diff --git a/pom.xml b/pom.xml
index 86a2927..3dae4a9 100644
--- a/pom.xml
+++ b/pom.xml
@@ -64,6 +64,11 @@
             <version>5.6.0</version>
             <scope>test</scope>
         </dependency>
+        <dependency>
+            <groupId>com.google.guava</groupId>
+            <artifactId>guava</artifactId>
+            <version>32.1.3-jre</version>
+        </dependency>
     </dependencies>
 
     <build>
diff --git a/src/main/java/com/github/hcsp/polymorphism/Point.java b/src/main/java/com/github/hcsp/polymorphism/Point.java
index 780e6b1..f402035 100644
--- a/src/main/java/com/github/hcsp/polymorphism/Point.java
+++ b/src/main/java/com/github/hcsp/polymorphism/Point.java
@@ -1,5 +1,4 @@
 package com.github.hcsp.polymorphism;
-
 import java.io.IOException;
 import java.util.Arrays;
 import java.util.List;
@@ -8,6 +7,7 @@ public class Point {
 
     private final int x;
     private final int y;
+
     // 代表笛卡尔坐标系中的一个点
     public Point(int x, int y) {
         this.x = x;
@@ -22,6 +22,7 @@ public int getY() {
         return y;
     }
 
+
     @Override
     public boolean equals(Object o) {
         if (this == o) {
@@ -53,7 +54,16 @@ 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) {
+        points.sort((p1, p2) -> {
+            if (p1.getX() != p2.getX()) {
+                return Integer.compare(p1.getX(), p2.getX());
+            } else {
+                return Integer.compare(p1.getY(), p2.getY());
+            }
+        });
+        return points;
+    }
 
     public static void main(String[] args) throws IOException {
         List<Point> points =
@@ -66,3 +76,4 @@ public static void main(String[] args) throws IOException {
         System.out.println(Point.sort(points));
     }
 }
+