diff --git a/w8 b/w8
new file mode 100644
index 0000000..36639ed
--- /dev/null
+++ b/w8
@@ -0,0 +1,31 @@
+public class Pair<K, V> {
+    private K key;
+    private V value;
+
+    public Pair(K key, V value) {
+        this.key = key;
+        this.value = value;
+    }
+
+    public K getKey() { return key; }
+    public V getValue() { return value; }
+
+    // swap：交换后原key变value，原value变key，返回新Pair
+    public Pair<V, K> swap() {
+        return new Pair<>(value, key);
+    }
+}
+
+
+import java.util.concurrent.ConcurrentHashMap;
+
+public class Cache<K, V> {
+    private final ConcurrentHashMap<K, V> cache = new ConcurrentHashMap<>();
+
+    public void put(K key, V value) { cache.put(key, value); }
+    public V get(K key) { return cache.get(key); }
+    public V remove(K key) { return cache.remove(key); }
+    public void clear() { cache.clear(); }
+    public int size() { return cache.size(); }
+    public boolean containsKey(K key) { return cache.containsKey(key); }
+}
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