使用开关的Java 4操作员计算器不工作

当我运行它时，什么也没发生。让我感到奇怪的是，系统如何输出你想做的事也不起作用。顺便说一句，扫描器是在它前面调用的。如果我做错了什么，请告诉我：）任何帮助都是巨大的

Scanner scanner3 = new Scanner(System.in);
String operator = scanner3.nextLine();

System.out.println("What do you want to do? (add, subtract, multiply, or divide?)");

switch (operator){

case "add": System.out.println("Enter number one ");
    Scanner scanner4 = new Scanner(System.in);
    double addnum1 = scanner4.nextDouble();
    System.out.println("Enter number two ");
    Scanner scanner5 = new Scanner(System.in);
    double addnum2 = scanner5.nextDouble();
    System.out.print("the answer is: ");
    System.out.println( addnum1 + addnum2);
    break;

case "subtract": System.out.println("Enter number one");
    Scanner scanner7 = new Scanner(System.in);
    double subnum1 = scanner7.nextDouble();
    System.out.println("Enter number two ");
    Scanner scanner8 = new Scanner(System.in);
    double subnum2 = scanner8.nextDouble();
    System.out.print("the answer is: ");
    System.out.println( subnum1 - subnum2 );
    break;

case "multiply": System.out.println("Enter number one");
    Scanner scanner9 = new Scanner(System.in);
    double mulnum1 = scanner9.nextDouble();
    System.out.println("Enter number two ");
    Scanner scanner10 = new Scanner(System.in);
    double mulnum2 = scanner10.nextDouble();
    System.out.print("the answer is: ");
    System.out.println( mulnum1 * mulnum2 );
    break;
case "divide": System.out.println("Enter number one");
    Scanner scanner11 = new Scanner(System.in);
    double divnum1 = scanner11.nextDouble();
    System.out.println("Enter number two ");
    Scanner scanner12 = new Scanner(System.in);
    double divnum2 = scanner12.nextDouble();
    System.out.print("the answer is: ");
    System.out.println( divnum1 / divnum2 );
    break;
}

第一次印刷

Scanner scanner3 = new Scanner(System.in);
String operator = scanner3.nextLine();

System.out.println("What do you want to do? (add, subtract, multiply, or divide?)");

switch (operator){

case "add": System.out.println("Enter number one ");
    Scanner scanner4 = new Scanner(System.in);
    double addnum1 = scanner4.nextDouble();
    System.out.println("Enter number two ");
    Scanner scanner5 = new Scanner(System.in);
    double addnum2 = scanner5.nextDouble();
    System.out.print("the answer is: ");
    System.out.println( addnum1 + addnum2);
    break;

case "subtract": System.out.println("Enter number one");
    Scanner scanner7 = new Scanner(System.in);
    double subnum1 = scanner7.nextDouble();
    System.out.println("Enter number two ");
    Scanner scanner8 = new Scanner(System.in);
    double subnum2 = scanner8.nextDouble();
    System.out.print("the answer is: ");
    System.out.println( subnum1 - subnum2 );
    break;

case "multiply": System.out.println("Enter number one");
    Scanner scanner9 = new Scanner(System.in);
    double mulnum1 = scanner9.nextDouble();
    System.out.println("Enter number two ");
    Scanner scanner10 = new Scanner(System.in);
    double mulnum2 = scanner10.nextDouble();
    System.out.print("the answer is: ");
    System.out.println( mulnum1 * mulnum2 );
    break;
case "divide": System.out.println("Enter number one");
    Scanner scanner11 = new Scanner(System.in);
    double divnum1 = scanner11.nextDouble();
    System.out.println("Enter number two ");
    Scanner scanner12 = new Scanner(System.in);
    double divnum2 = scanner12.nextDouble();
    System.out.print("the answer is: ");
    System.out.println( divnum1 / divnum2 );
    break;
}

System.out.println("What do you want to do? (add, subtract, multiply or divide?)");

