java array List排序
在java 中 对list排序用
//Collections.sort( userlist, comparator);
Collections.sort (userlist);
// User 类需要继承实现Comparable
对数组排序可直接用：
Arrays. sort(intArray );
package
com.czy.sort;
public
class
User
implements
Comparable<User> {
String
name
;
String
age
;
public
User(String name, String age) {
this
.
name
= name;
this
.
age
= age;
}
public
String getAge() {
return
age
;
}
public
void
setAge(String age) {
this
.
age
= age;
}
public
String getName() {
return
name
;
}
public
void
setName(String name) {
this
.
name
= name;
}
@Override
public
int
compareTo(User user) {
int
flag =
this
.getAge().compareTo(user.getAge());
if
(flag == 0) {
return
this
.getName().compareTo(user.getName());
}
else
{
return
flag;
}
}
}
package
com.czy.sort;
import
java.util.Comparator;
public
class
ComparatorUser
implements
Comparator{
public
int
compare(Object arg0, Object arg1) {
User user0 = (User ) arg0;
User user1 = (User ) arg1;
// 首先比较年龄，如果年龄相同，则比较名字
int
flag = user0.getAge().compareTo(user1.getAge());
if
(flag == 0) {
return
user0.getName().compareTo(user1.getName());
}
else
{
return
flag;
}
}
}
package
com.czy.sort;
import
java.util.ArrayList;
import
java.util.Collections;
import
java.util.List;
public
class
SortTest {
public
static
void
main(String[] args) {
List userlist =
new
ArrayList();
userlist.add(
new
User(
"dd"
,
"4"
));
userlist.add(
new
User(
"aa"
,
"1"
));
userlist.add(
new
User(
"ee"
,
"5"
));
userlist.add(
new
User(
"bb"
,
"2"
));
userlist.add(
new
User(
"ff"
,
"5"
));
userlist.add(
new
User(
"cc"
,
"3"
));
userlist.add(
new
User(
"gg"
,
"6"
));
//ComparatorUser comparator = new ComparatorUser();
//Collections.sort( userlist, comparator);
Collections.sort (userlist);
// User 类需要继承实现Comparable
for
(
int
i = 0; i < userlist.size(); i++) {
User user_temp = (User) userlist.get(i);
System.
out
.println(user_temp.getAge() +
","
+ user_temp.getName());
}
}
}
在java 内部 还是将list 转换成array，然后再对数组进行排序
Object[] a = list.toArray();
Arrays. sort(a);
ListIterator<T> i = list.listIterator();
for
(
int
j=0; j<a.
length
; j++) {
i.next();
i.set((T)a[j]);
}
再看 sort：
public
static
void
sort(Object[] a) {
Object[] aux = (Object[])a.clone();
mergeSort(aux, a, 0, a.
length
, 0);
}
再看 mergeSort（归并排序）：
private
static
void
mergeSort (Object[] src,
Object[] dest,
int
low,
int
high,
int
off) {
int
length = high - low;
// Insertion sort on smallest arrays
if
(length <
INSERTIONSORT_THRESHOLD
) {
for
(
int
i=low; i<high; i++)
for
(
int
j=i; j>low &&
((Comparable) dest[j-1]).compareTo(dest[j])>0; j--)
swap(dest, j, j-1);
return
;
}
// Recursively sort halves of dest into src
int
destLow = low;
int
destHigh = high;
low += off;
high += off;
int
mid = (low + high) >>> 1;
mergeSort(dest, src, low, mid, -off);
mergeSort(dest, src, mid, high, -off);
// If list is already sorted, just copy from src to dest. This is an
// optimization that results in faster sorts for nearly ordered lists.
if
(((Comparable)src[mid-1]).compareTo(src[mid]) <= 0) {
System. arraycopy(src, low, dest, destLow, length);
return
;
}
// Merge sorted halves (now in src) into dest
for
(
int
i = destLow, p = low, q = mid; i < destHigh; i++) {
if
(q >= high || p < mid && ((Comparable)src[p]).compareTo(src[q])<=0)
dest[i] = src[p++];
else
dest[i] = src[q++];
}
}