参考下面提供的代码，在main（）方法中，传递给static sort（）函数的实际参数的类型为String []（变量a），但sort（）函数的形式参数的类型为Comparable []。这怎么可能，因为这两种类型似乎与我不匹配？在我不知道的函数调用期间是否存在某种隐式对象转换？任何帮助，将不胜感激。
Merge.java
以下是来自§2.2Mergesort的Merge.java的语法高亮版本。
/******************************************************************************
* Compilation: javac Merge.java
* Execution: java Merge < input.txt
* Dependencies: StdOut.java StdIn.java
*
*
* Sorts a sequence of strings from standard input using mergesort.
*
* % more tiny.txt
* S O R T E X A M P L E
*
* % java Merge < tiny.txt
* A E E L M O P R S T X [ one string per line ]
*
* % more words3.txt
* bed bug dad yes zoo ... all bad yet
*
* % java Merge < words3.txt
* all bad bed bug dad ... yes yet zoo [ one string per line ]
*
******************************************************************************/
/**
* The {@code Merge} class provides static methods for sorting an
* array using mergesort.
* <p>
* For additional documentation, see <a href="http://algs4.cs.princeton.edu/22mergesort">Section 2.2</a> of
* <i>Algorithms, 4th Edition</i> by Robert Sedgewick and Kevin Wayne.
* For an optimized version, see {@link MergeX}.
*
* @author Robert Sedgewick
* @author Kevin Wayne
*/
public class Merge {
// This class should not be instantiated.
private Merge() { }
// stably merge a[lo .. mid] with a[mid+1 ..hi] using aux[lo .. hi]
private static void merge(Comparable[] a, Comparable[] aux, int lo, int mid, int hi) {
// precondition: a[lo .. mid] and a[mid+1 .. hi] are sorted subarrays
assert isSorted(a, lo, mid);
assert isSorted(a, mid+1, hi);
// copy to aux[]
for (int k = lo; k <= hi; k++) {
aux[k] = a[k];
}
// merge back to a[]
int i = lo, j = mid+1;
for (int k = lo; k <= hi; k++) {
if (i > mid) a[k] = aux[j++];
else if (j > hi) a[k] = aux[i++];
else if (less(aux[j], aux[i])) a[k] = aux[j++];
else a[k] = aux[i++];
}
// postcondition: a[lo .. hi] is sorted
assert isSorted(a, lo, hi);
}
// mergesort a[lo..hi] using auxiliary array aux[lo..hi]
private static void sort(Comparable[] a, Comparable[] aux, int lo, int hi) {
if (hi <= lo) return;
int mid = lo + (hi - lo) / 2;
sort(a, aux, lo, mid);
sort(a, aux, mid + 1, hi);
merge(a, aux, lo, mid, hi);
}
/**
* Rearranges the array in ascending order, using the natural order.
* @param a the array to be sorted
*/
public static void sort(Comparable[] a) {
Comparable[] aux = new Comparable[a.length];
sort(a, aux, 0, a.length-1);
assert isSorted(a);
}
/***************************************************************************
* Helper sorting function.
***************************************************************************/
// is v < w ?
private static boolean less(Comparable v, Comparable w) {
return v.compareTo(w) < 0;
}
/***************************************************************************
* Check if array is sorted - useful for debugging.
***************************************************************************/
private static boolean isSorted(Comparable[] a) {
return isSorted(a, 0, a.length - 1);
}
private static boolean isSorted(Comparable[] a, int lo, int hi) {
for (int i = lo + 1; i <= hi; i++)
if (less(a[i], a[i-1])) return false;
return true;
}
/***************************************************************************
* Index mergesort.
***************************************************************************/
// stably merge a[lo .. mid] with a[mid+1 .. hi] using aux[lo .. hi]
private static void merge(Comparable[] a, int[] index, int[] aux, int lo, int mid, int hi) {
// copy to aux[]
for (int k = lo; k <= hi; k++) {
aux[k] = index[k];
}
// merge back to a[]
int i = lo, j = mid+1;
for (int k = lo; k <= hi; k++) {
if (i > mid) index[k] = aux[j++];
else if (j > hi) index[k] = aux[i++];
else if (less(a[aux[j]], a[aux[i]])) index[k] = aux[j++];
else index[k] = aux[i++];
}
}
/**
* Returns a permutation that gives the elements in the array in ascending order.
* @param a the array
* @return a permutation {@code p[]} such that {@code a[p[0]]}, {@code a[p[1]]},
* ..., {@code a[p[N-1]]} are in ascending order
*/
public static int[] indexSort(Comparable[] a) {
int n = a.length;
int[] index = new int[n];
for (int i = 0; i < n; i++)
index[i] = i;
int[] aux = new int[n];
sort(a, index, aux, 0, n-1);
return index;
}
{
if (hi <= lo) return;
int mid = lo + (hi - lo) / 2;
sort(a, index, aux, lo, mid);
sort(a, index, aux, mid + 1, hi);
merge(a, index, aux, lo, mid, hi);
}
// print array to standard output
private static void show(Comparable[] a) {
for (int i = 0; i < a.length; i++) {
StdOut.println(a[i]);
}
}
/**
* Reads in a sequence of strings from standard input; mergesorts them;
* and prints them to standard output in ascending order.
*
* @param args the command-line arguments
*/
public static void main(String[] args) {
String[] a = StdIn.readAllStrings();
Merge.sort(a);
show(a);
}
}
答案 0 :(得分：0)
是否存在某种适用的隐式对象转换
投射不是您在对象上执行的操作，而是您对值执行的操作（例如对象参考）。 对象不受强制转换的影响。但是这里没有投射。
除了原始类型之外，如果类型为X，则可以为Y类型的变量或参数指定类型为Y的值：
X或class或X类型
X的子类或子接口。同样，如果X[]可以根据上述规则分配Y[]，则可以为数组类型X分配Y类型的值。
String实施Comparable，因此您可以将String分配给Comparable类型的变量或参数。由于数组类型可根据其元素类型进行分配，因此String[]可以分配给Comparable[]类型的变量或参数。
答案 1 :(得分：0)
这不是特定于函数调用：
Comparable comparable = "hello";
String[] strings = {"hello", "world"};
Comparable[] comparables = strings;
Java数组是协变的，这意味着如果数组的元素类型是可分配的。并且String可分配给Comparable，因为类String实现了Comparable接口。