是在

Scanner scanner3 = new Scanner(System.in);
String operator = scanner3.nextLine();

System.out.println("What do you want to do? (add, subtract, multiply, or divide?)");

switch (operator){

case "add": System.out.println("Enter number one ");
    Scanner scanner4 = new Scanner(System.in);
    double addnum1 = scanner4.nextDouble();
    System.out.println("Enter number two ");
    Scanner scanner5 = new Scanner(System.in);
    double addnum2 = scanner5.nextDouble();
    System.out.print("the answer is: ");
    System.out.println( addnum1 + addnum2);
    break;

case "subtract": System.out.println("Enter number one");
    Scanner scanner7 = new Scanner(System.in);
    double subnum1 = scanner7.nextDouble();
    System.out.println("Enter number two ");
    Scanner scanner8 = new Scanner(System.in);
    double subnum2 = scanner8.nextDouble();
    System.out.print("the answer is: ");
    System.out.println( subnum1 - subnum2 );
    break;

case "multiply": System.out.println("Enter number one");
    Scanner scanner9 = new Scanner(System.in);
    double mulnum1 = scanner9.nextDouble();
    System.out.println("Enter number two ");
    Scanner scanner10 = new Scanner(System.in);
    double mulnum2 = scanner10.nextDouble();
    System.out.print("the answer is: ");
    System.out.println( mulnum1 * mulnum2 );
    break;
case "divide": System.out.println("Enter number one");
    Scanner scanner11 = new Scanner(System.in);
    double divnum1 = scanner11.nextDouble();
    System.out.println("Enter number two ");
    Scanner scanner12 = new Scanner(System.in);
    double divnum2 = scanner12.nextDouble();
    System.out.print("the answer is: ");
    System.out.println( divnum1 / divnum2 );
    break;
}

.nextLine()

因此，您的程序在打印第一条消息之前需要输入

Scanner scanner3 = new Scanner(System.in);
String operator = scanner3.nextLine();

System.out.println("What do you want to do? (add, subtract, multiply, or divide?)");

switch (operator){

case "add": System.out.println("Enter number one ");
    Scanner scanner4 = new Scanner(System.in);
    double addnum1 = scanner4.nextDouble();
    System.out.println("Enter number two ");
    Scanner scanner5 = new Scanner(System.in);
    double addnum2 = scanner5.nextDouble();
    System.out.print("the answer is: ");
    System.out.println( addnum1 + addnum2);
    break;

case "subtract": System.out.println("Enter number one");
    Scanner scanner7 = new Scanner(System.in);
    double subnum1 = scanner7.nextDouble();
    System.out.println("Enter number two ");
    Scanner scanner8 = new Scanner(System.in);
    double subnum2 = scanner8.nextDouble();
    System.out.print("the answer is: ");
    System.out.println( subnum1 - subnum2 );
    break;

case "multiply": System.out.println("Enter number one");
    Scanner scanner9 = new Scanner(System.in);
    double mulnum1 = scanner9.nextDouble();
    System.out.println("Enter number two ");
    Scanner scanner10 = new Scanner(System.in);
    double mulnum2 = scanner10.nextDouble();
    System.out.print("the answer is: ");
    System.out.println( mulnum1 * mulnum2 );
    break;
case "divide": System.out.println("Enter number one");
    Scanner scanner11 = new Scanner(System.in);
    double divnum1 = scanner11.nextDouble();
    System.out.println("Enter number two ");
    Scanner scanner12 = new Scanner(System.in);
    double divnum2 = scanner12.nextDouble();
    System.out.print("the answer is: ");
    System.out.println( divnum1 / divnum2 );
    break;
}

您可以在所有情况下使用相同的扫描仪，更好、更干净的代码

Scanner scanner3 = new Scanner(System.in);
String operator = scanner3.nextLine();

