Question

所以我正在进行一项任务，我必须在显示距离的构造函数中使用print方法。我还必须有三个单独的get方法，具体取决于demo类中的输入。我的问题是我正在尝试编写print方法以包含一个基于get使用的决策结构。 public void prt（）{ DecimalFormat formatter = new DecimalFormat（＆＃34;＃，## 0.00＆＃34;）;

    System.out.println(
        "The time it takes the sound to travel " + distance +
         " feet through air is " + 

            if (getSpeedInAir() > 0) {
                formatter.format(getSpeedInAir());
            }

            else if (getSpeedInWater() > 0) {
                formatter.format(getSpeedInWater());
            }

            else if (getSpeedInSteel() > 0) {
                formatter.format(getSpeedInSteel());
            }

            else "error";
    ) 
}

尝试编译后，我收到以下错误。

Microsoft Windows [Version 6.1.7601]
Copyright (c) 2009 Microsoft Corporation.  All rights reserved.

C:\Users\GlaDOS\Desktop\JavaStuff>j Speed

C:\Users\GlaDOS\Desktop\JavaStuff>del    *.class

C:\Users\GlaDOS\Desktop\JavaStuff>javac  Speed.java
Speed.java:43: error: illegal start of expression
                                                           " feet through air is
 " + if (getSpeedInAir() > 0)

     ^
Speed.java:43: error: ';' expected
                                                           " feet through air is
 " + if (getSpeedInAir() > 0)

       ^
Speed.java:43: error: not a statement
                                                           " feet through air is
 " + if (getSpeedInAir() > 0)

                         ^
Speed.java:43: error: ';' expected
                                                           " feet through air is
 " + if (getSpeedInAir() > 0)

                            ^
Speed.java:47: error: 'else' without 'if'

                                 else if (getSpeedInWater() > 0)

                                 ^
Speed.java:56: error: not a statement

                                   "error";)

                                   ^
Speed.java:56: error: illegal start of expression

                                   "error";)

                                           ^
7 errors

C:\Users\GlaDOS\Desktop\JavaStuff>java   Speed
Error: Could not find or load main class Speed

Answer 1

您的计划可能存在很多错误。

1）你没有if陈述。这就是为什么你得到else without if。

的错误

2）你最后别的错了：

else
 "error";)

你可以这样尝试：

 if(getSpeedInAir() > 0)
 {
    System.out.println("The time it takes the sound to travel " + distance +
                           " feet through air is " +formatter.format(getSpeedInAir());
 }
 else if (getSpeedInWater() > 0)
 {
   System.out.println("The time it takes the sound to travel " + distance +
                           " feet through air is " + formatter.format(getSpeedInWater());
 }
else if (getSpeedInSteel() > 0)
{
  System.out.println("The time it takes the sound to travel " + distance +
                           " feet through air is " + formatter.format(getSpeedInSteel());
}
 else
   System.out.println("The time it takes the sound to travel " + distance +
                           " feet through air is "+ "error");

或更有效地这样： -

String s;
if (getSpeedInAir() > 0)
{
    s= formatter.format(getSpeedInAir()).toString();
}
else if (getSpeedInWater() > 0)
{
    s= formatter.format(getSpeedInWater()).toString();
}
else if (getSpeedInSteel() > 0)
{
    s= formatter.format(getSpeedInSteel()).toString();
}
else
    s= "error";

System.out.println("The time it takes the sound to travel " + distance +
                           " feet through air is " + s);

Answer 2

此行中的错误

 "error";)

检查此行你可能会写这样的东西

System.out.println("error");

Answer 3

您需要使用三元运算符?:而不是if / else

... " feet through air is " + (getSpeedInAir() > 0 ? : formatter.format(getSpeedInAir()) ...

Answer 4

您不能在System.out.println内使用if语句。

你可以对ternary operator做一些事情，但为了代码可读性，最好只是声明一个变量并连接如下：

String speed;
if (getSpeedInAir() > 0)
{
    speed = formatter.format(getSpeedInAir()).toString();
}
else if (getSpeedInWater() > 0)
{
    speed = formatter.format(getSpeedInWater()).toString();
}
else if (getSpeedInSteel() > 0)
{
    speed = formatter.format(getSpeedInSteel()).toString();
}
else
    speed = "error";

System.out.println("The time it takes the sound to travel " + distance +
                           " feet through air is " + speed);

在System.out.println中声明决策结构

4 个答案: