diff --git a/day07/src/com/inmind/arraylist03/Demo12.java b/day07/src/com/inmind/arraylist03/Demo12.java
index 2e3cbf3..363d43b 100644
--- a/day07/src/com/inmind/arraylist03/Demo12.java
+++ b/day07/src/com/inmind/arraylist03/Demo12.java
@@ -1,11 +1,27 @@
 package com.inmind.arraylist03;
+
+import java.util.ArrayList;
+
 /*
 常用类-ArrayList-练习2_添加对象
  */
 public class Demo12 {
     public static void main(String[] args) {
         //创建一个保存学生对象的集合
+        ArrayList<Student> students = new ArrayList<>();
         //往集合中保存3个学生对象
+        Student s1 = new Student(1, 20, "刘备");
+        Student s2 = new Student(2, 21, "关羽");
+        Student s3 = new Student(3, 22, "张飞");
+
+        students.add(s1);
+        students.add(s2);
+        students.add(s3);
+        
         //对集合进行遍历打印学生的学号，年龄和姓名（直接获取属性打印，也可以封装为方法调用）
+        for (int i = 0; i < students.size(); i++) {
+            Student s = students.get(i);
+            s.show();
+        }
     }
 }
diff --git a/day07/src/com/inmind/arraylist03/Demo13.java b/day07/src/com/inmind/arraylist03/Demo13.java
new file mode 100644
index 0000000..5e4e7bd
--- /dev/null
+++ b/day07/src/com/inmind/arraylist03/Demo13.java
@@ -0,0 +1,41 @@
+package com.inmind.arraylist03;
+
+import java.util.ArrayList;
+
+/*
+14.常用类-ArrayList-练习3_指定格式拼接字符串
+定义以指定格式打印集合的方法(ArrayList类型作为参数)，使用@分隔每个元素。并返回
+格式参照 [元素@元素@元素]。
+ */
+public class Demo13 {
+    public static void main(String[] args) {
+        //2.在主方法中调用该方法，获取内容，打印输出
+        ArrayList<String> list = new ArrayList<>();
+        list.add("张三");
+        list.add("李四");
+        list.add("关羽");
+        list.add("刘备");
+        list.add("王五");
+        String result = printList(list);
+        System.out.println(result);
+
+    }
+
+    //1.定义一个方法，作用将对应的集合的内容，获取出来，拼接成[元素@元素@元素]，返回
+    public static String printList(ArrayList<String> list){
+        String result = "[";
+
+        for (int i = 0; i < list.size(); i++) {
+            String temp = list.get(i);
+            //如果是最后一个拼接]否则是@
+            if (i == list.size() - 1) {
+                result += temp + "]";
+            } else {
+                result += temp + "@";
+            }
+        }
+
+        return result;
+    }
+
+}
diff --git a/day07/src/com/inmind/arraylist03/Demo14.java b/day07/src/com/inmind/arraylist03/Demo14.java
new file mode 100644
index 0000000..b839372
--- /dev/null
+++ b/day07/src/com/inmind/arraylist03/Demo14.java
@@ -0,0 +1,9 @@
+package com.inmind.arraylist03;
+/*
+常用类-ArrayList-练习4_获取偶数集合
+实现方式2种：
+    1.创建新的集合只保存偶数
+    2.不创建新的集合，只把原集合中不为偶数的数据删除掉即可
+ */
+public class Demo14 {
+}
diff --git a/day07/src/com/inmind/arraylist03/Student.java b/day07/src/com/inmind/arraylist03/Student.java
index ffe398a..ac293b3 100644
--- a/day07/src/com/inmind/arraylist03/Student.java
+++ b/day07/src/com/inmind/arraylist03/Student.java
@@ -47,4 +47,9 @@ public class Student {
     public void study(String book) {
         System.out.println("在学习");
     }
+
+    public void show(){
+        String showStr = "学号为"+this.getId()+",年龄为"+age+"，姓名为"+this.name;
+        System.out.println(showStr);
+    }
 }