JAVA---编译器和运行时错误.类主

Question

/* Airport class
   Anderson, Franceschi
*/

public class Airport
{
    public static void main(String[] args)
    {
// 1. ***** Define the instance variables  *****
// airportCode is a String
// gates is an integer
// Part 1 student code starts here:

    private String airportCode;
    private int gates;

// Part 1 student code ends here.
// 2. ***** Write this method *****
// Default constructor:
// method name: Airport
// return value:  none
// parameters: none
// function: sets the airportCode to an empty String
// Part 2 student code starts here:
    public Airport()
    {
        airportCode = "";
    }

// Part 2 student code ends here.
// 3. ***** Write this method *****
// Overloaded constructor:
// method name: Airport
// return value: none
// parameters:  a String startAirportCode and an int startGates
// function:
//      calls the the setAirportCode method,
//                   passing startAirportCode parameter;
//      calls the setGates method, passing the startGates parameter
// Part 3 student code starts here:
    public Airport(String startAirportCode, int startGates)
    {
        setAirportCode(startAirportCode);
        setGates(startGates);
    }
// Part 3 student code ends here.
// 4. ***** Write this method *****
// Accessor method for the airportCode instance variable
// method name: getAirportCode
// return value: String
// parameters: none
// function: returns airportCode
// Part 4 student code starts here:
    public String getAirportCode()
    {
        return airportCode;
    }

// Part 4 student code ends here.
// 5. ***** Write this method *****
// Accessor method for the gates instance variable
// method name: getGates
// return value: int
// parameters: none
// function: returns gates
// Part 5 student code starts here:
    public int getGates()
    {
        return gates;
    }

// Part 5 student code ends here.
// 6. ***** Write this method *****
// Mutator method for the airportCode instance variable
// method name: setAirportCode
// return value: void
// parameters: String newAirportCode
// function: assigns airportCode the value of the
//                    newAirportCode parameter
// Part 6 student code starts here:
    public void setAirportCode(String newAirportCode)
    {
      airportCode = newAirportCode;
    }

// Part 6 student code ends here.
// 7. ***** Write this method *****
// Mutator method for the gates instance variable
// method name: setGates
// return value:  void
// parameters: int newGates
// function: validates the newGates parameter.
//   if newGates is greater than or equal to 0,
//       sets gates to newGates;
//       otherwise, prints an error message to System.err
//        and does not change value of gates
// Part 7 student code starts here:
    public void setGates(int newGates)
    {
        if (newGates >= 0)
        gates = newGates;
    else
        {
            System.err.println("Gates must be at least 0.");
            System.err.println("Value of gates unchanged.");
            return;
        }


    /*public void setGates(int newGates)
    {
        newGates = gates;
    }
*/
// Part 7 student code ends here.
    enter code here
}  // end of Airport class definition
}

书中的代码不包含公共静态 void main(String[] args(。一旦我搜索了该网站，我还是添加了它，它说你不能用最近的 java 更新做到这一点。在没有 main 语句的情况下，我让它成功编译，但有一个运行时错误，说"在机场类中找不到 main 方法"。我添加了它并遇到了一些编译器错误。我玩了一下花括号，最终打破了它......现在我不知道为什么我会得到 23 个合成错误。

我正在使用Java外部工具在文本板中编码。它适用于主类和 StackFlow 的方法，但并非没有主类 - 仍然说它找不到该类。我从实例变量中删除了"私有"。它在没有它的情况下成功编译，但仍然存在上述运行时错误。这个文件并没有真正运行，但它将与另一个为我编码的框架一起使用。这只是第 1 部分;第 2 部分的基础。

对于其他询问我的人，我相信它"仅适用于 java 1.6 或更低版本"Java 程序如何在不定义 main 方法的情况下运行？

再次感谢大家的帮助。这个网站真棒！

Answer 1

这应该可以解开(但不能修复(这一点：

public class Airport
{
public static void main(String[] args)
{
  System.out.println("Running. But what do I have to do?");
} //CLOSE THAT MAIN <- need to close that method.
[... all you code ...]
}  // end of Airport class definition
//Remove this. Class already ended. }

从那里开始，你应该做两件事：找出main((中应该发生什么，并安装一个带有语法高亮和eclipse之类的IDE。这将为您指出这些类型的错误。

Answer 2

你不能做

 public static void main(String[] args)
 {
    private String airportCode;
    private int gates;
 }

你的变量在主函数之外或将它们声明为局部变量。在启动其他函数之前，您还需要关闭 main。

您更正的代码如下所示：

/* Airport class
   Anderson, Franceschi
*/

public class Airport
{
    public static void main(String[] args)
    {
    }
// 1. ***** Define the instance variables  *****
// airportCode is a String
// gates is an integer
// Part 1 student code starts here:
    private String airportCode;
    private int gates;

