我最近发布了一个有关扫描仪未给出预期结果的问题,并了解到我的问题是我没有使用 .nextLine()
刷新扫描仪。我对我正在开发的程序感到困惑,因为我正在正确地刷新扫描仪,但是当我测试我的程序时,如果 - 当提示输入数字时 - 我输入一个字符串,我会得到错误的输出。它重复相同的循环两次。
循环的顶部调用了 nextLine(),处理无效输入(例如我正在输入的字符串)的 else block 也调用了 nextLine()。但不知怎的,我的输出仍然很差
具体来说,这是一个错误输出的示例,用户输入为粗体,有问题的输出为斜体
输入左侧值:2
输入运算符:-
输入右侧值:t
输入无效
输入运算符(+ - * 或/:
无效运算符
输入运算符(+ - * 或/:
上面四行会自动输出到控制台。
这是代码片段,在错误代码所在的地方有一个大注释。我本想只发布问题所在的 while block ,但由于 while block 是程序的大部分,并且整个程序只比该部分大一点,所以我认为最好发布全部内容。
import java.util.Scanner;
import javax.swing.JOptionPane;
public class Calculator{
public static void main(String[] args){
double leftHandVal = 0.0;
//Output Title & Instructions
System.out.print("!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!\n");
System.out.print("!\t\t\t\t!\n");
System.out.print( "!\t INSTRUCTIONS\t\t!\n");
System.out.print("!\t\t\t\t!\n");
System.out.print("! INPUT\t\tOUTPUT\t\t!\n");
System.out.print("! *******\t *********\t\t!\n");
System.out.print("! c or C\t\tClear\t\t!\n");
System.out.print("! q or Q\t\tQuit\t\t!\n");
System.out.print("! +\t\tAddition\t\t!\n");
System.out.print("! -\t\tSubtraction\t!\n");
System.out.print("! *\t\tMultiplication\t!\n");
System.out.print("! /\t\tDivision\t\t!\n");
System.out.print("!\t\t\t\t!\n");
System.out.print("!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!\n\n");
while(true){
Scanner input = new Scanner(System.in);
char op = '\n';//(+, -, *, or /) will use in switch statement for their ascii decimal values
System.out.print("Enter the left-hand value: ");
//these blocks allow the code at the very bottom to not erroneously ask the user for extra input with hasNext() calls
if(input.hasNext("c") || input.hasNext("C")){//even though its unlikely for a user to clear so early...just in case
leftHandVal = 0.0;
}
else if(input.hasNext("q") || input.hasNext("Q")){//even though its unlikely for a user to quit so early...just in case
op = 113;//assign q for quit code
}
else if(input.hasNextDouble()){
leftHandVal = input.nextDouble();
/*
*
*BAD CODE INSIDE WHILE BELOW
*BAD CODE INSIDE WHILE BELOW
*BAD CODE INSIDE WHILE BELOW
*BAD CODE INSIDE WHILE BELOW
*
*/
while(true){
input.nextLine();
double rightHandVal = 0.0;
System.out.print("\nEnter operator (+ - * or / : ");
if(input.hasNext()){
op = input.next().charAt(0);
}
//if user wishes to cancel or quit on operator prompt, break out of inner while to access the clear and quit code
if(op == 99 || op == 67){
op = 99;
break;
}
else if(op == 113 || op == 81){
op = 113;
break;
}
else if((op != 43) && (op != 45) && (op != 42) && (op != 47)){//if invalid operator, restart inner while
System.out.print("Invalid Operator");
continue;
}
System.out.print("Enter the right-hand value: ");
if(input.hasNextDouble()){
rightHandVal = input.nextDouble();
switch(op){
case 43:
System.out.printf("%.3f + %.3f = %.3f", leftHandVal, rightHandVal, (leftHandVal + rightHandVal));
leftHandVal += rightHandVal;
break;
case 45:
System.out.printf("%.3f - %.3f = %.3f", leftHandVal, rightHandVal, (leftHandVal - rightHandVal));
leftHandVal -= rightHandVal;
break;
case 42:
System.out.printf("%.3f * %.3f = %.3f", leftHandVal, rightHandVal, (leftHandVal * rightHandVal));
leftHandVal *= rightHandVal;
break;
case 47:
System.out.printf("%.3f / %.3f = %.3f", leftHandVal, rightHandVal, (leftHandVal / rightHandVal));
leftHandVal /= rightHandVal;
break;
}
}
//if clear or quit requested from prompt for right-hand value, break to reach the clear and quit code
else if(input.hasNext("c") || input.hasNext("C")){
op = 99;
break;
}
else if(input.hasNext("q") || input.hasNext("Q")){
op = 113;
break;
}
else{
System.out.print("Invalid Input");
}
}
}
//if c || C reset op to null and restart outer while
if(op == 99 || op == 67){
op = '\n';
leftHandVal = 0.0;
continue;
}
//else if q || Q, prompt user with a popup to confirm.
if(op == 113 || op == 81){
int response = JOptionPane.showConfirmDialog(null, "QUIT CALCULATOR?", null, JOptionPane.YES_NO_OPTION);
if(response == 0){
System.exit(0);
}
continue;
}
}
}
}
最佳答案
else if(input.hasNext("c") || input.hasNext("C"))
{
op = 99;
break;
}
else if(input.hasNext("q") || input.hasNext("Q")){
op = 113;
break;
}
else{
System.out.print("Invalid Input");
}
在此代码中,当您输入“t”作为右手值时,您只需检查 hasNext();
最后它会出现 else 并打印 Invalid Input。
但是输入仍然具有值“t”,因此它会再次开始第二个while循环,并且
System.out.print("\nEnter operator (+ - * or / : ");
if(input.hasNext()){
op = input.next().charAt(0);
}
检查已经有“t”的input.hasNext(),因此采用“t”并继续。
解决方案是在进入 while 循环之前刷新“t”。
关于Java:扫描仪输出错误,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/19500001/