练习

src/main/java/com/github/hcsp/polymorphism/User.java

@@ -1,13 +1,19 @@
 package com.github.hcsp.polymorphism;
 
+import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.List;
+import java.util.function.Consumer;
 
 public class User {
-    /** 用户ID，数据库主键，全局唯一 */
+    /**
+     * 用户ID，数据库主键，全局唯一
+     */
     private final Integer id;
 
-    /** 用户名 */
+    /**
+     * 用户名
+     */
     private final String name;
 
     public User(Integer id, String name) {
@@ -31,6 +37,19 @@ public static List<String> collectNames(List<User> users) {
         return collector.getNames();
     }
 
+    private static class NameCollector implements Consumer<User> {
+        private final List<String> names = new ArrayList<>();
+
+        @Override
+        public void accept(User user) {
+            names.add(user.getName());
+        }
+
+        public List<String> getNames() {
+            return names;
+        }
+    }
+
     public static void main(String[] args) {
         List<User> users = Arrays.asList(new User(1, "a"), new User(2, "b"));
         System.out.println(collectNames(users));