System.out.println("What do you want to do? (add, subtract, multiply, or divide?)");

switch (operator){

case "add": System.out.println("Enter number one ");
    Scanner scanner4 = new Scanner(System.in);
    double addnum1 = scanner4.nextDouble();
    System.out.println("Enter number two ");
    Scanner scanner5 = new Scanner(System.in);
    double addnum2 = scanner5.nextDouble();
    System.out.print("the answer is: ");
    System.out.println( addnum1 + addnum2);
    break;

case "subtract": System.out.println("Enter number one");
    Scanner scanner7 = new Scanner(System.in);
    double subnum1 = scanner7.nextDouble();
    System.out.println("Enter number two ");
    Scanner scanner8 = new Scanner(System.in);
    double subnum2 = scanner8.nextDouble();
    System.out.print("the answer is: ");
    System.out.println( subnum1 - subnum2 );
    break;

case "multiply": System.out.println("Enter number one");
    Scanner scanner9 = new Scanner(System.in);
    double mulnum1 = scanner9.nextDouble();
    System.out.println("Enter number two ");
    Scanner scanner10 = new Scanner(System.in);
    double mulnum2 = scanner10.nextDouble();
    System.out.print("the answer is: ");
    System.out.println( mulnum1 * mulnum2 );
    break;
case "divide": System.out.println("Enter number one");
    Scanner scanner11 = new Scanner(System.in);
    double divnum1 = scanner11.nextDouble();
    System.out.println("Enter number two ");
    Scanner scanner12 = new Scanner(System.in);
    double divnum2 = scanner12.nextDouble();
    System.out.print("the answer is: ");
    System.out.println( divnum1 / divnum2 );
    break;
}

Scanner scanner_all = new Scanner(System.in);
System.out.println("What do you want to do? (add, subtract, multiply or divide?)");
String operator = scanner_all.nextLine();

switch (operator){

case "add": 
    System.out.println("Enter number one ");
    double addnum1 = scanner_all.nextDouble();
    System.out.println("Enter number two ");
    double addnum2 = scanner_all.nextDouble();
    System.out.print("the answer is: ");
    System.out.println( addnum1 + addnum2);
    break;

case "subtract": 
    System.out.println("Enter number one");
    double subnum1 = scanner_all.nextDouble();
    System.out.println("Enter number two ");
    double subnum2 = scanner_all.nextDouble();
    System.out.print("the answer is: ");
    System.out.println( subnum1 - subnum2 );
    break;

case "multiply": 
    System.out.println("Enter number one");
    double mulnum1 = scanner_all.nextDouble();
    System.out.println("Enter number two ");
    double mulnum2 = scanner_all.nextDouble();
    System.out.print("the answer is: ");
    System.out.println( mulnum1 * mulnum2 );
    break;
case "divide": 
    System.out.println("Enter number one");
    double divnum1 = scanner_all.nextDouble();
    System.out.println("Enter number two ");
    double divnum2 = scanner_all.nextDouble();
    System.out.print("the answer is: ");
    System.out.println( divnum1 / divnum2 );
    break;
}

第一次印刷

Scanner scanner3 = new Scanner(System.in);
String operator = scanner3.nextLine();

System.out.println("What do you want to do? (add, subtract, multiply, or divide?)");

switch (operator){

case "add": System.out.println("Enter number one ");
    Scanner scanner4 = new Scanner(System.in);
    double addnum1 = scanner4.nextDouble();
    System.out.println("Enter number two ");
    Scanner scanner5 = new Scanner(System.in);
    double addnum2 = scanner5.nextDouble();
    System.out.print("the answer is: ");
    System.out.println( addnum1 + addnum2);
    break;

case "subtract": System.out.println("Enter number one");
    Scanner scanner7 = new Scanner(System.in);
    double subnum1 = scanner7.nextDouble();
    System.out.println("Enter number two ");
    Scanner scanner8 = new Scanner(System.in);
    double subnum2 = scanner8.nextDouble();
    System.out.print("the answer is: ");
    System.out.println( subnum1 - subnum2 );
    break;

