Java 错误：不兼容的类型：无法将字符转换为字符串

我做错了什么。我的名为operation的运算符已经是字符串

javac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.

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.

---

您需要将单引号替换为双引号，因为Java将单引号解释为字符，因此您的代码需要读取：

switch(operation) {
    case "+" : {result = add; }  // and so on...

}

---

希望这有点帮助：-）

将

操作

变量转换为

字符

类型，它就可以工作了

---

或者通过将单引号替换为双引号将开关选项更改为字符串，因为它会将选项更改为

String

是的，

操作

是字符串，但错误告诉您

'+'

不是字符串

在Java中，双引号用于生成字符串文字，单引号用于生成字符文字。您正在尝试将字符串与字符进行比较

如果将

“+”

（以及

大小写的其余操作数）更改为
“+”
，它应该可以工作。
因为在大多数情况下返回
字符串
（除了需要大量参数来帮助它返回正确的对象类型），最好在后续流中使用
字符串

只需将
开关
cases引号从
'
（char）更改为
'
（String）。您不需要更改方法参数

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
break
s.
操作
是一个
字符串
，但是您的
case
语句都使用
字符
常量。选项1：更改
开关
，如

switch(operation.charAt(0))

选项2：更改
case
语句，如

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

但是，在这两种情况下，
{}
都没有意义，
case
语句将通过-添加中断

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;
}

正如上面所说的：您正试图将
字符串
（
操作
）与
字符
（切换案例）进行比较。将
字符
更改为
字符串
，反之亦然。是的，这非常有意义。我不知道我是怎么错过的。谢谢