根据VasyaNovikov的回答。改进了一些Java魔术:泛型和函数接口。

/**
 * Print a tree structure in a pretty ASCII fromat.
 * @param prefix Currnet previx. Use "" in initial call!
 * @param node The current node. Pass the root node of your tree in initial call.
 * @param getChildrenFunc A {@link Function} that returns the children of a given node.
 * @param isTail Is node the last of its sibblings. Use true in initial call. (This is needed for pretty printing.)
 * @param <T> The type of your nodes. Anything that has a toString can be used.
 */
private <T> void printTreeRec(String prefix, T node, Function<T, List<T>> getChildrenFunc, boolean isTail) {
    String nodeName = node.toString();
    String nodeConnection = isTail ? "└── " : "├── ";
    log.debug(prefix + nodeConnection + nodeName);
    List<T> children = getChildrenFunc.apply(node);
    for (int i = 0; i < children.size(); i++) {
        String newPrefix = prefix + (isTail ? "    " : "│   ");
        printTreeRec(newPrefix, children.get(i), getChildrenFunc, i == children.size()-1);
    }
}

初始调用示例:

Function<ChecksumModel, List<ChecksumModel>> getChildrenFunc = node -> getChildrenOf(node)
printTreeRec("", rootNode, getChildrenFunc, true);

将输出如下内容

└── rootNode
    ├── childNode1
    ├── childNode2
    │   ├── childNode2.1
    │   ├── childNode2.2
    │   └── childNode2.3
    ├── childNode3
    └── childNode4

我需要在我的一个项目中打印一个二叉树，为此我准备了一个java类TreePrinter，其中一个示例输出是:

                [+]
               /   \
              /     \
             /       \
            /         \
           /           \
        [*]             \
       /   \             [-]
[speed]     [2]         /   \
                    [45]     [12]

下面是TreePrinter类和TextNode类的代码。为了打印任何树，你可以用TextNode类创建一个等效的树。

import java.util.ArrayList;

public class TreePrinter {

    public TreePrinter(){
    }

    public static String TreeString(TextNode root){
        ArrayList layers = new ArrayList();
        ArrayList bottom = new ArrayList();

        FillBottom(bottom, root);  DrawEdges(root);

        int height = GetHeight(root);
        for(int i = 0; i  s.length()) min = s.length();

            if(!n.isEdge) s += "[";
            s += n.text;
            if(!n.isEdge) s += "]";

            layers.set(n.depth, s);
        }

        StringBuilder sb = new StringBuilder();

        for(int i = 0; i  temp = new ArrayList();

            for(int i = 0; i  0) temp.get(i-1).left = x;
                temp.add(x);
            }

            temp.get(count-1).left = n.left;
            n.left.depth = temp.get(count-1).depth+1;
            n.left = temp.get(0);

            DrawEdges(temp.get(count-1).left);
        }
        if(n.right != null){
            int count = n.right.x - (n.x + n.text.length() + 2);
            ArrayList temp = new ArrayList();

            for(int i = 0; i  0) temp.get(i-1).right = x;
                temp.add(x);
            }

            temp.get(count-1).right = n.right;
            n.right.depth = temp.get(count-1).depth+1;
            n.right = temp.get(0);  

            DrawEdges(temp.get(count-1).right);
        }
    }

    private static void FillBottom(ArrayList bottom, TextNode n){
        if(n == null) return;

        FillBottom(bottom, n.left);

        if(!bottom.isEmpty()){            
            int i = bottom.size()-1;
            while(bottom.get(i).isEdge) i--;
            TextNode last = bottom.get(i);

            if(!n.isEdge) n.x = last.x + last.text.length() + 3;
        }
        bottom.add(n);
        FillBottom(bottom, n.right);
    }

    private static boolean isLeaf(TextNode n){
        return (n.left == null && n.right == null);
    }

    private static int GetHeight(TextNode n){
        if(n == null) return 0;

        int l = GetHeight(n.left);
        int r = GetHeight(n.right);

        return Math.max(l, r) + 1;
    }
}


class TextNode {
    public String text;
    public TextNode parent, left, right;
    public boolean isEdge;
    public int x, depth;

    public TextNode(String text){
        this.text = text;
        parent = null; left = null; right = null;
        isEdge = false;
        x = 0; depth = 0;
    }
}

最后，这里是一个打印给定样本的测试类:

public class Test {

    public static void main(String[] args){
        TextNode root = new TextNode("+");
        root.left = new TextNode("*");            root.left.parent = root;
        root.right = new TextNode("-");           root.right.parent = root;
        root.left.left = new TextNode("speed");   root.left.left.parent = root.left;
        root.left.right = new TextNode("2");      root.left.right.parent = root.left;
        root.right.left = new TextNode("45");     root.right.left.parent = root.right;
        root.right.right = new TextNode("12");    root.right.right.parent = root.right;

        System.out.println(TreePrinter.TreeString(root));
    }
}

我已经创建了简单的二叉树打印机。您可以随心所欲地使用和修改它，但无论如何它都没有优化。我认为这里有很多东西可以改进;)