case "multiply": System.out.println("Enter number one");
    Scanner scanner9 = new Scanner(System.in);
    double mulnum1 = scanner9.nextDouble();
    System.out.println("Enter number two ");
    Scanner scanner10 = new Scanner(System.in);
    double mulnum2 = scanner10.nextDouble();
    System.out.print("the answer is: ");
    System.out.println( mulnum1 * mulnum2 );
    break;
case "divide": System.out.println("Enter number one");
    Scanner scanner11 = new Scanner(System.in);
    double divnum1 = scanner11.nextDouble();
    System.out.println("Enter number two ");
    Scanner scanner12 = new Scanner(System.in);
    double divnum2 = scanner12.nextDouble();
    System.out.print("the answer is: ");
    System.out.println( divnum1 / divnum2 );
    break;
}

System.out.println("What do you want to do? (add, subtract, multiply or divide?)");

是在

Scanner scanner3 = new Scanner(System.in);
String operator = scanner3.nextLine();

System.out.println("What do you want to do? (add, subtract, multiply, or divide?)");

switch (operator){

case "add": System.out.println("Enter number one ");
    Scanner scanner4 = new Scanner(System.in);
    double addnum1 = scanner4.nextDouble();
    System.out.println("Enter number two ");
    Scanner scanner5 = new Scanner(System.in);
    double addnum2 = scanner5.nextDouble();
    System.out.print("the answer is: ");
    System.out.println( addnum1 + addnum2);
    break;

case "subtract": System.out.println("Enter number one");
    Scanner scanner7 = new Scanner(System.in);
    double subnum1 = scanner7.nextDouble();
    System.out.println("Enter number two ");
    Scanner scanner8 = new Scanner(System.in);
    double subnum2 = scanner8.nextDouble();
    System.out.print("the answer is: ");
    System.out.println( subnum1 - subnum2 );
    break;

case "multiply": System.out.println("Enter number one");
    Scanner scanner9 = new Scanner(System.in);
    double mulnum1 = scanner9.nextDouble();
    System.out.println("Enter number two ");
    Scanner scanner10 = new Scanner(System.in);
    double mulnum2 = scanner10.nextDouble();
    System.out.print("the answer is: ");
    System.out.println( mulnum1 * mulnum2 );
    break;
case "divide": System.out.println("Enter number one");
    Scanner scanner11 = new Scanner(System.in);
    double divnum1 = scanner11.nextDouble();
    System.out.println("Enter number two ");
    Scanner scanner12 = new Scanner(System.in);
    double divnum2 = scanner12.nextDouble();
    System.out.print("the answer is: ");
    System.out.println( divnum1 / divnum2 );
    break;
}

.nextLine()

因此，您的程序在打印第一条消息之前需要输入

Scanner scanner3 = new Scanner(System.in);
String operator = scanner3.nextLine();

System.out.println("What do you want to do? (add, subtract, multiply, or divide?)");

switch (operator){

case "add": System.out.println("Enter number one ");
    Scanner scanner4 = new Scanner(System.in);
    double addnum1 = scanner4.nextDouble();
    System.out.println("Enter number two ");
    Scanner scanner5 = new Scanner(System.in);
    double addnum2 = scanner5.nextDouble();
    System.out.print("the answer is: ");
    System.out.println( addnum1 + addnum2);
    break;

case "subtract": System.out.println("Enter number one");
    Scanner scanner7 = new Scanner(System.in);
    double subnum1 = scanner7.nextDouble();
    System.out.println("Enter number two ");
    Scanner scanner8 = new Scanner(System.in);
    double subnum2 = scanner8.nextDouble();
    System.out.print("the answer is: ");
    System.out.println( subnum1 - subnum2 );
    break;

case "multiply": System.out.println("Enter number one");
    Scanner scanner9 = new Scanner(System.in);
    double mulnum1 = scanner9.nextDouble();
    System.out.println("Enter number two ");
    Scanner scanner10 = new Scanner(System.in);
    double mulnum2 = scanner10.nextDouble();
    System.out.print("the answer is: ");
    System.out.println( mulnum1 * mulnum2 );
    break;
case "divide": System.out.println("Enter number one");
    Scanner scanner11 = new Scanner(System.in);
    double divnum1 = scanner11.nextDouble();
    System.out.println("Enter number two ");
    Scanner scanner12 = new Scanner(System.in);
    double divnum2 = scanner12.nextDouble();
    System.out.print("the answer is: ");
    System.out.println( divnum1 / divnum2 );
    break;
}

