diff --git a/src/main/java/com/github/hcsp/polymorphism/Point.java b/src/main/java/com/github/hcsp/polymorphism/Point.java
index 780e6b1..dbd5f0d 100644
--- a/src/main/java/com/github/hcsp/polymorphism/Point.java
+++ b/src/main/java/com/github/hcsp/polymorphism/Point.java
@@ -2,9 +2,10 @@
 
 import java.io.IOException;
 import java.util.Arrays;
+import java.util.Collections;
 import java.util.List;
 
-public class Point {
+public class Point implements Comparable<Point>{
 
     private final int x;
     private final int y;
@@ -53,7 +54,10 @@ public String toString() {
 
     // 按照先x再y，从小到大的顺序排序
     // 例如排序后的结果应该是 (-1, 1) (1, -1) (2, -1) (2, 0) (2, 1)
-    public static List<Point> sort(List<Point> points) {}
+    public static List<Point> sort(List<Point> points) {
+        Collections.sort(points);
+        return points;
+    }
 
     public static void main(String[] args) throws IOException {
         List<Point> points =
@@ -65,4 +69,21 @@ public static void main(String[] args) throws IOException {
                         new Point(2, -1));
         System.out.println(Point.sort(points));
     }
+
+    @Override
+    public int compareTo(Point point) {
+        if(this.x<point.x){
+            return -1;
+        }
+        if(this.x>point.x){
+            return 1;
+        }
+        if(this.y<point.y){
+            return -1;
+        }
+        if(this.y>point.y){
+            return 1;
+        }
+        return 0;
+    }
 }