diff --git a/src/main/java/com/github/hcsp/collection/Main.java b/src/main/java/com/github/hcsp/collection/Main.java
index ae0f842..a7c0337 100644
--- a/src/main/java/com/github/hcsp/collection/Main.java
+++ b/src/main/java/com/github/hcsp/collection/Main.java
@@ -1,12 +1,15 @@
 package com.github.hcsp.collection;
 
-import java.util.Arrays;
-import java.util.List;
-import java.util.Set;
+import java.util.*;
 
 public class Main {
     // 请编写一个方法，获得a和b集合中的公共元素。
-    public static Set<Person> commonElementsIn(List<Person> a, List<Person> b) {}
+    public static Set<Person> commonElementsIn(List<Person> a, List<Person> b) {
+        ArrayList<Person> personsOne = new ArrayList<>(a);
+        ArrayList<Person> personsTwo = new ArrayList<>(b);
+        personsOne.retainAll(personsTwo);
+        return new HashSet<>(personsOne);
+    }
 
     // Person类，如果两个Person对象的name相等，则认为这两个对象相等。
     public static class Person {
@@ -23,11 +26,28 @@ public String getName() {
         public void setName(String name) {
             this.name = name;
         }
+
+        @Override
+        public boolean equals(Object obj) {
+            if(obj instanceof Person) {
+                Person person = (Person) obj;
+                return this.getName().equals(person.getName());
+            }
+            return false;
+        }
+
+
+        @Override
+        public int hashCode() {
+            return Objects.hash(name);
+        }
     }
 
     public static void main(String[] args) {
         List<Person> list1 = Arrays.asList(new Person("张学友"), new Person("周杰伦"));
         List<Person> list2 = Arrays.asList(new Person("周润发"), new Person("周杰伦"));
+        System.out.println(list1);
+        System.out.println(list2);
         System.out.println(commonElementsIn(list1, list2));
     }
 }
diff --git a/src/test/java/com/github/hcsp/collection/MainTest.java b/src/test/java/com/github/hcsp/collection/MainTest.java
index 1697f32..271fbf9 100644
--- a/src/test/java/com/github/hcsp/collection/MainTest.java
+++ b/src/test/java/com/github/hcsp/collection/MainTest.java
@@ -1,10 +1,11 @@
 package com.github.hcsp.collection;
 
+import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.Test;
+
 import java.util.Arrays;
 import java.util.HashSet;
 import java.util.List;
-import org.junit.jupiter.api.Assertions;
-import org.junit.jupiter.api.Test;
 
 public class MainTest {
     @Test