Java 在System.out.println中声明决策结构

所以我在做一个赋值，我必须在一个构造函数中有一个print方法来显示距离。 根据演示类中的输入，我还必须有三个单独的get方法。 我的问题是，我正在尝试编写print方法，以包含一个使用get的决策结构。 公共无效prt（）{ DecimalFormat formatter=新的DecimalFormat（“0.00”）

在尝试编译之后，我得到了以下错误

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

---

您的程序中可能有许多错误

1） 您没有

if

语句。这就是为什么在没有if的情况下出现

else错误的原因

2） 你最后说的是错的：

else
 "error";) 

您可以这样做：

 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");

或者更有效地像这样：-

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);

这一行的错误

 "error";)

检查这条线
你可以这样写

System.out.println("error");

您需要使用三元运算符
？：
而不是if/else

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

不能在
System.out.println
中使用这样的if语句

您可以使用做一些事情，但是为了代码可读性，最好只声明一个变量并像这样连接：

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);

不能这样做。请使用多个打印语句或一个变量。
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);