diff --git a/src/chapter5/Example09.java b/src/chapter5/Example09.java
new file mode 100644
index 0000000..3e53434
--- /dev/null
+++ b/src/chapter5/Example09.java
@@ -0,0 +1,59 @@
+package chapter5;
+
+public class Example09 {
+    private static final int TIMES = 100000;
+
+    public static void main(String[] args) {
+        testString();
+        testStringBuffer();
+        testStringBuilder();
+        test();
+    }
+
+    // String时间效率
+    public static void testString() {
+        long start = System.currentTimeMillis();
+        String str = "";
+        for (int i = 0; i < TIMES; i++) {
+            str += "test";
+        }
+        long end = System.currentTimeMillis();
+        System.out.println("String测试耗时：" + (end - start) + "ms");
+    }
+
+    // StringBuffer时间效率（线程安全）
+    public static void testStringBuffer() {
+        long start = System.currentTimeMillis();
+        StringBuffer sb = new StringBuffer();
+        for (int i = 0; i < TIMES; i++) {
+            sb.append("test");
+        }
+        long end = System.currentTimeMillis();
+        System.out.println("StringBuffer测试耗时：" + (end - start) + "ms");
+    }
+
+    // StringBuilder时间效率（非线程安全）
+    public static void testStringBuilder() {
+        long start = System.currentTimeMillis();
+        StringBuilder sb = new StringBuilder("hello");
+        for (int i = 0; i < TIMES; i++) {
+            sb.append("test");
+        }
+        long end = System.currentTimeMillis();
+        System.out.println("StringBuilder测试耗时：" + (end - start) + "ms");
+    }
+
+    public static void test() {
+        String s1 = new String("abc");
+        String s2 = new String("abc");
+        System.out.println(s1.equals(s2));      // 打印结果为true
+        StringBuffer sb1 = new StringBuffer("abc");
+        StringBuffer sb2 = new StringBuffer("abc");
+        System.out.println(sb1.equals(sb2));   // 打印结果为false
+        StringBuilder sbr1=new StringBuilder("abc");
+        StringBuilder sbr2=new StringBuilder("abc");
+        System.out.println(sbr1.equals(sbr2));   // 打印结果为false
+
+    }
+
+}