[英]Why does my first print statement print twice when the loop restarts?
當我輸入第一個或第二個數字值的無效輸入時"Enter an operation (+, -, *, /, quit)"
為什么"Enter an operation (+, -, *, /, quit)"
打印兩次? "Enter an operation (+, -, *, /, quit)"
無效后"Enter an operation (+, -, *, /, quit)"
循環應重新啟動並打印"Enter an operation (+, -, *, /, quit)"
。
public static void main(String[] args) {
Scanner scnr = new Scanner(System.in);
int i = 1;
while(i > 0){
String operation = "";
int firstInt = 0;
int secondInt = 0;
double firstDouble = 0.0;
double secondDouble = 0.0;
int intAnswer = 0;
double answer = 0.0;
boolean first = false;
boolean second = false;
System.out.println("Enter an operation (+, -, *, /, quit)");
operation = scnr.next();
if(operation.equals("+")|| operation.equals("-") || operation.equals("*") || operation.equals("/")){
System.out.println("Enter first numeric value");
if(scnr.hasNextInt()){
firstInt = scnr.nextInt();
first = true;
}else if(scnr.hasNextDouble()){
firstDouble = scnr.nextDouble();
}
else{
continue;
}
System.out.println("Enter second numeric value");
if(scnr.hasNextInt()){
secondInt = scnr.nextInt();
second = true;
}else if(scnr.hasNextDouble()){
secondDouble = scnr.nextDouble();
}
else{
continue;
}
}
else if(operation.equals("quit")){
System.exit(0);
scnr.close();
break;
}
}
}
使用Scanner.nextInt()
等會使掃描器緩沖區保持打開狀態,因為它不會占用整行,而是僅將最接近的原始值和該行的其余部分存儲在掃描器緩沖區中,並且僅由新的行調用使用。 這會導致很多意外情況,並且難以解決錯誤。
使用掃描儀獲取原始數據類型時的更好做法是使用
double yourDouble = Double.parseDouble(Scanner.nextLine());
//for int you use Integer.parserInt(Scanner.nextLine()
這樣一來,掃描程序就消耗了整行,並且緩沖區中沒有存儲任何內容,而且您不會因輸出/輸入流出現異常而感到頭疼。
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