在Java中使用switch的问题

Question

我不知道为什么它总是返回arg1的值。 我正在建立一个体重转换器。

public double convert(double arg1,int arg2,int arg3) {
    // arg1 = amount, arg2 = from, arg3 = to
    double milligram = 1;
    double gram = 1000;
    double ounce = 28349.5;
    double pound = 453592;
    double answer = 0;
    switch(arg2) {
    case 0: switch(arg3) { // if milligram
            case 0: answer = (arg1 * milligram) / milligram;
            case 1: answer = (arg1 * milligram) / gram;
            case 2: answer = (arg1 * milligram) / ounce;
            case 3: answer = (arg1 * milligram) / pound;
    }
    case 1: switch(arg3) { // if gram
            case 0: answer = (arg1 * gram) / milligram;
            case 1: answer = (arg1 * gram) / gram;
            case 2: answer = (arg1 * gram) / ounce;
            case 3: answer = (arg1 * gram) / pound;
    }
    case 2: switch(arg3) { // if ounce
            case 0: answer = (arg1 * ounce) / milligram;
            case 1: answer = (arg1 * ounce) / gram;
            case 2: answer = (arg1 * ounce) / ounce;
            case 3: answer = (arg1 * ounce) / pound;
    }
    case 3: switch(arg3) { // if pound
            case 0: answer = (arg1 * pound) / milligram;
            case 1: answer = (arg1 * pound) / gram;
            case 2: answer = (arg1 * pound) / ounce;
            case 3: answer = (arg1 * pound) / pound;
    }
    } // end arg2 switch
    return answer;
}

我弄乱了逻辑，但看不到哪里。 任何帮助，将不胜感激。

Answer 1

您缺少break语句：

case 0: 
   answer = (arg1 * milligram) / milligram;
   break;
   ...

Answer 2

像这样重写每种情况

case 2: switch(arg3) { // if ounce
        case 0: answer = (arg1 * ounce) / milligram;break;
        case 1: answer = (arg1 * ounce) / gram;break;
        case 2: answer = (arg1 * ounce) / ounce;break;
        case 3: answer = (arg1 * ounce) / pound;break;

Answer 3

嵌套的case语句很难阅读，也很难调试。 最好将所需的功能封装到方法调用中。

话虽如此，您的交换机中任何地方都没有break语句。 无论大小写如何，它都会落到最后一个大小写（将答案设置为等于大小写的底端）。

Answer 4

您应该使用break in switch语句，否则结果可能会被破坏

Answer 5

除了使用break ，使用return语句不仅可以达到目的，而且还可以防止失败。

case 2: switch(arg3) { // if ounce
    case 0: return (arg1 * milligram) / milligram;