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我是一个编程新手，所以请多多包涵。我搜索并找不到可以回答这个问题的现有线程。我编写了以下代码，该代码应该根据安全对象是被用户识别为股票还是债券来吐出 stock.toString() 或 bond.toString() 罐头短语。但是，我收到“无法解决安全性”编译器错误。我想这是一个问题，因为安全对象的类不是在编译时定义的。真的吗？如果是这样，有什么办法可以在不诉诸反射方法的情况下解决这个问题？谢谢！

public static void main(String[] args) {

    double thePrice;
    double theShares;
    double theEarnings;
    double theRate;
    String securityType;

    Scanner in = new Scanner(System.in);

    System.out.println("Is it a stock or a bond?");
    securityType = in.nextLine();

    if (securityType.compareToIgnoreCase("stock") == 0) {
        System.out.println("Successfully set to STOCK");
        System.out.println("What are the earnings?");
        theEarnings = in.nextDouble();
        Stock security = new Stock();
        security.setEarnings(theEarnings);
    }

    else if (securityType.compareToIgnoreCase("bond") == 0) {
        System.out.println("Successfully set to BOND");
        System.out.println("What is the rate?");
        theRate = in.nextDouble();
        Bond security = new Bond();
        security.setRate(theRate);
    }

    System.out.println("What is the price");
    thePrice = in.nextDouble();     

    System.out.println("How many shares are there?");
    theShares = in.nextDouble();

    security.setPrice(thePrice);
    security.setShares(theShares);

    System.out.println(security);
}

感谢@Jigur Joshi、@penartur 和其他人。这是我们提出的解决方案，但如果有更好的选择，请告诉我。如果securityType既不是“股票”也不是“债券”，我正在添加一个else语句来清理:)

public static void main(String[] args) {

                ...
    Security security = null;
    String securityType;

    Scanner in = new Scanner(System.in);

    System.out.println("Is it a stock or a bond?");
    securityType = in.nextLine();

    System.out.println("What is the price"); 
    thePrice = in.nextDouble();      

    System.out.println("How many shares are there?"); 
    theShares = in.nextDouble(); 

    if (securityType.compareToIgnoreCase("stock") == 0) {
        System.out.println("Successfully registered STOCK");
        security = new Stock();
        System.out.println("What are the earnings?"); 
        theEarnings = in.nextDouble(); 
        ((Stock) security).setEarnings(theEarnings); 
    }

    if (securityType.compareToIgnoreCase("bond") == 0) {
        System.out.println("Successfully registered BOND");
        security = new Bond();
        System.out.println("What is the rate?"); 
        theRate = in.nextDouble(); 
        ((Bond) security).setRate(theRate);
    }

    security.setPrice(thePrice); 
    security.setShares(theShares); 

        System.out.println(security); 

}
4

3 回答 3

6

在 if else 之外声明它，以便在 if else 之后可用

假设Stock是 的超类Bond，如果不声明security为

 Object security = null;

做了

 Stock security = null;
 if (securityType.compareToIgnoreCase("stock") == 0) {
        System.out.println("Successfully set to STOCK");
        System.out.println("What are the earnings?");
        theEarnings = in.nextDouble();
        security = new Stock();
        security.setEarnings(theEarnings);
    }

    else if (securityType.compareToIgnoreCase("bond") == 0) {
        System.out.println("Successfully set to BOND");
        System.out.println("What is the rate?");
        theRate = in.nextDouble();
        security = new Bond();
        security.setRate(theRate);
    }

看

于 2012-06-29T05:03:43.683 回答
4

问题不在于类型。

您已经security在内部范围内定义了，它根本不存在于外部（您在哪里执行security.setPrice. 更糟糕的是，代码无法轻松修复，因为security根本不会定义（无论是否是内部范围）当securityType既不是“债券”也不是“股票”时。

但是我想你想要做的是：

public static void main(String[] args) {

    double thePrice;
    double theShares;
    double theEarnings;
    double theRate;
    String securityType;

    Scanner in = new Scanner(System.in);

    System.out.println("Is it a stock or a bond?");
    securityType = in.nextLine();

    System.out.println("What is the price");
    thePrice = in.nextDouble();     

    System.out.println("How many shares are there?");
    theShares = in.nextDouble();

    if (securityType.compareToIgnoreCase("stock") == 0) {
        System.out.println("Successfully set to STOCK");
        System.out.println("What are the earnings?");
        theEarnings = in.nextDouble();
        Stock security = new Stock();
        security.setEarnings(theEarnings);
        security.setPrice(thePrice);
        security.setShares(theShares);
        System.out.println(security);
    }

    else if (securityType.compareToIgnoreCase("bond") == 0) {
        System.out.println("Successfully set to BOND");
        System.out.println("What is the rate?");
        theRate = in.nextDouble();
        Bond security = new Bond();
        security.setRate(theRate);
        security.setPrice(thePrice);
        security.setShares(theShares);
        System.out.println(security);
    }

}

当然，这是一个糟糕的解决方案，但您必须首先澄清自己的任务。

于 2012-06-29T05:03:32.763 回答
1

问题出在变量的范围内。security仅在 if/else 块内定义。

您可以将代码更改为以下内容：

Object security; //you can use common superclass of Bond and Stock (maybe Security?)

if (securityType.compareToIgnoreCase("stock") == 0) {
    /* ... */
    Stock stock = new Stock();
    stock.setEarnings(theEarnings);
    security = stock;
}

else if (securityType.compareToIgnoreCase("bond") == 0) {
    /* ... */
    Bond bond = new Bond();
    bond.setRate(theRate);
    security = bond;
}

/* ... */
System.out.println(security);
于 2012-06-29T05:08:20.827 回答