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;

public class BTreePrinterTest {

    private static Node<Integer> test1() {
        Node<Integer> root = new Node<Integer>(2);
        Node<Integer> n11 = new Node<Integer>(7);
        Node<Integer> n12 = new Node<Integer>(5);
        Node<Integer> n21 = new Node<Integer>(2);
        Node<Integer> n22 = new Node<Integer>(6);
        Node<Integer> n23 = new Node<Integer>(3);
        Node<Integer> n24 = new Node<Integer>(6);
        Node<Integer> n31 = new Node<Integer>(5);
        Node<Integer> n32 = new Node<Integer>(8);
        Node<Integer> n33 = new Node<Integer>(4);
        Node<Integer> n34 = new Node<Integer>(5);
        Node<Integer> n35 = new Node<Integer>(8);
        Node<Integer> n36 = new Node<Integer>(4);
        Node<Integer> n37 = new Node<Integer>(5);
        Node<Integer> n38 = new Node<Integer>(8);

        root.left = n11;
        root.right = n12;

        n11.left = n21;
        n11.right = n22;
        n12.left = n23;
        n12.right = n24;

        n21.left = n31;
        n21.right = n32;
        n22.left = n33;
        n22.right = n34;
        n23.left = n35;
        n23.right = n36;
        n24.left = n37;
        n24.right = n38;

        return root;
    }

    private static Node<Integer> test2() {
        Node<Integer> root = new Node<Integer>(2);
        Node<Integer> n11 = new Node<Integer>(7);
        Node<Integer> n12 = new Node<Integer>(5);
        Node<Integer> n21 = new Node<Integer>(2);
        Node<Integer> n22 = new Node<Integer>(6);
        Node<Integer> n23 = new Node<Integer>(9);
        Node<Integer> n31 = new Node<Integer>(5);
        Node<Integer> n32 = new Node<Integer>(8);
        Node<Integer> n33 = new Node<Integer>(4);

        root.left = n11;
        root.right = n12;

        n11.left = n21;
        n11.right = n22;

        n12.right = n23;
        n22.left = n31;
        n22.right = n32;

        n23.left = n33;

        return root;
    }

    public static void main(String[] args) {

        BTreePrinter.printNode(test1());
        BTreePrinter.printNode(test2());

    }
}

class Node<T extends Comparable<?>> {
    Node<T> left, right;
    T data;

    public Node(T data) {
        this.data = data;
    }
}

class BTreePrinter {

    public static <T extends Comparable<?>> void printNode(Node<T> root) {
        int maxLevel = BTreePrinter.maxLevel(root);

        printNodeInternal(Collections.singletonList(root), 1, maxLevel);
    }

    private static <T extends Comparable<?>> void printNodeInternal(List<Node<T>> nodes, int level, int maxLevel) {
        if (nodes.isEmpty() || BTreePrinter.isAllElementsNull(nodes))
            return;

        int floor = maxLevel - level;
        int endgeLines = (int) Math.pow(2, (Math.max(floor - 1, 0)));
        int firstSpaces = (int) Math.pow(2, (floor)) - 1;
        int betweenSpaces = (int) Math.pow(2, (floor + 1)) - 1;

        BTreePrinter.printWhitespaces(firstSpaces);

        List<Node<T>> newNodes = new ArrayList<Node<T>>();
        for (Node<T> node : nodes) {
            if (node != null) {
                System.out.print(node.data);
                newNodes.add(node.left);
                newNodes.add(node.right);
            } else {
                newNodes.add(null);
                newNodes.add(null);
                System.out.print(" ");
            }

            BTreePrinter.printWhitespaces(betweenSpaces);
        }
        System.out.println("");

        for (int i = 1; i <= endgeLines; i++) {
            for (int j = 0; j < nodes.size(); j++) {
                BTreePrinter.printWhitespaces(firstSpaces - i);
                if (nodes.get(j) == null) {
                    BTreePrinter.printWhitespaces(endgeLines + endgeLines + i + 1);
                    continue;
                }

                if (nodes.get(j).left != null)
                    System.out.print("/");
                else
                    BTreePrinter.printWhitespaces(1);

                BTreePrinter.printWhitespaces(i + i - 1);

                if (nodes.get(j).right != null)
                    System.out.print("\\");
                else
                    BTreePrinter.printWhitespaces(1);

                BTreePrinter.printWhitespaces(endgeLines + endgeLines - i);
            }

            System.out.println("");
        }

        printNodeInternal(newNodes, level + 1, maxLevel);
    }

    private static void printWhitespaces(int count) {
        for (int i = 0; i < count; i++)
            System.out.print(" ");
    }

    private static <T extends Comparable<?>> int maxLevel(Node<T> node) {
        if (node == null)
            return 0;

        return Math.max(BTreePrinter.maxLevel(node.left), BTreePrinter.maxLevel(node.right)) + 1;
    }

    private static <T> boolean isAllElementsNull(List<T> list) {
        for (Object object : list) {
            if (object != null)
                return false;
        }

        return true;
    }

}

输出1:

