当我学习Java时，我正在尝试在Java上创建一个简单的计算器程序作为一个简单的第一个项目。
问题：在我运行程序并完成计算后，我想让用户选择是否要结束程序或进行更多计算。由于某种原因，程序没有使用我放在其中的（if）语句，它似乎跳过它并结束我的程序而不允许用户在最后输入他的选择。
如果我的问题不明确，我真的很抱歉，我在网上找不到解决问题的方法，如果我的代码看起来很乱，我会道歉。
import java.util.Scanner;
public class Calculator {
public static void main(String[] args) {
Scanner input = new Scanner(System.in);
double fnum, snum, answer;
String choice, name, in;
System.out.println("Hello, whats your name?");
name = input.nextLine();
System.out.println("");
System.out.println("Oh so your name is " + name + "!");
System.out.println("");
System.out.println("This program is a calculator that will do simple calculation of two numbers");
System.out.println("There are four different options to choose from:");
boolean running = true;
CAL:
while (running) {
System.out.println("type a for Addition, b for subtraction, c for multiplication and d for division");
System.out.println("Then press enter!");
choice = input.nextLine();
while (!choice.equals("a") &&
!choice.equals("A") &&
!choice.equals("b") &&
!choice.equals("B") &&
!choice.equals("c") &&
!choice.equals("C") &&
!choice.equals("d") &&
!choice.equals("D")) {
System.out.println("Wrong choice, Please try again");
System.out.println("type a for Addition, b for subtraction, c for multiplication and d for division");
choice = input.nextLine();
}
if (choice.equals("a") || choice.equals("A")) {
System.out.println(name +" You have chosen Addition");
System.out.println("Type the first number:");
fnum = input.nextDouble();
System.out.println("Type the second number:");
snum = input.nextDouble();
System.out.println("your answer is:");
Addition addy = new Addition(fnum,snum);
System.out.println(addy.getans());
}
if (choice.equals("b") || choice.equals("B")) {
System.out.println(name +" You have chosen Subtraction");
System.out.println("Type the first number:");
fnum = input.nextDouble();
System.out.println("Type the second number:");
snum = input.nextDouble();
answer = fnum - snum;
System.out.println("your answer is:"
+ answer);
}
if (choice.equals("c") || choice.equals("C")) {
System.out.println(name +" You have chosen Multiplication");
System.out.println("Type the first number:");
fnum = input.nextDouble();
System.out.println("Type the second number:");
snum = input.nextDouble();
answer = fnum * snum;
System.out.println("your answer is:"
+ answer);
}
if (choice.equals("d") || choice.equals("D")) {
System.out.println(name +" You have chosen Addition");
System.out.println("Type the first number:");
fnum = input.nextDouble();
while (fnum == 0) {
System.out.println("invalid try again!");
fnum = input.nextDouble();
}
System.out.println("Type the second number:");
snum = input.nextDouble();
answer = fnum / snum;
System.out.println("your answer is:"
+ answer);
}
System.out.println("");
System.out.println("Thank you " + name + " for using this simple calculator :)");
System.out.println("If you would like to try again press a the press Enter, if you wish to exit press any botton and then press enter");
in = input.nextLine();
if (in.equals("a")) {
System.out.println("");
System.out.println("Thank you, please choose again");
System.out.println("");
} else {
System.out.println("Thank you and goodbye");
break;
}
}
}
}
答案 0 :(得分：0)
这是由nextInt / Double / etc行为引起的一个简单问题。
这些方法不会读取以下换行符，因此下一个nextLine将始终返回一个空字符串（当前行的其余部分）。
尝试使用Double.parseDouble(input.nextLine());
if (choice.equals("a") || choice.equals("A")) {
System.out.println(name + " You have chosen Addition");
System.out.println("Type the first number:");
fnum = Double.parseDouble(input.nextLine());
System.out.println("Type the second number:");
snum = Double.parseDouble(input.nextLine());
System.out.println("your answer is:");
Addition addy = new Addition(fnum, snum);
System.out.println(addy.getans());
}
您可以注意到，调用最后in = input.nextLine();调用以询问用户输入将始终为空字符串。