Add Java codes, and license.

codes/java/include/ListNode.java

@@ -0,0 +1,41 @@
+package include;
+
+/**
+ * Definition for a singly-linked list node
+ */
+public class ListNode {
+    public int val;
+    public ListNode next;
+
+    public ListNode(int x) {
+        val = x;
+    }
+    
+    /**
+     * Generate a linked list with an array
+     * @param arr
+     * @return
+     */
+    public static ListNode arrToLinkedList(int[] arr) {
+        ListNode dum = new ListNode(0);
+        ListNode head = dum;
+        for (int val : arr) {
+            head.next = new ListNode(val);
+            head = head.next;
+        }
+        return dum.next;
+    }
+
+    /**
+     * Get a list node with specific value from a linked list
+     * @param head
+     * @param val
+     * @return
+     */
+    public static ListNode getListNode(ListNode head, int val) {
+        while (head != null && head.val != val) {
+            head = head.next;
+        }
+        return head;
+    }
+}