diff --git a/notes/设计模式.md b/notes/设计模式.md
index 9742e1b9..3e159d50 100644
--- a/notes/设计模式.md
+++ b/notes/设计模式.md
@@ -339,7 +339,7 @@ public class ConcreteFactory2 extends Factory {
 
 ### 类图
 
-<div align="center"> <img src="../pics//79076335-cfae-4fe6-97b9-62e8eebbf2b9.png"/> </div><br>
+<div align="center"> <img src="../pics//8668a3e1-c9c7-4fcb-98b2-a96a5d841579.png"/> </div><br>
 
 抽象工厂模式创建的是对象家族，也就是很多对象而不是一个对象，并且这些对象是相关的，也就是说必须一起创建出来。而工厂模式只是用于创建一个对象，这和抽象工厂模式有很大不同。
 
@@ -433,9 +433,83 @@ public class Client {
 
 ### 意图
 
-定义一个新的类来构造另一个类的实例，以创建一个复杂的对象。
+封装一个对象的构造过程，并允许按步骤构造。
 
-它可以封装一个对象的构造过程，并允许按步骤构造。
+### 类图
+
+<div align="center"> <img src="../pics//13b0940e-d1d7-4b17-af4f-b70cb0a75e08.png"/> </div><br>
+
+### 实现
+
+以下是一个简易的 StringBuilder 实现，参考了 JDK 1.8 源码。
+
+```java
+public class AbstractStringBuilder {
+    protected char[] value;
+
+    protected int count;
+
+    public AbstractStringBuilder(int capacity) {
+        count = 0;
+        value = new char[capacity];
+    }
+
+    public AbstractStringBuilder append(char c) {
+        ensureCapacityInternal(count + 1);
+        value[count++] = c;
+        return this;
+    }
+
+    private void ensureCapacityInternal(int minimumCapacity) {
+        // overflow-conscious code
+        if (minimumCapacity - value.length > 0)
+            expandCapacity(minimumCapacity);
+    }
+
+    void expandCapacity(int minimumCapacity) {
+        int newCapacity = value.length * 2 + 2;
+        if (newCapacity - minimumCapacity < 0)
+            newCapacity = minimumCapacity;
+        if (newCapacity < 0) {
+            if (minimumCapacity < 0) // overflow
+                throw new OutOfMemoryError();
+            newCapacity = Integer.MAX_VALUE;
+        }
+        value = Arrays.copyOf(value, newCapacity);
+    }
+}
+```
+
+```java
+public class StringBuilder extends AbstractStringBuilder {
+    public StringBuilder() {
+        super(16);
+    }
+
+    @Override
+    public String toString() {
+        // Create a copy, don't share the array
+        return new String(value, 0, count);
+    }
+}
+```
+
+```java
+public class Client {
+    public static void main(String[] args) {
+        StringBuilder sb = new StringBuilder();
+        final int count = 26;
+        for (int i = 0; i < count; i++) {
+            sb.append((char) ('a' + i));
+        }
+        System.out.println(sb.toString());
+    }
+}
+```
+
+```html
+abcdefghijklmnopqrstuvwxyz
+```
 
 ### JDK
 
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