add week8 code

w8/集合键值转换.java

@@ -0,0 +1,23 @@
+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;
+    }
+    public void setKey(K key){
+        this.key=key;
+    }
+    public void setValue(V value){
+        this.value=value;
+    }
+    public static <K,V> Pair<V,K> swap(Pair<K,V> pair){
+        return new Pair<>(pair.getValue(), pair.getKey());
+    }
+}