This article mainly introduces the case of Java List sort() method rewriting compare() to achieve ascending, descending, and reverse order. It has good reference value and I hope it will be helpful to everyone. Let's follow the editor to take a look
This article aims to realize the ascending, descending, and reverse sorting of the List by rewriting the compare() method of the Comparator interface.
First, make it clear: In
compare(Integer o1, Integer o2){}, o1 represents the next element in the List container, and o2 represents the previous element in the List container!
This can be clearly understood through the following examples:
public static void main(String[] args) {
List<Integer> list = new ArrayList<Integer>();
list.add(1);
list.add(2);
list.add(3);
list.sort(new Comparator<Integer>() {
public int compare(Integer o1, Integer o2) {
System.out.println(o1 + "," + o2);//输出o1,o2
return 0;
}
});
}
The output is:
-
2，1
-
3，2
Ascending
code:
public static void main(String[] args) {
List<Integer> list = new ArrayList<Integer>();
list.add(1);
list.add(2);
list.add(3);
list.sort(new Comparator<Integer>() {
public int compare(Integer o1, Integer o2) {
if(o1>o2)
return 1;//第二个元素（o1）比第一个元素（o2）大，返回1
if(o1==o2)
return 0;
return -1;
}//1,0,-1三者同时出现时，1表示不交换位置，0表示相等时不交换，-1表示交换
});
System.out.println(list.toString());
}
Output:
[1,2,3]
Descending
code:
public static void main(String[] args) {
List<Integer> list = new ArrayList<Integer>();
list.add(1);
list.add(2);
list.add(3);
list.sort(new Comparator<Integer>() {
public int compare(Integer o1, Integer o2) {
if(o1>o2)
return -1;//第二个元素（o1）比第一个元素（o2）大，返回-1
if(o1==o2)
return 0;
return 1;
}//1,0,-1三者同时出现时，1表示不交换位置，0表示相等时不交换，-1表示交换
});
System.out.println(list.toString());
Output:
[3,2,1]
Reverse
code:
public static void main(String[] args) {
List<Integer> list = new ArrayList<Integer>();
list.add(1);
list.add(2);
list.add(3);
list.sort(new Comparator<Integer>() {
public int compare(Integer o1, Integer o2) {
return -1;
}//倒序就直接返回-1
});
System.out.println(list.toString());
}
Output:
[3,2,1]
Supplement: Sample code for ordering, reverse order, and random sorting of elements in the List collection in Java
I won't talk too much nonsense, everyone should look at the code directly~
import java.util.Collections;
import java.util.LinkedList;
import java.util.List;
public class Test {
List list = new LinkedList();
public static void main(String[] args) {
List list = new LinkedList();
for ( int i = 0 ; i < 9 ; i ++ ) {
list.add( " a " + i);
}
Collections.sort(list); // 顺序排列
System.out.println(list);
Collections.shuffle(list); // 混乱的意思
System.out.println(list);
Collections.reverse(list); // 倒序排列
System.out.println(list);
System.out.println(Collections.binarySearch(list, " a5 " )); // 折半查找
}
}
Supplement: java8 is sorted according to two fields (one positive order and one reverse)
List<Student> collect2 = list.stream()
.sorted(Comparator.comparing(Student::getAge).reversed().thenComparing(Student::getScore))
.collect(Collectors.toList());
The above is personal experience, I hope to give you a reference, and I hope you can support the editor. If there are mistakes or not fully considered, please feel free to enlighten me