// Part 1 student code ends here.
// 2. ***** Write this method *****
// Default constructor:
// method name: Airport
// return value:  none
// parameters: none
// function: sets the airportCode to an empty String
// Part 2 student code starts here:
    public Airport()
    {
        airportCode = "";
    }

// Part 2 student code ends here.
// 3. ***** Write this method *****
// Overloaded constructor:
// method name: Airport
// return value: none
// parameters:  a String startAirportCode and an int startGates
// function:
//      calls the the setAirportCode method,
//                   passing startAirportCode parameter;
//      calls the setGates method, passing the startGates parameter
// Part 3 student code starts here:
    public Airport(String startAirportCode, int startGates)
    {
        setAirportCode(startAirportCode);
        setGates(startGates);
    }
// Part 3 student code ends here.
// 4. ***** Write this method *****
// Accessor method for the airportCode instance variable
// method name: getAirportCode
// return value: String
// parameters: none
// function: returns airportCode
// Part 4 student code starts here:
    public String getAirportCode()
    {
        return airportCode;
    }

// Part 4 student code ends here.
// 5. ***** Write this method *****
// Accessor method for the gates instance variable
// method name: getGates
// return value: int
// parameters: none
// function: returns gates
// Part 5 student code starts here:
    public int getGates()
    {
        return gates;
    }

// Part 5 student code ends here.
// 6. ***** Write this method *****
// Mutator method for the airportCode instance variable
// method name: setAirportCode
// return value: void
// parameters: String newAirportCode
// function: assigns airportCode the value of the
//                    newAirportCode parameter
// Part 6 student code starts here:
    public void setAirportCode(String newAirportCode)
    {
      airportCode = newAirportCode;
    }

// Part 6 student code ends here.
// 7. ***** Write this method *****
// Mutator method for the gates instance variable
// method name: setGates
// return value:  void
// parameters: int newGates
// function: validates the newGates parameter.
//   if newGates is greater than or equal to 0,
//       sets gates to newGates;
//       otherwise, prints an error message to System.err
//        and does not change value of gates
// Part 7 student code starts here:
    public void setGates(int newGates)
    {
        if (newGates >= 0)
        gates = newGates;
    else
        {
            System.err.println("Gates must be at least 0.");
            System.err.println("Value of gates unchanged.");
            return;
        }


    /*public void setGates(int newGates)
    {
        newGates = gates;
    }
*/
// Part 7 student code ends here.
    enter code here
}

机场类定义结束 }

Answer 3

这可能会

有所帮助!!正如上面有人所说，

你的变量在主函数之外或将它们声明为局部变量。在启动其他函数之前，您还需要关闭 main。

public class Airport
{  
String airportCode;
int gates;
public Airport()
{
    airportCode = "";
}
public Airport(String startAirportCode, int startGates)
{
    setAirportCode(startAirportCode);
    setGates(startGates);
}
public String getAirportCode()
{
    return airportCode;
}

public int getGates()
{
    return gates;
}

public void setAirportCode(String newAirportCode)
{
  airportCode = newAirportCode;
}
public void setGates(int newGates)
{
    if (newGates >= 0)
    gates = newGates;
else
    {
        System.err.println("Gates must be at least 0.");
        System.err.println("Value of gates unchanged.");
        return;
    }
}
public static void main(String[] args) {
    Airport r = new Airport("Hello", 1);
    r.setAirportCode("Abcd");
    System.out.println("" + r.getAirportCode());
    r.setGates(3);
    System.out.println("" + r.getGates());
}
}

Answer 4

你不需要 main 方法。 如果删除这些行：

public static void main(String[] args)
    {

并在底部注释掉这一行：

enter code here

它应该编译：javac Airport.java 。 这个机场对象听起来像是你不运行的东西......只要建造它，它就会表现得像一个机场。 我猜在课程的后面，你会制作一些使用机场的东西......就像机场模拟器.java。 它可能有一个 main 方法，看起来像这样：

public class AirportSimulator
{
    public static void main(String[] args)
    {
        AirportSimulator airsim = new AirportSimulator();
        airsim.simulate();
    }
    public void simulate()
    {
        Airport air = new Airport();
        System.out.println("Setting gates to 1");
        air.setGates(1);
        System.out.println(String.format("Gates set to %d", air.getGates());
        System.out.println("Setting airport code to IAD");
        air.setAirportCode("IAD");
        System.out.println(String.format("Airport code is %s", air.getAirportCode());
    }
}

我的观点是，模拟器就像一个动词，更有意义，你可以用一个主线运行它，而机场就像一个名词。