Add Java codes, and license.

codes/java/include/TreeNode.java

@@ -0,0 +1,80 @@
+package include;
+
+import java.util.*;
+
+/**
+ * Definition for a binary tree node.
+ */
+public class TreeNode {
+    public int val;
+    public TreeNode left;
+    public TreeNode right;
+
+    public TreeNode(int x) {
+        val = x;
+    }
+
+    /**
+     * Generate a binary tree with an array
+     * @param arr
+     * @return
+     */
+    public static TreeNode arrToTree(Integer[] arr) {
+        TreeNode root = new TreeNode(arr[0]);
+        Queue<TreeNode> queue = new LinkedList<>() {{ add(root); }};
+        int i = 1;
+        while(!queue.isEmpty()) {
+            TreeNode node = queue.poll();
+            if(arr[i] != null) {
+                node.left = new TreeNode(arr[i]);
+                queue.add(node.left);
+            }
+            i++;
+            if(arr[i] != null) {
+                node.right = new TreeNode(arr[i]);
+                queue.add(node.right);
+            }
+            i++;
+        }
+        return root;
+    }
+
+    /**
+     * Serialize a binary tree to a list
+     * @param root
+     * @return
+     */
+    public static List<Integer> treeToList(TreeNode root) {
+        List<Integer> list = new ArrayList<>();
+        if(root == null) return list;
+        Queue<TreeNode> queue = new LinkedList<>() {{ add(root); }};
+        while(!queue.isEmpty()) {
+            TreeNode node = queue.poll();
+            if(node != null) {
+                list.add(node.val);
+                queue.add(node.left);
+                queue.add(node.right);
+            }
+            else {
+                list.add(null);
+            }
+        }
+        return list;
+    }
+    
+    /**
+     * Get a tree node with specific value in a binary tree
+     * @param root
+     * @param val
+     * @return
+     */
+    public static TreeNode getTreeNode(TreeNode root, int val) {
+        if (root == null)
+            return null;
+        if (root.val == val)
+            return root;
+        TreeNode left = getTreeNode(root.left, val);
+        TreeNode right = getTreeNode(root.right, val);
+        return left != null ? left : right;
+    }
+}