需要帮助来了解有关 While 循环条件语句和类型转换的一些基本 Java 概念

Question

我只是想编写一个简单的计算器，它工作正常......我现在要做的是包含一个“do while”或“while”循环来重复一个语句，直到用户输入四个基本操作符之一。我已经使用其他方法（if 和 switch）实现了它，但我想简化它。此外，我在学习如何解析字符scanner和JPane方法时遇到了很多问题。我可以使用互联网上的各种资源来实现，但是一个简单的方法可以帮助我更清楚地理解逻辑，而不仅仅是实现将受到高度赞赏......    public class MyCalculator{    public static void main (String [] args){    // Let us code a simple calculator    char OP;    System.out.println("This is a simple calculator that will do basic calculations such as :\nAddition, Multiplication, Substraction and Division.");    // Create a scanner object to Read user Input.    Scanner input = new Scanner(System.in);    System.out.println("Enter Any positive number followed by pressing ENTER.");    int firstNum = input.nextInt();    // Need to Loop the below statement till one of the four (+,-,*,/) operator is entered.    System.out.println("Enter your choice of OPERATOR sign followed by pressing ENTER.");    OP = input.next().charAt(0);    System.out.println("Enter your Second number followed by an ENTER stroke.");    int secNum = input.nextInt();    // Various possible Resolution    int RSum = firstNum+secNum;    int RSubs= firstNum-secNum;    int RPro = firstNum*secNum;    double DPro = firstNum/secNum;    // Conditional statements for Processing    Switch (OP){     case '+': System.out.println("The Resulting sum is "+ RSum);    break;    case '-': System.out.println("The Resulting sum is "+ RSubs);    break;    case '*': System.out.println("The Resulting Product is "+ RPro);    break;    case '/': System.out.println("The Resulting Divisional product is "+ DPro);    break;    default : System.out.println("Try Again");        }    }}

Answer 1

你可以使用这样的东西：

while(scanner.hasNext()) {

  //some code

   int number = scanner.NextInt();

}

但我会实现一个计算器如下：

int num1 = scanner.NextInt();

String op = scanner.Next();

int num2 = scanner.NextInt();

您可以按如下方式遍历字符串并进行检查：

for (char ch : exampleString.toCharArray()){

  System.out.println(ch);

}

您还可以按如下方式循环字符串：

for (int i=0; i<examplestring.length(); i++) {

  char c = examplestring.charAt(i);

}

您可以循环直到获得 + 或 - ，如下所示：

char operator;    

do {

  char operator = scanner.next().get(0);

}while(operator != '+' || operator != '-')

您可以循环和打印错误消息，如下所示：

char operator;

do {

  char operator = scanner.next().get(0);

  if(!isValidOperator(operator)) {

    System.out.println("invalid operator");

  }

}while(!isValidOperator(operator))

public boolean isValidOperator(char operator) {

  if(operator == '+') {

    return true;

  } else if (operator == '-') {

    return true;

  }

  return false;

}