Java 跳过第三个 case 语句

Question

这是一个简单的计算器，我需要使用基本命令来运行它。这个项目的目标是对异常进行编程(非常简单)，但是，我一生都无法弄清楚这一点。我到处都找过了。

无论是 if/else 语句还是 Switch/Case 语句，第三条语句总是会被跳过。当用户输入“m”时，应该将计算值保存到占位符变量中以便能够调用(同样， super 简单)。我在添加部分添加了一个默认的 case 语句，并将我的保存方法添加到了默认语句中，它工作得很好。其他所有命令(r 表示重新调用，c 表示清除，e 表示退出)也很好用。 m 用于保 stub 本不......

import java.util.Scanner;

public class Calculator {
public static Scanner input = new Scanner(System.in);
public static double placeHolder;

public static void clear() {
    System.out.println("Save has been deleted, Screen has been cleared.");
}

public static void end() {
    System.out.println("Program ended..");
    input.close();
    System.exit(0);
}

public static void save(double initValue) {
    System.out.println("Number saved!");
    placeHolder = initValue;
}

public static void recall() {
    if (placeHolder != 0){
        System.out.println("Memory Place Holder Set To: " + placeHolder);
    }
    else {
        System.out.println("There is no data saved.");
    }
}

public static void commands() {
    System.out.println("e = end | c = clear | m = save | r = recall | o = continue");
    String command = input.nextLine();
    if (command.equals("e")){
        end();
    }
    else if (command.equals("c")){
        clear();
    }
    else if (command.equals("r")){
        recall();
    }

}




public static void main(String[] args) {
    boolean loop = true;
    while (loop == true){
        commands();
        System.out.println("Please enter what you would like to do: (+,-,*,/,%)");
        String function = input.nextLine();
        System.out.println("Enter the first number to be calucalted (If dividing, this is the numerator):");
        double n1 = input.nextDouble();
        System.out.println("Enter the second number to be calucalted (If dividing, this is the denominator):");
        double n2 = input.nextDouble();

        //=======================
        // Addition
        //=======================
        if (function.equals("+")){
            double sum = n1+n2;
            System.out.println(n1+"+"+ n2 +" = " + sum);
            System.out.println("e = end | c = clear | m = save | r = recall");
            String command = input.nextLine();
            input.nextLine();
            switch (command){
            case "e":
                end();
                break;
            case "c":
                clear();
                break;
            case "m":
                save(sum);
                break;
            case "r":
                recall();
                break;
            default: 
                System.out.println("Default");
                save(sum);
                break;
            }

        }
        //=======================
        // Subtraction
        //=======================
        else if (function.equals("-")){
            double sum = n1-n2;
            System.out.println(n1 + "-" + n2 +" = " + sum);
            System.out.println("e = end | c = clear | m = save | r = recall");
            String command = input.nextLine();
            input.nextLine();
            switch (command){
            case "e":
                end();
            case "c":
                clear();
            case "m":
                save(sum);
            case "r":
                recall();
            }
        }
        //=======================
        // Multiplication
        //=======================
        else if (function.equals("*")){
            double sum = n1*n2;
            System.out.println(n1 + "*" + n2 +" = " + sum);
            System.out.println("e = end | c = clear | m = save | r = recall");
            String command = input.nextLine();
            input.nextLine();
            switch (command){
            case "e":
                end();
            case "c":
                clear();
            case "m":
                save(sum);
            case "r":
                recall();
            }
        }
        //=======================
        // Division
        //=======================
        else if (function.equals("/")){
            double sum = n1/n2;
            System.out.println(n1 + "/" + n2 +" = " + sum);
            System.out.println("e = end | c = clear | m = save | r = recall");
            String command = input.nextLine();
            input.nextLine();
            switch (command){
            case "e":
                end();
            case "c":
                clear();
            case "m":
                save(sum);
            case "r":
                recall();
            }
        }
        //=======================
        // Mod
        //=======================
        else if (function.equals("%")){
            double sum = n1%n2;
            System.out.println(n1 + "%" + n2 +" = " + sum);
            System.out.println("e = end | c = clear | m = save | r = recall");
            String command = input.nextLine();
            input.nextLine();
            switch (command){
            case "e":
                end();
            case "c":
                clear();
            case "m":
                save(sum);
            case "r":
                recall();
            }
        }
    }   

        //=======================
        // Dictate loop duration:
        //=======================
        System.out.println("Would you like to continue? (Y|N): ");
        String ans = input.nextLine();
        if (ans.equals("N") || ans.equals("n")){
            System.out.println("Closing Program");
            loop = false;
            end();
        }
    }

}

有问题的主要代码是这样的:我知道其余的代码没有默认或中断语句。这个确实如此，我正在调试并试图找出 m 失败的原因。现在，如果你是他，它只会转到默认的 case 语句，这并不能解决问题。

 switch (command){
        case "e":
            end();
            break;
        case "c":
            clear();
            break;
        case "m":
            save(sum);
            break;
        case "r":
            recall();
            break;
        default: 
            System.out.println("Default");
            save(sum);
            break;

================================================== =========================以下是针对事后查看这篇文章的任何人的修复:

public static void main(String[] args) {
    boolean loop = true;
    while (loop == true){
        commands();
        System.out.println("Please enter what you would like to do: (+,-,*,/,%)");
        String function = input.nextLine();
        System.out.println("Enter the first number to be calucalted (If dividing, this is the numerator):");
        double n1 = input.nextDouble();
        input.nextLine();
        System.out.println("Enter the second number to be calucalted (If dividing, this is the denominator):");
        double n2 = input.nextDouble();
        input.nextLine();

        //=======================
        // Addition
        //=======================
        if (function.equals("+")){
            double sum = n1+n2;
            System.out.println(n1+"+"+ n2 +" = " + sum);
            System.out.println("e = end | c = clear | m = save | r = recall");
            String command = input.nextLine();
            switch (command){
            case "e":
                end();
                break;
            case "c":
                clear();
                break;
            case "m":
                save(sum);
                break;
            case "r":
                recall();
                break;
            }

        }

Answer 1

1. 在每次 input.nextDouble(); 之后，您需要调用 input.nextLine(); 来使用新行，请参阅 Scanner is skipping nextLine() after using next(), nextInt() or other nextFoo() methods
2. 删除每个 String command = input.nextLine(); 后不必要的 input.nextLine();