java - 错误 : incompatible types: char cannot be converted to String

Question

我做错了什么。我的运算符 operation 已经是一个字符串。

javac Arithmetic2.java

Arithmetic2.java:44: error: incompatible types: char cannot be converted to String
                        case '+' : { result = add; }
                             ^
Arithmetic2.java:45: error: incompatible types: char cannot be converted to String
                        case '-' : { result = sub; }
                             ^
Arithmetic2.java:46: error: incompatible types: char cannot be converted to String
                        case '*' : { result = mul; }
                             ^
Arithmetic2.java:47: error: incompatible types: char cannot be converted to String
                        case '/' : { result = div; }
                             ^
Arithmetic2.java:48: error: incompatible types: char cannot be converted to String
                        case '%' : { result = per; }
                             ^
5 errors

算术2.java

// Arithmetic2.java - This program performs arithmetic, ( +. -, *. /, % )     on two numbers
// Input:  Interactive.
// Output:  Result of arithmetic operation

import javax.swing.*;

public class Arithmetic2
{
public static void main(String args[])
{
    double numberOne, numberTwo;
    String numberOneString, numberTwoString;
    String operation;
    double result;

    numberOneString = JOptionPane.showInputDialog("Enter the first number: ");
    numberOne = Double.parseDouble(numberOneString);
    numberTwoString = JOptionPane.showInputDialog("Enter the second number: ");
    numberTwo = Double.parseDouble(numberTwoString);
    operation = JOptionPane.showInputDialog("Enter an operator (+.-.*,/,%): ");

    // Call performOperation method here
    performOperation(numberOne, numberTwo, operation, result);

    System.out.format("%.2f",numberOne);
    System.out.print(" " + operation + " ");
    System.out.format("%.2f", numberTwo);
    System.out.print(" = ");
    System.out.format("%.2f", result);

    System.exit(0);

} // End of main() method.

// Write performOperation method here.
public static double performOperation(double numberOne, double numberTwo, String operation, double result) {
    double add = numberOne+numberTwo;
    double sub = numberOne-numberTwo;
    double mul = numberOne*numberTwo;
    double div = numberOne/numberTwo;
    double per = numberOne%numberTwo;

    switch(operation) {
        case '+' : { result = add; }
        case '-' : { result = sub; }
        case '*' : { result = mul; }
        case '/' : { result = div; }
        case '%' : { result = per; }
        default : { System.out.println("Invalid operator!"); }
    }
}
} // End of Arithmetic2 class.

Answer 1

自 JOptionPane::showInputDialog在大多数情况下返回 String(除了 one 需要大量参数来帮助它返回正确的对象类型)，最好在后续流程中使用 String .

只需将 switch 案例引号从 '' (char) 更改为 "" (String)。您无需更改方法参数。

switch(operation) {
    case "+" : { result = add; break; }
    case "-" : { result = sub; break; }
    case "*" : { result = mul; break; }
    case "/" : { result = div; break; }
    case "%" : { result = per; break; }
    default : { System.out.println("Invalid operator!"); break; }
}

编辑:不要忘记 breaks。