[英]Display tree hierarchy with their values in Java
I have to create a tree structure with a parent node having many children, and each child can also have their children. 我必须创建一个具有许多子节点的父节点的树结构,并且每个子节点也可以具有其子节点。 Each node will be identified by their unique id and name.
每个节点将通过其唯一的ID和名称进行标识。
So when I enter any id from the hierarchy, all node-ids and their child node-ids with their names should get printed. 因此,当我输入层次结构中的任何ID时,应打印所有节点ID及其名称的子节点ID。 How can I achieve this(any sample code would help) and which collection should be used from collection framework or do I have to use plain data structures in Java?
如何实现这一点(任何示例代码都会有帮助)以及应从集合框架中使用哪个集合,还是必须在Java中使用纯数据结构?
One possible way is to create your own tree structure (node with children) and wrap it into another structure that tracks nodes' ids. 一种可能的方法是创建自己的树结构(带有子节点的节点)并将其包装到另一个跟踪节点ID的结构中。 Something like that:
像这样:
public class Tree<I, A> {
private final HashMap<I, Node<I, A>> map = new HashMap<>();
private final Node<I, A> root;
public Tree(I id, A value) {
root = new Node<>(id, value);
map.put(id, root);
}
public void addChild(I parentId, I id, A value) {
Node<I, A> parent = map.get(parentId);
Node<I, A> child = new Node<>(id, value);
parent.children.add(child);
map.put(id, child);
}
public A getById(I id) {
return map.get(id).value;
}
public String subtreeToString(I id) {
return map.get(id).toString();
}
private static class Node<I, A> {
private final I id;
private final A value;
private final ArrayList<Node<I, A>> children = new ArrayList<>();
private Node(I id, A value) {
this.id = id;
this.value = value;
}
private void print(int depth, PrintWriter pw) {
for (int i = 0; i < depth; i++) {
pw.print("\t");
}
pw.println("[" + id + ", " + value + "]");
for (Node<I, A> child : children) {
child.print(depth + 1, pw);
}
}
@Override
public String toString() {
StringWriter writer = new StringWriter();
print(0, new PrintWriter(writer));
return writer.toString();
}
}
}
Usage: 用法:
Tree<Integer, String> tree = new Tree<>(1, "Bob");
tree.addChild(1, 2, "John");
tree.addChild(1, 3, "James");
tree.addChild(2, 4, "David");
tree.addChild(2, 5, "Alice");
System.out.println(tree.subtreeToString(1));
System.out.println(tree.subtreeToString(2));
Output: 输出:
[1, Bob]
[2, John]
[4, David]
[5, Alice]
[3, James]
[2, John]
[4, David]
[5, Alice]
您将必须制作自己的树结构,并且在打印时,只需在父节点上调用toString(),然后从该节点上在子节点上调用toString()等。
There might be some structure ready for the task, but on the other hand: this task is very straightforward to do yourself – just do a recursive in-order walk down the tree: 可能已经为该任务准备了一些结构,但另一方面:此任务很容易自己完成–只需按顺序递归地沿树走即可:
Good luck. 祝好运。
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