diff --git a/src/class42/CodeUtils.java b/src/class42/CodeUtils.java
new file mode 100644
index 0000000..a340bd0
--- /dev/null
+++ b/src/class42/CodeUtils.java
@@ -0,0 +1,35 @@
+package class42;
+
+public class CodeUtils {
+    public static String getCode(int n) {
+        StringBuilder code = new StringBuilder();
+        int Index;
+        for (int i = 0; i < n; i++){
+            //随机0-2
+            Index = (int)(Math.random() * 3);
+            switch ( Index){
+                case 0:
+                    code.append((char) (Math.random() * 26 + 'a'));
+                    break;
+                case 1:
+                    code.append((char) (Math.random() * 26 + 'A'));
+                    break;
+                case 2:
+                    code.append((int) (Math.random() * 10));
+                    break;
+            }
+        }
+        return code.toString();
+    }
+    public static String getCode2(int n){
+        String dict = "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ";
+        String code = "";
+        for (int i = 0; i < n; i++) {
+            int index = (int)(Math.random() * dict.length());
+            code += dict.charAt(index);
+        }
+        return code;
+    }
+
+
+}
diff --git a/src/class42/StringTest2.java b/src/class42/StringTest2.java
new file mode 100644
index 0000000..4c5643b
--- /dev/null
+++ b/src/class42/StringTest2.java
@@ -0,0 +1,17 @@
+package class42;
+
+public class StringTest2 {
+    public static void main(String[] args) {
+        String code= CodeUtils.getCode(4);
+
+        System.out.println(code);
+
+        String code2 = CodeUtils.getCode2(4);
+
+        System.out.println(code2);
+
+
+
+    }
+
+}