在我的main方法中，我收到错误消息不兼容的类型。 我创建了一个printList方法来打印输出。我认为问题与这种方法有关，但到目前为止我无法弄明白。
import java.io.File;
import java.io.FileNotFoundException;
import java.util.ArrayList;
import java.util.Scanner;
public class Sort
{
/* fun printList list =
let
val counter = ref 0
val temp = ref ""
val n = length(list)
in
while (!counter < n) do
( temp := !temp ^ (Int.toString(List.nth(list,!counter))^" ");
counter := !counter+1);
temp := !temp ^ "\n";
!temp
end;
*/
public static String printList (ArrayList<Integer> left)
{
int counter = 0;
String temp = "";
int n = left.size();
while(counter < n)
{
temp += left.get(counter)+ " ";
counter += 1;
}
temp += "\n";
return temp;
}
/*
fun lineList file =
let
val instr = TextIO.openIn file
val str = TextIO.input instr
in
String.tokens (fn x => x = #",")str
before
TextIO.closeIn instr
end;
*/
public ArrayList<Integer> lineList(String file) throws FileNotFoundException
{
ArrayList<Integer> tmp = new ArrayList();
try {
Scanner scanner = new Scanner(new File(file));
scanner.useDelimiter(",");
int i = 0;
while (scanner.hasNextInt()) {
tmp.add(scanner.nextInt());
i++;
}
scanner.close();
} catch (FileNotFoundException e) {
e.printStackTrace();
}
return tmp;
}
/*
fun halve nil = (nil, nil)
| halve [a] = ([a], nil)
| halve (a :: b :: cs) =
let
val (x, y) = halve cs
in
(a :: x, b :: y)
end;
*/
public static ArrayList<Integer> halve(ArrayList<Integer> l, String subL){
int halveSize = l.size() / 2;
ArrayList<Integer> halfList = new ArrayList<Integer>(halveSize);
if(subL == "left"){
for(int i = 0; i < l.size(); i += 2){
halfList.add(l.get(i));
}
}else if(subL == "right"){
for(int i = 1; i < l.size(); i += 2){
halfList.add(l.get(i));
}
}
return halfList;
}
/*
fun merge (nil, ys) = ys
| merge (xs, nil) = xs
| merge (x :: xs, y :: ys) =
if (x > y) then x :: merge(xs, y :: ys)
else y :: merge(x :: xs, ys);
*/
public static ArrayList<Integer> merge(ArrayList<Integer> le, ArrayList<Integer> r) {
ArrayList<Integer> result = new ArrayList<Integer>();
int i = 0;
int j = 0;
while (i < le.size() && j < r.size()) {
if (le.get(i) <= r.get(j)) {
result.add(le.get(i));
i++;
}else {
result.add(r.get(j));
j++;
}
}
for (int k=0;k<le.size();k++) {
if (k>i) {
result.add(le.get(k));
}
}
for (int l=0;l<r.size();l++) {
if (l>j) {
result.add(r.get(l));
}
}
return result;
}
/*
fun mergeSort nil = nil
| mergeSort [a] = [a]
| mergeSort theList =
let
val (x, y) = halve theList
in
print("xList: "^printList(x));
print("yList: "^printList(y));
merge(mergeSort x, mergeSort y)
end;
*/
public static ArrayList<Integer> mergeSort(ArrayList<Integer> l){
if(l.size() <= 1){
return l;
}
ArrayList<Integer> xList = halve(l, "left");
ArrayList<Integer> yList = halve(l, "right");
System.out.print("xList: " +printList(xList));
System.out.print("yList: " +printList(yList));
return merge(mergeSort(xList), mergeSort(yList));
}
/*
fun quicksort nil = nil
| quicksort (pivot :: rest) =
let
fun split(nil) = (nil,nil)
| split(x :: xs) =
let
val (below, above) = split(xs)
in
if x < pivot then (x :: below, above)
else (below, x :: above)
end;
val (below, above) = split(rest)
in
quicksort below @ [pivot] @ quicksort above
end;
val optList = map (fn str => (Int.fromString str)) (lineList "/home/chella/Documents/SMLCode1/input.txt");
val intList = map Option.valOf optList;
fun uselessMachine x = mergeSort(quicksort(x));
uselessMachine(intList);
*/
public static ArrayList<Integer> quickSort(ArrayList<Integer> input)
{
if(input.size() <= 1){
return input;
}
int centre = input.get(0);
ArrayList<Integer> a = new ArrayList<Integer>();
ArrayList<Integer> b = new ArrayList<Integer>();
for(int i = 1; i < input.size(); i++){
if(input.get(i) < centre){
a.add(input.get(i));
}else{
b.add(input.get(i));
}
}
ArrayList<Integer> output = quickSort(a);
output.add(centre);
output.addAll(quickSort(b));
return output;
}
public static void main(String[] args)
{
//Sort <Integer>s= new Sort<Integer>();
Sort s= new Sort ();
//int [] a = {1,2,3,4,8,10};
//System.out.println(s.printList(a));
try {
s.mergeSort(s.quickSort(s.lineList("input.txt")));
System.out.println(printList(s));
} catch (FileNotFoundException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
答案 0 :(得分：2)
错误信息非常清楚......
排序无法转换为java.util.arraylist
问题出在这一行：
System.out.println(printList(s));
s是Sort的实例
Sort s = new Sort();
虽然printList的签名是
public static String printList (ArrayList<Integer> left)
假设接收ArrayList<Integer>而不是Sort对象。
我认为您想要使用的是
System.out.println(printList(s.lineList("input.txt")));
这将解决错误。
编辑：以下是我在评论中讨论的片段：
Sort s = new Sort();
ArrayList<Integer> a = new ArrayList<Integer>();
a.add(1);
a.add(2);
a.add(3);
a.add(4);
a.add(8);
a.add(10);
System.out.println(printList(a));
此外，如果您想以reverse顺序打印，则必须使用list方法中的Collections包来反转printList现在看起来像这个：
public static String printList (ArrayList<Integer> left)
{
int counter = 0;
String temp = "";
int n = left.size();
Collections.reverse(left);
while(counter < n)
{
temp += left.get(counter)+ " ";
counter += 1;
}
temp += "\n";
return temp;
}
输出将为10 8 4 3 2 1