您可以在所有情况下使用相同的扫描仪，更好、更干净的代码

Scanner scanner3 = new Scanner(System.in);
String operator = scanner3.nextLine();

System.out.println("What do you want to do? (add, subtract, multiply, or divide?)");

switch (operator){

case "add": System.out.println("Enter number one ");
    Scanner scanner4 = new Scanner(System.in);
    double addnum1 = scanner4.nextDouble();
    System.out.println("Enter number two ");
    Scanner scanner5 = new Scanner(System.in);
    double addnum2 = scanner5.nextDouble();
    System.out.print("the answer is: ");
    System.out.println( addnum1 + addnum2);
    break;

case "subtract": System.out.println("Enter number one");
    Scanner scanner7 = new Scanner(System.in);
    double subnum1 = scanner7.nextDouble();
    System.out.println("Enter number two ");
    Scanner scanner8 = new Scanner(System.in);
    double subnum2 = scanner8.nextDouble();
    System.out.print("the answer is: ");
    System.out.println( subnum1 - subnum2 );
    break;

case "multiply": System.out.println("Enter number one");
    Scanner scanner9 = new Scanner(System.in);
    double mulnum1 = scanner9.nextDouble();
    System.out.println("Enter number two ");
    Scanner scanner10 = new Scanner(System.in);
    double mulnum2 = scanner10.nextDouble();
    System.out.print("the answer is: ");
    System.out.println( mulnum1 * mulnum2 );
    break;
case "divide": System.out.println("Enter number one");
    Scanner scanner11 = new Scanner(System.in);
    double divnum1 = scanner11.nextDouble();
    System.out.println("Enter number two ");
    Scanner scanner12 = new Scanner(System.in);
    double divnum2 = scanner12.nextDouble();
    System.out.print("the answer is: ");
    System.out.println( divnum1 / divnum2 );
    break;
}

Scanner scanner_all = new Scanner(System.in);
System.out.println("What do you want to do? (add, subtract, multiply or divide?)");
String operator = scanner_all.nextLine();

switch (operator){

case "add": 
    System.out.println("Enter number one ");
    double addnum1 = scanner_all.nextDouble();
    System.out.println("Enter number two ");
    double addnum2 = scanner_all.nextDouble();
    System.out.print("the answer is: ");
    System.out.println( addnum1 + addnum2);
    break;

case "subtract": 
    System.out.println("Enter number one");
    double subnum1 = scanner_all.nextDouble();
    System.out.println("Enter number two ");
    double subnum2 = scanner_all.nextDouble();
    System.out.print("the answer is: ");
    System.out.println( subnum1 - subnum2 );
    break;

case "multiply": 
    System.out.println("Enter number one");
    double mulnum1 = scanner_all.nextDouble();
    System.out.println("Enter number two ");
    double mulnum2 = scanner_all.nextDouble();
    System.out.print("the answer is: ");
    System.out.println( mulnum1 * mulnum2 );
    break;
case "divide": 
    System.out.println("Enter number one");
    double divnum1 = scanner_all.nextDouble();
    System.out.println("Enter number two ");
    double divnum2 = scanner_all.nextDouble();
    System.out.print("the answer is: ");
    System.out.println( divnum1 / divnum2 );
    break;
}

---

你在顶部调用

nextLine（）

，所以它需要输入（甚至在打印任何东西之前）。你到底为什么要声明9-10扫描仪？？你在顶部调用

nextLine（）

，所以它需要输入（甚至在打印任何东西之前）。你到底为什么要声明9-10扫描仪？？