有一個找不到符號錯誤，另一個

Question

我得到2找不到符號錯誤，它似乎不是類路徑的結果。我也有一個問題，讓我的.add方法從listinterface.java代碼在我的pex6.java中工作。我不知道是否因爲即時通訊使用整數類型和添加方法是無效的，但我不知道。我現在已經用java工作了大約6個月，所以我對它仍然很陌生。讓我知道是否有遺漏。

public interface ListInterface<T> 
{ 


/** 
* Should return the number of elements contained within this list: 
*/`enter code here` 
int size(); 


/** 
* Should return true if this list contains a copy of the given object: 
* 
* Comparisons should be performed by calling the equals(...) method of 
* each element, passing the given object as an argument 
*/ 
boolean contains (T theObject); 


/** 
* Should remove the first element found within this list that exists as a 
* copy of the given object and return true if such an element was found: 
*/ 
boolean remove (T theObject); 


/** 
* Should return a reference to the first element found within this list 
* that exists as a copy of the given object or null if no such element was 
* found: 
*/ 
Object get (T element); 


/** 
* Should return a nicely formatted string representation of this list: 
*/ 
String toString(); 


/** 
* Should print the contents of this list to the screen: 
*/ 
void writeLinkedList(); 


/** 
* Should initialize this list for iteration (use of the getNext() method): 
*/ 
void reset(); 


/** 
* Should return a reference to the element located at the iterator's 
* current position and increment the iterator: 
* 
* If the iterator is currently pointing to the last element in this list, 
* the iterator should be reset to point to the first element in this list. 
* 
* @Preconditions: 
*  This list is not empty. 
*  This list has been reset. 
*  This list has not been modified since the last reset. 
*/ 
    T getNext(); 


/** 
* Should insert the given object onto the front of this list: 
*/ 
void add (T theObject); 

} 



public class PEX6 
{ 
public static void main (String[] theArgs) 
    { 
     ListInterface<String> list = new RefList<T>(); 


      for (int i = 1; i <= 20; i++); 
       { 
        int Random = ((int) (Math.random() * 4)); 
        list.add(new Integer(Random)); 

        list.writeLinkedList(); 
       } 
    } 
private static int CountValue(ListInterface<T> theList,int theValue) 
    { 
     theList.clear(); 
     Integer nFound = 20; 


     return nFound; 
    } 

} 

錯誤：

C:\Users\Linville\Documents\Assignment 6\PEX6.java:16: error: cannot find symbol 
    private static int CountValue(ListInterface<T> theList,int theValue) 
               ^
    symbol: class T 
    location: class PEX6 
C:\Users\Linville\Documents\Assignment 6\PEX6.java:5: error: cannot find symbol 
      ListInterface<String> list = new RefList<T>(); 
                ^
    symbol: class T 
    location: class PEX6 
C:\Users\Linville\Documents\Assignment 6\PEX6.java:11: error: method add in interface ListInterface<T> cannot be applied to given types; 
         list.add(new Integer(Random)); 
          ^
    required: String 
    found: Integer 
    reason: actual argument Integer cannot be converted to String by method invocation conversion 
    where T is a type-variable: 
    T extends Object declared in interface ListInterface 
3 errors 

Tool completed with exit code 1 

通過PEX6.java不以任何方式完成的方式，但我想先走，並得到正確的代碼編譯，所以我就不說了當我完成時，最終會有很多錯誤需要解決。

Answer 1

有一個在PEX6沒有T，但你指的是：

ListInterface<String> list = new RefList<T>(); 
             ^here 

private static int CountValue(ListInterface<T> theList,int theValue) 
              ^and here 

您需要任何String或Integer更換T。無法確定這兩者中的哪一個是有意的：您聲明list爲ListInterface<String>，然後繼續將Integers添加到它。

Answer 2

你需要傳遞一個類型爲T. 例如。如果你想ListInterface是一個字符串列表

private static int CountValue(ListInterface<String> theList,int theValue)