2012-04-07 107 views
1

我正在創建一個通用的多路樹,我知道將只採用四種類型之一(整數,雙精度,字符串和字符)。我在可比接口和插入功能方面遇到問題。下面是相關的代碼到目前爲止,我已經寫了:Multiway樹可比較的接口問題

public class BTree<T extends Comparable<? super T>> 
{ 
    private int m=0, height=0, numkeys=0; 
    private BTreeNode<T> root; 
    boolean ready=false; 

class BTreeNode<T extends Comparable<? super T>> 
{ 
    boolean leaf = true; 
    int keyTally = 1; 
    Comparable<T> keys[] = new Comparable[m-1]; 
    BTreeNode<T> references[] = new BTreeNode[m]; 
    BTreeNode(T key) 
    { 
     keys[0] = (Comparable<T>) key; 
     for (int i=0; i<m; i++) 
      references[i] = null; 
    } 
} 

public BTree(int c) 
{ 
    root=null; 
    m=c; 
} 

// Not finished - can't test due to other bug 
public boolean insertElement(T elem) 
{ 
    insert(elem, root, height); 
    numkeys++; 
    return true; 
} 

// And now the ploblem function 

private BTreeNode<T> insert(T elem, BTreeNode<T> node, int hvar) 
{ 
    int i; 

    BTreeNode<T> temp = null; 

    if (hvar == 0) 
    { 
     for (i = 0; i < node.keyTally; i++) 
      if (elem.compareTo(node.keys[i]) < 0) 
       break; 
    } 
    else 
    { 
     for (i = 0; i < node.keyTally; i++) 
     { 
      if ((i+1 == node.keyTally) || elem.compareTo(node.keys[i]) < 0) 
      { 
       Node n = insert(elem, node.references[i++], hvar-1); 
       if (n == null) 
        return null; 

       temp.keys[0] = n.keys[0]; 
       temp.references[0] = n; 
       break; 
      } 
     } 
    } 

    for (int j = node.keyTally; j > i; j--) 
     node.keys[j] = node.keys[j-1]; 
    node.children[i] = temp; 
    node.keyTally++; 
    if (node.keyTally < m) 
     return null; 
    else 
    { 
     BTreeNode<T> newNode = null; 
     newNode.keyTally = m/2; 
     for(i=0; i<m/2; i++) 
     newNode.references[i] = node.references[m/2+i]; 
     return newNode; 
    } 
    return null; 
} 

,這裏是我的控制檯輸出:

BTree.java:169: error: method compareTo in interface Comparable<T#2> cannot be applied 
to given types; 
if (elem.compareTo(node.keys[i]) < 0) 
     ^
required: CAP#1 
found: Comparable<T#1> 
reason: actual argument Comparable<T#1> cannot be converted to CAP#1 by method 
invocation conversion 
where T#1,T#2 are type-variables: 
T#1 extends Comparable<? super T#1> declared in class BTree 
T#2 extends Object declared in interface Comparable 
where CAP#1 is a fresh type-variable: 
CAP#1 extends Object super: T#1 from capture of ? super T#1 

BTree.java:176: error: method compareTo in interface Comparable<T#2> cannot be 
applied to given types; 
if ((i+1 == node.keyTally) || elem.compareTo(node.keys[i]) < 0) 
           ^
required: CAP#1 
found: Comparable<T#1> 
reason: actual argument Comparable<T#1> cannot be converted to CAP#1 by 
method invocation conversion 
where T#1,T#2 are type-variables: 
T#1 extends Comparable<? super T#1> declared in class BTree 
T#2 extends Object declared in interface Comparable 
where CAP#1 is a fresh type-variable: 
CAP#1 extends Object super: T#1 from capture of ? super T#1 

BTree.java:178: error: cannot find symbol 
Node n = insert(elem, node.references[i++], hvar-1); 
^ 
symbol: class Node 
location: class BTree<T> 
where T is a type-variable: 
T extends Comparable<? super T> declared in class BTree 

BTree.java:191: error: cannot find symbol 
node.children[i] = temp; 
    ^
symbol: variable children 
location: variable node of type BTree<T>.BTreeNode<T> 
where T is a type-variable: 
T extends Comparable<? super T> declared in class BTree 

Note: Some input files use unchecked or unsafe operations. 
Note: Recompile with -Xlint:unchecked for details. 
4 errors 

我不明白我在做什麼毛病可比接口,使其抱怨關於compareTo方法。另外,我想知道如果使用字符串類型會做什麼?我認爲它會按字母順序查看哪一個先到達。謝謝:)

回答

1

這是因爲node.keys[i]是類型Comparable<T>而不是T。反過來嘗試比較。

+0

謝謝您的回覆!我只需將'elem.compareTo(node.keys [i])'改爲'node.keys [i] .compareTo(elem)' – Tim 2012-04-07 17:35:56

1

我建議你無論是從Comparable<T>[]改變keys類型T[](因爲這是要爲使用它是什麼,你就必須要小心,從來不將其返回到的類外);或者您每次獲得某些東西時都手動投射到T(T)node.keys[i]