Java 未定义此类型的方法

Java The method is undefined for this type

提问by Alex mesnier

I am having a problem with calling a method that is in a different class. This mainmethod is in a class on its own called lab14, and the heapSort()method is in a different class called HeapSort. Both of these classes are in the default package. I am getting the error "The method heapSort(Vector) is undefined for the type Lab14" and I don't understand why, please help.

我在调用不同类中的方法时遇到问题。这个main方法在一个类中单独调用lab14，而该heapSort()方法在另一个类中调用HeapSort。这两个类都在默认包中。我收到错误消息“未定义 Lab14 类型的 heapSort(Vector) 方法”，我不明白为什么，请帮忙。

below is the main method in the lab 14 class

下面是lab 14课的主要方法

public static void main(String args[]) {

    Heap myheap = new Heap();
    Vector<StudentGPA> vec = new Vector();
    int []  br = new int[20]; 
    double []  dr = new double[20]; 
    int i = 0;
    int j = 0;
    try {
    //String inputLine; //stores each line from the file
    Scanner scanLine;
    Scanner input = new Scanner(new File("students.in"));
    while (input.hasNextLine()){
    scanLine = new Scanner(input.nextLine());

    int id = scanLine.nextInt();
    //br[i] = id;
    String name = scanLine.next();
    double gpa = scanLine.nextDouble();
    //dr[i]= gpa;
    //myStr.add(name);
    if(scanLine.hasNext())
    {
         String advisor = scanLine.next();
         GraduateStudentGPA grad = new GraduateStudentGPA(id,name,gpa,advisor);
         vec.add(grad);
    }
    else
    {
        StudentGPA reg = new StudentGPA(id,name,gpa);
        vec.add(reg);
    }
    i++;
    j++;
    }
    input.close();
} 
catch (IOException e) {
    System.out.println("IOException in reading input file!!!"+e);
}   
heapSort(vec);
}

Below is the code for the HeapSort class

下面是 HeapSort 类的代码

public class HeapSort <E extends Comparable<? super E>>{
/** sorts the input vector using heap Sort <ul> <li> iterates
 * through each element of the input vector and inserts each
 * element to the heap by calling {\tt heapInsert}.  <li> deletes
 * each of the inserted items by calling {\tt heapDelete} the
 * appropriate number of times, and fills up the vector with the
 * returned elements.  </ul> If you are using the
 * minheap implementation, this insertion and deletion of all
 * items will produce a list of items sorted by their key
 * attribute values.
 * @param vec input vector
 */
public void heapSort(Vector<StudentGPA> vec){
    //  --  TO COMPLETE  --
    Heap myheap = new Heap<E>();
    for(int i = 0; i <vec.size(); i++)
    {
        myheap.heapInsert(vec.elementAt(i));
    }
    for(int i = 0; i <vec.size(); i++)
    {
        vec.setElementAt((StudentGPA) myheap.heapDelete(), i);
    }

}


}

回答by ssantos

You gave the answer:

你给出了答案：

you're trying to call heapSortmethod from Lab14class, but heapSortmethod is defined on a different class. The compilation error must be on this line.-

您试图heapSort从Lab14类中调用方法，但heapSort方法是在不同的类上定义的。编译错误必须在这一行。-

heapSort(vec);

You need to instantiate a HeapSort object, and then call its heapSortmethod like this.-

您需要实例化一个 HeapSort 对象，然后heapSort像这样调用它的方法。-

HeapSort myHeapSortObject = new HeapSort();
myHeapSortObject.heapSort(vec);

回答by pathfinderelite

Your heapsort method can be declared static, at least in its current state

您的 heapsort 方法可以声明为静态，至少在其当前状态下

public static <E extends Comparable<? super E>> void heapSort(Vector<StudentGPA> vec) {

You can then access it in your main method like this

然后你可以像这样在你的主方法中访问它

HeapSort.heapSort(vec);

回答by Toby Eggitt

You need to either:

您需要：

1) make the heapSort method public static... and invoke it as HeapSort.heapSort(vec)

1) 将 heapSort 方法设为 public static... 并将其作为 HeapSort.heapSort(vec) 调用

or 2) Invoke the method as new HeapSort().heapSort(vec)

或 2) 调用该方法作为 new HeapSort().heapSort(vec)

回答by YoYo

You have several issues going on here.

您在这里遇到了几个问题。

1. You call heapSort(vec);from within the static mainof class Lab14. This would mean that the compiler expects a method matching signature static void heapSort(Vector<StudentGPA> vec)within the Lab14class. Up to you how you solve that.
2. Change Vector<StudentGPA> vec = new Vector();into Vector<StudentGPA> vec = new Vector<>();. Note that addition of the angular brackets <>.
3. There are actually many more problems, possibly because it is still an unfinished work. Probably I should stay focused on your original question, for which 1./ is the answer.

1. 您heapSort(vec);从mainclass的静态内部调用Lab14。这意味着编译器需要static void heapSort(Vector<StudentGPA> vec)在Lab14类中匹配签名的方法。取决于你如何解决这个问题。
2. 更改Vector<StudentGPA> vec = new Vector();成Vector<StudentGPA> vec = new Vector<>();。注意角括号的添加<>。
3. 其实还有很多问题，可能是因为还没有完成。可能我应该专注于你最初的问题，1./ 是答案。