java构建树(tree)型结构，只循环一次非递归

只循环一次构建树形结构，可以直接加入工具类使用，代码如下

public static <T, I> List<T> lambdaGenerateTree(List<T> allTreeNode,
                                                    Callback<T, I> getIdCallback,
                                                    Callback<T, I> getParentIdCallback,
                                                    BiConsumer<T, List<T>> setChildrenListCallback,
                                                    I topParentId) {
        List<T> topTreeNodeList = new ArrayList<>();
        Map<I, List<T>> allTreeNodeChildrenMap = new HashMap<>(allTreeNode.size());
 
        allTreeNode.forEach(treeNode -> {
            if (allTreeNodeChildrenMap.containsKey(getIdCallback.call(treeNode))) {
                // 该节点children已始化时建立引用
                setChildrenListCallback.accept(treeNode, allTreeNodeChildrenMap.get(getIdCallback.call(treeNode)));
            } else {
                // 该节点children还未初始化时进行初始化并建立引用
                List<T> childrenList = new ArrayList<>();
                setChildrenListCallback.accept(treeNode, childrenList);
                allTreeNodeChildrenMap.put(getIdCallback.call(treeNode), childrenList);
            }
            if (getParentIdCallback == topParentId || getParentIdCallback.call(treeNode).equals(topParentId)) {
                // top节点将节点放入top节点的List中
                topTreeNodeList.add(treeNode);
            } else {
                // 叶子节点
                if (allTreeNodeChildrenMap.containsKey(getParentIdCallback.call(treeNode))) {
                    // 当父节点的子集实例存在，则把自个儿丢进去
                    allTreeNodeChildrenMap.get(getParentIdCallback.call(treeNode)).add(treeNode);
                } else {
                    // 当父节点的子集实例不存在，提前实例化它，并把自个儿丢进去
                    List<T> parentChildrenList = new ArrayList<>();
                    parentChildrenList.add(treeNode);
                    allTreeNodeChildrenMap.put(getParentIdCallback.call(treeNode), parentChildrenList);
                }
            }
        });
        return topTreeNodeList;
    }

代码大致思路如下：

1.遍历每个节点时首先进行children节点list的关联，如果该节点的children节点还未初始化，则初始化并建立关联

2.根节点将自己放入根节点list中作为返回结果

3.叶子节点将自己放入父节点children list中，如果还未实例化则提前实例化它

使用方式如下：

TreeUtil.lambdaGenerateTree(treeNodeList,
                TreeNode::getId,
                TreeNode::getParentId,
                TreeNode::setChildren,
                -1L)

转载自:https://blog.csdn.net/qq_37720936/article/details/126409247