如何直观形象地树状打印一棵二叉树？

  1 BinarySearchTree<Integer> bst1 = bst(new Integer[]{
  2     7, 4, 9, 2, 5, 8, 11, 1, 3, 6, 10, 12
  3 });
  4 printer.treeln(bst1);
  5 /*
  6         7
  7       /     8     4       9
  9    / \     /  10   2   5   8   11
 11  / \   \     /   12 1   3   6   10  12
 13 */
 14 
 15 BinarySearchTree<Integer> bst2 = bst(new Integer[]{
 16     381, 12, 410, 9, 40, 394, 540, 
 17     35, 190, 476, 760, 146, 445,
 18     600, 800
 19 });
 20 printer.treeln(bst2);
 21 /*
 22         381
 23       /      24   12           410
 25  /  \         /    26 9    40     394   540
 27     /  \         /    28  35    190    476     760
 29       /       /      /    30     146     445    600   800
 31 */
 32 
 33 printer.treeln(bst(new Integer[]{
 34     30, 10, 60, 5, 20, 40, 80,
 35     15, 50, 70, 90
 36 }));
 37 /*
 38         30
 39      /       40   10          60
 41  /  \       /     42 5    20   40      80
 43     /       \    /   44   15        50  70  90
 45 */
 46 
 47 printer.treeln(new NodeOperation() {
 48     @Override
 49     public Object root() {
 50         return 8;
 51     }
 52     
 53     @Override
 54     public Object left(Object node) {
 55         if (node.equals(8)) return 3;
 56         if (node.equals(3)) return 1;
 57         if (node.equals(6)) return 4;
 58         if (node.equals(14)) return 13;
 59         return null;
 60     }
 61     
 62     @Override
 63     public Object right(Object node) {
 64         if (node.equals(8)) return 10;
 65         if (node.equals(10)) return 14;
 66         if (node.equals(3)) return 6;
 67         if (node.equals(6)) return 7;
 68         return null;
 69     }
 70 
 71     @Override
 72     public Object string(Object node) {
 73         return node;
 74     }
 75 });
 76 /*
 77           8
 78         /    79       3       10
 80      / \         81     1   6       14
 82        / \      /
 83       4   7   13
 84  */
 85 
 86 printer.treeln(new NodeOperation() {
 87     @Override
 88     public Object root() {
 89         return "Life";
 90     }
 91     
 92     @Override
 93     public Object left(Object node) {
 94         if (node.equals("Life")) return "Animal";
 95         if (node.equals("Person")) return "Man";
 96         if (node.equals("Animal")) return "Cat";
 97         if (node.equals("Dog")) return "Teddy";
 98         return null;
 99     }
100     
101     @Override
102     public Object right(Object node) {
103         if (node.equals("Life")) return "Person";
104         if (node.equals("Person")) return "Woman";
105         if (node.equals("Animal")) return "Dog";
106         if (node.equals("Dog")) return "SingleDog";
107         return null;
108     }
109 
110     @Override
111     public Object string(Object node) {
112         return node;
113     }
114 });
115 /*
116           Life
117         /      118   Animal        Person
119    /  \         /    120 Cat    Dog    Man    Woman
121      /     122  Teddy   SingleDog
123  */