我正在创建一个通用的多路树,我知道它只会采用四种类型中的一种(整数,双精度,字符串和字符)。我遇到类似的界面和插入功能的问题。这是我到目前为止所写的相关代码:
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;
}
这是我的控制台输出:
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
我不明白我在使用类似的界面做错了什么让它抱怨compareTo方法。另外,我想知道如果使用字符串类型会怎么做?我假设它会按字母顺序看哪一个按顺序排在第一位。谢谢:))
答案 0 :(得分:1)
这是因为node.keys[i]
的类型为Comparable<T>
,而非T
。反过来尝试比较。
答案 1 :(得分:1)
我建议您将keys
的类型从Comparable<T>[]
更改为T[]
(因为这是您想要使用它的;您只需要小心,不要把它归还给班级外面);或者每当你从中获取某些东西时手动转换为T
:(T)node.keys[i]