feat(class43): ArrayList 集合（泛型类）示例

- 新增 ArrayListDemo1.java 文件，演示 ArrayList 的基本操作
- 在 StringTest2.java 中添加字节数组转换为字符串的示例代码

src/class42/StringTest2.java

@@ -1,5 +1,7 @@
 package class42;
 
+import java.util.Arrays;
+
 public class StringTest2 {
     public static void main(String[] args) {
         String code= CodeUtils.getCode(4);
@@ -10,8 +12,20 @@ public class StringTest2 {
 
         System.out.println(code2);
 
-
-
+        byte[] bytes = new byte[]{
+                -28, -67, -96,
+                -24, -117, -91,
+                -27, -82, -119,
+                -27, -91, -67,
+                -17, -68, -116,
+                -28, -66, -65,
+                -26, -104, -81,
+                -26, -103, -76,
+                -27, -92, -87
+        };
+        // 猜猜输出什么
+        System.out.println(new String(bytes));
+        System.out.println(Arrays.toString(new String(bytes).getBytes()));
     }
 
 }

src/class43/ArrayListDemo1.java

@@ -0,0 +1,27 @@
+package class43;
+
+import java.util.ArrayList;
+
+public class ArrayListDemo1 {
+    public static void main(String[] args) {
+        ArrayList<String> list=new ArrayList<>();//泛型约束传入类型
+        list.add("hello");
+        list.add("world");
+        list.add("java");
+        list.add("heima");
+        System.out.println(list);
+
+        System.out.println("========================================");
+        for(String s: list){
+            System.out.println(s);
+        }
+        System.out.println("========================================");
+        System.out.println(list.remove(2));
+        System.out.println(list);
+        System.out.println(list.remove("heima"));
+        System.out.println(list);
+
+        list.set(0,"hello world");
+        System.out.println(list);
+    }
+}