diff --git a/w8/Pair.java b/w8/Pair.java
new file mode 100644
index 0000000..fe86dad
--- /dev/null
+++ b/w8/Pair.java
@@ -0,0 +1,111 @@
+import java.lang.reflect.ParameterizedType;
+import java.lang.reflect.Type;
+import java.util.HashMap;
+import java.util.Map;
+
+public class Pair<K, V> {
+    private K first;
+    private V second;
+
+    public Pair(K first, V second) {
+        this.first = first;
+        this.second = second;
+    }
+
+    public K getFirst() {
+        return first;
+    }
+
+    public void setFirst(K first) {
+        this.first = first;
+    }
+
+    public V getSecond() {
+        return second;
+    }
+
+    public void setSecond(V second) {
+        this.second = second;
+    }
+
+    /**
+     * 安全地交换 Pair 中的两个元素。
+     * 注意：这将创建一个新的 Pair 对象并返回，而不是修改原对象。
+     */
+    public Pair<V, K> swapped() {
+        return new Pair<>(this.second, this.first);
+    }
+
+    @Override
+    public String toString() {
+        return "Pair{first=" + first + ", second=" + second + '}';
+    }
+
+    public static class Cache<K, V> {
+        private final Map<K, V> cache = new HashMap<>();
+
+        public void put(K key, V value) {
+            cache.put(key, value);
+        }
+
+        public V get(K key) {
+            return cache.get(key);
+        }
+
+        public boolean containsKey(K key) {
+            return cache.containsKey(key);
+        }
+
+        public void remove(K key) {
+            cache.remove(key);
+        }
+
+        public int size() {
+            return cache.size();
+        }
+
+        // 为了能够通过反射获取泛型信息，需要让子类继承它
+        public Class<?> getKeyType() {
+            return getGenericType(0);
+        }
+
+        public Class<?> getValueType() {
+            return getGenericType(1);
+        }
+
+        private Class<?> getGenericType(int index) {
+            Type genericSuperclass = this.getClass().getGenericSuperclass();
+            if (genericSuperclass instanceof ParameterizedType) {
+                ParameterizedType parameterizedType = (ParameterizedType) genericSuperclass;
+                Type[] actualTypeArguments = parameterizedType.getActualTypeArguments();
+                if (index >= 0 && index < actualTypeArguments.length) {
+                    Type type = actualTypeArguments[index];
+                    if (type instanceof Class) {
+                        return (Class<?>) type;
+                    }
+                }
+            }
+            return Object.class;
+        }
+    }
+
+    public static void main(String[] args) {
+        // 演示 Pair 的用法
+        Pair<String, Integer> pair = new Pair<>("Hello", 100);
+        System.out.println("Original Pair: " + pair);
+        Pair<Integer, String> swappedPair = pair.swapped();
+        System.out.println("Swapped Pair: " + swappedPair);
+
+        // 演示 Cache 的用法和泛型类型获取
+        // 必须创建一个匿名子类才能保留泛型信息供反射使用
+        Cache<String, Integer> stringIntCache = new Cache<String, Integer>() {};
+        stringIntCache.put("answer", 42);
+        stringIntCache.put("year", 2024);
+
+        System.out.println("\n--- Cache Demo ---");
+        System.out.println("Key type: " + stringIntCache.getKeyType().getSimpleName());
+        System.out.println("Value type: " + stringIntCache.getValueType().getSimpleName());
+        System.out.println("Size: " + stringIntCache.size());
+        System.out.println("Value for 'answer': " + stringIntCache.get("answer"));
+    }
+}
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