         2               
        / \       
       /   \      
      /     \     
     /       \    
     7       5       
    / \     / \   
   /   \   /   \  
   2   6   3   6   
  / \ / \ / \ / \ 
  5 8 4 5 8 4 5 8 

输出2:

       2               
      / \       
     /   \      
    /     \     
   /       \    
   7       5       
  / \       \   
 /   \       \  
 2   6       9   
    / \     /   
    5 8     4   

public void printPreety() {
    List<TreeNode> list = new ArrayList<TreeNode>();
    list.add(head);
    printTree(list, getHeight(head));
}

public int getHeight(TreeNode head) {

    if (head == null) {
        return 0;
    } else {
        return 1 + Math.max(getHeight(head.left), getHeight(head.right));
    }
}

/**
 * pass head node in list and height of the tree 
 * 
 * @param levelNodes
 * @param level
 */
private void printTree(List<TreeNode> levelNodes, int level) {

    List<TreeNode> nodes = new ArrayList<TreeNode>();

    //indentation for first node in given level
    printIndentForLevel(level);

    for (TreeNode treeNode : levelNodes) {

        //print node data
        System.out.print(treeNode == null?" ":treeNode.data);

        //spacing between nodes
        printSpacingBetweenNodes(level);

        //if its not a leaf node
        if(level>1){
            nodes.add(treeNode == null? null:treeNode.left);
            nodes.add(treeNode == null? null:treeNode.right);
        }
    }
    System.out.println();

    if(level>1){        
        printTree(nodes, level-1);
    }
}

private void printIndentForLevel(int level){
    for (int i = (int) (Math.pow(2,level-1)); i >0; i--) {
        System.out.print(" ");
    }
}

private void printSpacingBetweenNodes(int level){
    //spacing between nodes
    for (int i = (int) ((Math.pow(2,level-1))*2)-1; i >0; i--) {
        System.out.print(" ");
    }
}


Prints Tree in following format:
                4                               
        3               7               
    1               5       8       
      2                       10   
                             9   

下面是可视化树的另一种方法:将节点保存为xml文件，然后让浏览器显示层次结构:

class treeNode{
    int key;
    treeNode left;
    treeNode right;

    public treeNode(int key){
        this.key = key;
        left = right = null;
    }

    public void printNode(StringBuilder output, String dir){
        output.append("<node key='" + key + "' dir='" + dir + "'>");
        if(left != null)
            left.printNode(output, "l");
        if(right != null)
            right.printNode(output, "r");
        output.append("</node>");
    }
}

class tree{
    private treeNode treeRoot;

    public tree(int key){
        treeRoot = new treeNode(key);
    }

    public void insert(int key){
        insert(treeRoot, key);
    }

    private treeNode insert(treeNode root, int key){
        if(root == null){
            treeNode child = new treeNode(key);
            return child;
        }

        if(key < root.key)
            root.left = insert(root.left, key);
        else if(key > root.key)
            root.right = insert(root.right, key);

        return root;
    }

    public void saveTreeAsXml(){
        StringBuilder strOutput = new StringBuilder();
        strOutput.append("<?xml version=\"1.0\" encoding=\"UTF-8\"?>");
        treeRoot.printNode(strOutput, "root");
        try {
            PrintWriter writer = new PrintWriter("C:/tree.xml", "UTF-8");
            writer.write(strOutput.toString());
            writer.close();
        }
        catch (FileNotFoundException e){

        }
        catch(UnsupportedEncodingException e){

        }
    }
}

下面是测试它的代码:

    tree t = new tree(1);
    t.insert(10);
    t.insert(5);
    t.insert(4);
    t.insert(20);
    t.insert(40);
    t.insert(30);
    t.insert(80);
    t.insert(60);
    t.insert(50);

    t.saveTreeAsXml();

输出如下所示:

迈克尔。克鲁兹曼，我不得不说，这人不错。这很有用。

然而，上面的方法只适用于个位数:如果您要使用多个数字，结构将会错位，因为您使用的是空格而不是制表符。

至于我后来的代码，我需要更多的数字，所以我自己编写了一个程序。

它现在有一些bug，现在我感觉很懒去纠正它们，但它打印得非常漂亮，节点可以接受更大数量的数字。

这棵树不会像问题提到的那样，但它旋转了270度:)

public static void printBinaryTree(TreeNode root, int level){
    if(root==null)
         return;
    printBinaryTree(root.right, level+1);
    if(level!=0){
        for(int i=0;i<level-1;i++)
            System.out.print("|\t");
        System.out.println("|-------"+root.val);
    }
    else
        System.out.println(root.val);
    printBinaryTree(root.left, level+1);
}    

将此函数与您自己指定的TreeNode一起放置，并保持初始级别为0，并享受!

以下是一些输出示例:

|       |       |-------11
|       |-------10
|       |       |-------9
|-------8
|       |       |-------7
|       |-------6
|       |       |-------5
4
|       |-------3
|-------2
|       |-------1


|       |       |       |-------10
|       |       |-------9
|       |-------8
|       |       |-------7
|-------6
|       |-------5
4
|       |-------3
|-------2
|       |-------1

唯一的问题是延伸的分支;我会尽快解决这个问题，但在此之前你也可以使用它。