Java：如何对自定义类型 ArrayList 进行排序
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Java: How to sort custom type ArrayList
提问by atom2ueki
I have a custom type Position(x,y,z),now I create a ArrayList<Position>, i want to sort this array ordered by the value of z, from small to bigger,how can i do that using Collections.sortor is there any other efficient sorting method?
我有一个自定义类型Position(x,y,z)，现在我创建了一个ArrayList<Position>，我想按 z 的值排序这个数组，从小到大，我该如何使用Collections.sort或者是否有任何其他有效的排序方法？
When I try to use
当我尝试使用
public class PositionComparator implements Comparator<Position> {
@Override
public int compare(Position o1, Position o2) {
// TODO Auto-generated method stub
return o1.height().compareTo(o2.height());
}
}
get an error
得到一个错误
Cannot invoke compareTo(double) on the primitive type double
回答by Adam Siemion
You need to implement your Comparator, which will compare the value of the zattribute.
您需要实现您的Comparator，它将比较z属性的值。
回答by upog
try
尝试
Collections.sort(SortList, new Comparator<Position>(){
public int compare(Position p1, Position p2) {
return p1.z- p2.z;
}
});
回答by sunysen
Collections.sort
for example
例如
class 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;
}
}
import java.util.Comparator;
public class ComparatorUser implements Comparator {
public int compare(Object arg0, Object arg1) {
User user0 = (User) arg0;
User user1 = (User) arg1;
int flag = user0.getAge().compareTo(user1.getAge());
if (flag == 0) {
return user0.getName().compareTo(user1.getName());
} else {
return flag;
}
}
}
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);
for (int i = 0; i < userlist.size(); i++) {
User user_temp = (User) userlist.get(i);
System.out.println(user_temp.getAge() + "," + user_temp.getName());
}
}
}
回答by alex
I use this (just an example I cut and past but same idea) for descending sort:
我使用这个（只是我删减和过去但同样的想法的一个例子）进行降序排序：
@Override
public int compare(Member m1, Member m2) {
double fit1 = m1.getFitness() ;
double fit2 = m2.getFitness() ;
if (fit2>fit1)
return 1;
else if (fit2<fit1)
return -1;
else
return 0;
}
