从上到下打印二叉树

import java.util.ArrayList;import java.util.LinkedList;import java.util.Queue;/** *  思路: 因为要按照顺序打印二叉树，所以在我们输出 *  根节点的值后，需要把当前结点的左右子树保存到队列中。 *  之后再从队列的头中取出结点，一直循环直到全部输出所有结点为止 * *  采用队列是因为队列是先进先出的结构 */public class PrintTtoB_BiTree {    private static Queue<BiTree> queue = new LinkedList<>();    private static int a[] = {1,2,0,4,5,0,0,0,3,6,0,0,0};    static int length = 0;    public static BiTree createBiTree1(BiTree T){        if (length == a.length)            return null;        int value = a[length++] ;        if(value == 0)                T = null;        else{            T = new BiTree();            T.setValue(value);            T.setmLeftChild(createBiTree1(T.mLeftChild));            T.setmRightChild(createBiTree1(T.mRightChild));        }        return T;    }    public static BiTree createBiTree(BiTree root) {        if (length < a.length) {            int value = a[length++];            if (value == 0) {                root = null;            } else {                BiTree lchild = new BiTree();                BiTree rchild = new BiTree();                root.value = value;                root.mLeftChild = createBiTree(lchild);                root.mRightChild = createBiTree(rchild);            }        }        return root;    }    public static void PrintFromToptoBottom(BiTree biTree){        if (biTree == null)                return;        queue.add(biTree);        while (queue.size() > 0){            System.out.println(queue.peek().value);            biTree = queue.peek();            queue.poll();            if(biTree.getmLeftChild() != null)                queue.add(biTree.getmLeftChild());            if(biTree.getmRightChild() != null)                queue.add(biTree.getmRightChild());        }    }    public static void main(String[] args){        BiTree biTree = new BiTree();        createBiTree(biTree);        PrintFromToptoBottom(biTree);    }    static class BiTree{        private int value;        private BiTree mLeftChild;        private BiTree mRightChild;        public int getValue() {            return value;        }        public void setValue(int value) {            this.value = value;        }        public BiTree getmLeftChild() {            return mLeftChild;        }        public void setmLeftChild(BiTree mLeftChild) {            this.mLeftChild = mLeftChild;        }        public BiTree getmRightChild() {            return mRightChild;        }        public void setmRightChild(BiTree mRightChild) {            this.mRightChild = mRightChild;        }    }}