diff --git a/notes/Java IO.md b/notes/Java IO.md
index ee23a4bb..acb95b36 100644
--- a/notes/Java IO.md	
+++ b/notes/Java IO.md	
@@ -182,8 +182,10 @@ public static void readFileContent(String filePath) throws IOException {
 
 ```java
 public static void main(String[] args) throws IOException, ClassNotFoundException {
+
     A a1 = new A(123, "abc");
     String objectFile = "file/a1";
+
     ObjectOutputStream objectOutputStream = new ObjectOutputStream(new FileOutputStream(objectFile));
     objectOutputStream.writeObject(a1);
     objectOutputStream.close();
@@ -195,6 +197,7 @@ public static void main(String[] args) throws IOException, ClassNotFoundExceptio
 }
 
 private static class A implements Serializable {
+
     private int x;
     private String y;
 
diff --git a/notes/Java 基础.md b/notes/Java 基础.md
index 5b689cf8..d8f17cef 100644
--- a/notes/Java 基础.md	
+++ b/notes/Java 基础.md	
@@ -685,26 +685,26 @@ protected void finalize() throws Throwable {}
 
 **1. 等价关系** 
 
-（一）自反性
+Ⅰ 自反性
 
 ```java
 x.equals(x); // true
 ```
 
-（二）对称性
+Ⅱ 对称性
 
 ```java
 x.equals(y) == y.equals(x); // true
 ```
 
-（三）传递性
+Ⅲ 传递性
 
 ```java
 if (x.equals(y) && y.equals(z))
     x.equals(z); // true;
 ```
 
-（四）一致性
+Ⅳ 一致性
 
 多次调用 equals() 方法结果不变
 
@@ -712,7 +712,7 @@ if (x.equals(y) && y.equals(z))
 x.equals(y) == x.equals(y); // true
 ```
 
-（五）与 null 的比较
+Ⅴ 与 null 的比较
 
 对任何不是 null 的对象 x 调用 x.equals(null) 结果都为 false
 
@@ -741,6 +741,7 @@ System.out.println(x == y);      // false
 
 ```java
 public class EqualExample {
+
     private int x;
     private int y;
     private int z;
diff --git a/notes/Java 虚拟机.md b/notes/Java 虚拟机.md
index 333c1418..2ad1527c 100644
--- a/notes/Java 虚拟机.md	
+++ b/notes/Java 虚拟机.md	
@@ -30,7 +30,7 @@
 
 # 一、运行时数据区域
 
-<div align="center"> <img src="../pics//c9ad2bf4-5580-4018-bce4-1b9a71804d9c.png" width="400"/> </div><br>
+<div align="center"> <img src="../pics//c9ad2bf4-5580-4018-bce4-1b9a71804d9c.png" width="450"/> </div><br>
 
 ## 程序计数器
 
@@ -40,7 +40,7 @@
 
 每个 Java 方法在执行的同时会创建一个栈帧用于存储局部变量表、操作数栈、常量池引用等信息。从方法调用直至执行完成的过程，就对应着一个栈帧在 Java 虚拟机栈中入栈和出栈的过程。
 
-<div align="center"> <img src="../pics//926c7438-c5e1-4b94-840a-dcb24ff1dafe.png" width="450"/> </div><br>
+<div align="center"> <img src="../pics//926c7438-c5e1-4b94-840a-dcb24ff1dafe.png" width="500"/> </div><br>
 
 可以通过 -Xss 这个虚拟机参数来指定每个线程的 Java 虚拟机栈内存大小：
 
diff --git a/notes/剑指 offer 题解.md b/notes/剑指 offer 题解.md
index 9d3ada1a..2c8f2822 100644
--- a/notes/剑指 offer 题解.md	
+++ b/notes/剑指 offer 题解.md	
@@ -1433,7 +1433,8 @@ public boolean IsPopOrder(int[] pushSequence, int[] popSequence) {
     Stack<Integer> stack = new Stack<>();
     for (int pushIndex = 0, popIndex = 0; pushIndex < n; pushIndex++) {
         stack.push(pushSequence[pushIndex]);
-        while (popIndex < n && stack.peek() == popSequence[popIndex]) {
+        while (popIndex < n && !stack.isEmpty() 
+                && stack.peek() == popSequence[popIndex]) {
             stack.pop();
             popIndex++;
         }