java - printf 不适用于字符串

Question

我试图让这个 printf 工作，但我不断收到一个异常，提示第一个 '%' 运算符。我像这样多次使用 printf，从来没有遇到过问题。我正在使用 eclipse 。

我的问题:

为什么我的语句不起作用，我怎样才能让它起作用？

注意事项:

第18行，第二个%用来表示一个文字%

printf 语句:

14 System.out.printf("Symbol: %s\n"
15      + "Name: %s\n"
16      + "Previous Closing Price: %1.2f\n"
17      + "Current Price: %1.2f\n"
18      + "Change: %1.2f%", 
19      stock.symbol, 
20      stock.name, 
21      stock.previousClosingPrice,
22      stock.currentPrice,
23      stock.getChangePercent());

错误:

Exception in thread "main" java.util.UnknownFormatConversionException: Conversion = '%'
    at java.util.Formatter.checkText(Unknown Source)
    at java.util.Formatter.parse(Unknown Source)
    at java.util.Formatter.format(Unknown Source)
    at java.io.PrintStream.format(Unknown Source)
    at java.io.PrintStream.printf(Unknown Source)
    at No8_2.main(No8_2.java:14)

值(value)观:

(不一定是程序中的实际代码)

stock.symbol = "ORCL";
stock.name = "Oracle Corporation";
stock.previousClosingPrice = 34.5;
stock.currentPrice = 34.35;

'股票'类:

class Stock{
    //Stock Object
    String symbol;
    String name;
    double previousClosingPrice;
    double currentPrice;

    Stock(String sym, String nam){
        //Initialize Instance Vars
        this.symbol = sym;
        this.name = nam;
    }

    public double getChangePercent(){
        //Return (in %) the change in price
        return ((currentPrice - previousClosingPrice)/previousClosingPrice)*100;
    }
}

免责声明:这是一项家庭作业，但我已经为它完整地编写了代码。我只需要克服这个错误，并获得我的导师的许可，就可以发布这样的问题。

Answer 1

The second % is intentional, to turn 14.5 into 14.5%

您需要使用第二个 % 转义 %:

System.out.printf("Symbol: %s\n"
      + "Name: %s\n"
      + "Previous Closing Price: %1.2f\n"
      + "Current Price: %1.2f\n"
      + "Change: %1.2f%%", 
      //               ^
      stock.symbol, 
      stock.name, 
      stock.previousClosingPrice,
      stock.currentPrice,
      stock.getChangePercent());

另见 https://docs.oracle.com/javase/8/docs/api/java/util/Formatter.html :

In general, the format specifier has the following syntax:

%[argument_index$][flags][width][.precision]conversion

The following table summarizes the supported conversions:

...
'%'   percent The result is a literal '%' ('\u0025')
...