Question

String car; 

    if (type == 'E')
        {fee = rate*50;
         car = "Economy";}

    else if (type == 'M')
         {fee = rate*70;
         car = "Midsize";}


    else if (type == 'F')
        {fee = rate*100;
        car = "Fullsize";}

System.out.println("Car type is " + car);

这是我遇到问题的程序的一部分。我得到'本地变量车可能尚未初始化'。我应该怎么做才能让'汽车'初始化？

Answer 1

Java不能保证car将被初始化。您else声明中指定if的个案（car）没有保证。

将其初始化为某个值，例如空字符串。

String car = "";

Answer 2

通常，您将String设置为null以解决编译错误。

String car = null;

这是因为Java试图保护你不要做你不期望的事情。如果未执行所有if语句，则不会分配变量。要告诉Java，您知道可能会发生这种情况，您只需明确选择将其设置为null。

Answer 3

Java无法分辨你的变量覆盖打印会发生什么，因为它最初指向无处，并且条件中包含了进一步的初始化根据逻辑将您的汽车变量设置为默认值：“”或null是不错的选项，但它最终取决于您

Answer 4

我会考虑以另一种方式做到这一点：

switch (type) {
 case 'E':
    fee =rate* 50;
    car = "Economy";
    break;
 case 'M':
    fee =rate* 70;
    car = "Economy";
    break;
 case 'F':
    fee =rate*100;
    car = "Economy";
    break;
 default:
    fee = 0;
    car = "";
}

Answer 5

如何使用内部Enum类解决此问题。

public class EnumExample {
    public enum CarType {
        E( 50,"Economy" ),
        F( 70, "Midsize" ),
        M( 100, "Fullsize");
        // Add as many as you want

        private int cost;
        private String type;

        CarType(int theCost, String theType) {
            cost = theCost;
            type = theType;
        }

        public int getFee(int rate) {
            return rate*cost;
        }

        public String toString() {
            return type;
        }
    }
    public static void main( String[] args ) {
        String type = "E";
        int rate = 25;

        switch( CarType.valueOf( type ) ) {
            case E:
                System.out.println( "The Car Type is: " + CarType.E );
                System.out.println( "The fee is: " + CarType.E.getFee(rate) );
                break;
            case F:
                System.out.println( "The Car Type is: " + CarType.F );
                System.out.println( "The fee is: " + CarType.F.getFee(rate) );
                break;
            case M:
                // ETC
            default:
                // Use a switch/case so you can add 'no car type' e.g Fee = 0;
        }
    }
}

如何初始化字符串？

5 个答案: