[英]Generic Array Initialization in MergeSort
这是我的代码,用于实现通用合并排序。
import java.util.Arrays;
public class MergeSort<T extends Comparable<T>> {
public static void main(String[] args) {
Integer[] int_arr = { 10, 20, 35, 40, 13, 42 };
MergeSort<Integer> IntegerSort = new MergeSort<>();
IntegerSort.Merge_Sort(int_arr, 0, int_arr.length - 1);
System.out.println(Arrays.toString(int_arr));
}
private void Merge_Sort(T[] A, int low, int high) {
if (low < high) {
int mid = (low + high) / 2;
Merge_Sort(A, low, mid);
Merge_Sort(A, mid + 1, high);
Merge(A, low, mid, high);
}
}
private void Merge(T[] A, int low, int mid, int high) {
int n1 = mid - low + 1;
int n2 = high - mid;
T[] Left_sub = (T[]) new Object[n1];
T[] Right_sub = (T[]) new Object[n2];
for (int i = 0; i < n1; ++i) {
Left_sub[i] = A[low + i];
}
for (int j = 0; j < n2; ++j) {
Right_sub[j] = A[mid + j + 1];
}
int i = 0, j = 0;
for (int k = low; k < high; k++) {
if (less(Left_sub[i], Right_sub[j])) {
A[k] = Left_sub[i];
i = i + 1;
} else {
A[k] = Right_sub[j];
j = j + 1;
}
}
}
private boolean less(T v, T w) {
return v.compareTo(w) < 0;
}
}
我遇到了这个运行时错误
Exception in thread "main" java.lang.ClassCastException: class [Ljava.lang.Object; cannot be cast to class [Ljava.lang.Comparable; ([Ljava.lang.Object; and [Ljava.lang.Comparable; are in module java.base of loader 'bootstrap')
我错在
T[] Left_sub = (T[]) new Object[n1];
T[] Right_sub = (T[]) new Object[n2];
我尝试了其他方法,如Arrays.copyofrange()
、 ArrayList<T>
是否还有其他方法来初始化通用数组。 请建议在Merge()
函数中执行合并过程的方法。
要制作数组范围的副本,您应该使用Arrays.copyRangeOf
:
T[] Left_sub = Arrays.copyOfRange(A, low, mid + 1);
T[] Right_sub = Arrays.copyOfRange(A, mid, high + 1);
请注意这些注释:
high
参数容易出错,您应该使用下一个元素的索引,这样切片的长度就是high - low
。merge
方法,只复制切片的左侧部分,因为右侧部分的元素在复制之前不会被覆盖。这是一个修改后的版本:
import java.util.Arrays;
public class MergeSort<T extends Comparable<T>> {
public static void main(String[] args) {
Integer[] int_arr = { 10, 20, 35, 40, 13, 42 };
MergeSort<Integer> IntegerSort = new MergeSort<>();
IntegerSort.Merge_Sort(int_arr, 0, int_arr.length);
System.out.println(Arrays.toString(int_arr));
}
private void Merge_Sort(T[] A, int low, int high) {
if (high - low >= 2) {
int mid = low + (high - low) / 2; // avoid overfow or large values
Merge_Sort(A, low, mid);
Merge_Sort(A, mid, high);
Merge(A, low, mid, high);
}
}
private void Merge(T[] A, int low, int mid, int high) {
T[] Left_sub = Arrays.copyOfRange(A, low, mid);
int i = 0, j = mid, n1 = mid - low;
for (int k = low; k < high; k++) {
if (i < n1 && (j > high || Left_sub[i].compareTo(A[j]) <= 0)) {
A[k] = Left_sub[i++];
} else {
A[k] = A[j++];
}
}
}
}
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