");
a = sc.next();
if (ValidAnswers1.contains(a)) {
correct_input=1;
} else {
correct_input=0;
}
}
}
输出如下：
Please enter a string (to exit, enter 'exit'):
a
adpkgnos?fbgojadnofabsndofgna
you entered:a.
Please enter a valid string (to exit, enter 'exit')
1
------------------------------------------------------------------------
BUILD SUCCESS
------------------------------------------------------------------------
评论
0赞
G-Arthur
3/19/2021
你能用袋子试试吗？在我的代码中，ValidAnswers1 是一个袋子，我认为这是问题的原因。或者把它做成一个像“1 2 3 4 exit”这样的字符串，然后使用 .contains（） 会更好吗？
0赞
Dam
3/20/2021
我不知道“bag”这个词，但我相信创建一个更容易的字符串数组会更容易。
0赞
Dam
3/20/2021
我来举个例子
0赞
Dam
3/20/2021
我完成了这个例子，试着理解我做了什么，如果你不明白再问一次，我将“correct_input”的值改为布尔值，因为我认为会更有条理和安全，此外这是一个很好的做法，因为代码只处理两个数字。
0赞
Dam
3/20/2021
#2
//Create a new Object Scan in the memmory
Scanner scan = new Scanner(System.in);
String input;
String[] validAnswers = new String[]{"1","2","3","exit"};
boolean isCorrect = false;
//The method equalsIgnoreCase means that the text can be in uppercase too;
/*The number between the tags "[]" means the number in the array since arrays
starts with number "0" */
do{
System.out.println("Please enter a string (to exit, enter 'exit'): ");
input = scan.next();
if(input.equalsIgnoreCase(validAnswers[0])){
isCorrect = true;
System.out.println("Number 1");
}else if(input.equalsIgnoreCase(validAnswers[1])){
isCorrect = true;
System.out.println("Number 2");
}else if(input.equalsIgnoreCase(validAnswers[2])){
isCorrect = true;
System.out.println("Number 3");
}else if(input.equalsIgnoreCase(validAnswers[3])){
isCorrect = true;
System.out.println("EXIT!");
//You could use the method System.exit(0) to finish the program;
//If you put "1" in the exit value means that the prgram finished with some error;
//System.exit(0);
}else{
//If the Answers is different from all of the others;
System.out.println("you entered: " + input +".");
System.out.println("Please enter a valid string (to exit, enter 'exit')");
}
}while(isCorrect != true);
//I used the method do{}while because it's the only method that will exacute at least once;
}
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