サブツリーかどうかを判断する

2本の二叉木A,Bを入力し,BがAのサブ構造であるか否かを判断する.(ps:空の木は任意の木のサブ構造ではないと約束しました)

package dataStruts;

public class Tree {



    public static boolean isSubTree(TreeNode root,TreeNode root2){
        if(root2==null){
            return  true;
        }else if(root==null ){
            return  false;
        }else {
            if(root.val==root2.val){
                boolean left = isSubTree(root.left, root2.left);
                boolean right = isSubTree(root.right, root2.right);
                if(left&&right){
                    return true;
                }else {
                    return  false;
                }
            }else {
                return  false;
            }
        }
    }
    /**
     *   root2   root1   
     * @param root1
     * @param root2
     * @return
     */
    public static boolean HasSubtree(TreeNode root1,TreeNode root2) {
        boolean flag=false;
        if(root2==null || root1 ==null){
            return  false;
        }
        if(root1.val==root2.val){
            flag=isSubTree(root1,root2);
        }
        if(!flag){
            flag=HasSubtree(root1.left,root2);
        }
        if(!flag){
            flag=HasSubtree(root1.right,root2);
        }
        return flag ;

    }
    public static void main(String[] args) {
        TreeNode treeNode=new TreeNode(8);
        TreeNode treeNode1=new TreeNode(8);
        TreeNode treeNode2=new TreeNode(7);
        TreeNode treeNode3=new TreeNode(9);
        TreeNode treeNode4=new TreeNode(2);
        TreeNode treeNode5=new TreeNode(4);
        TreeNode treeNode6=new TreeNode(7);
        treeNode.left=treeNode1;
        treeNode.right=treeNode2;
        treeNode1.left=treeNode3;
        treeNode1.right=treeNode4;
        treeNode4.left=treeNode5;
        treeNode4.right=treeNode6;
        TreeNode treeNode7=new TreeNode(8);
        TreeNode treeNode8=new TreeNode(9);
        TreeNode treeNode9=new TreeNode(2);
        treeNode7.left=treeNode8;
        treeNode7.right=treeNode9;
        System.out.println(HasSubtree(treeNode,treeNode7));

    }
}