java list 转树 tree 的三种写法

╰+攻爆jí腚メ 2022-05-16 05:41 223阅读 0赞

package com.lzk;
    
    import java.util.List;
    
    public class TreeNode {
        private String id;
    
        private String name;
    
        private String pid;
    
        private List<TreeNode> childrens;
    
        public TreeNode(String id,String name,String pid){
            this.id = id;
            this.name = name;
            this.pid = pid;
        }
    
        public String getId() {
            return id;
        }
    
        public void setId(String id) {
            this.id = id;
        }
    
        public String getName() {
            return name;
        }
    
        public void setName(String name) {
            this.name = name;
        }
    
        public String getPid() {
            return pid;
        }
    
        public void setPid(String pid) {
            this.pid = pid;
        }
    
        public List<TreeNode> getChildrens() {
            return childrens;
        }
    
        public void setChildrens(List<TreeNode> childrens) {
            this.childrens = childrens;
        }
    
        @Override
        public String toString() {
            return "TreeNode{" +
                    "id='" + id + '\'' +
                    ", name='" + name + '\'' +
                    ", pid='" + pid + '\'' +
                    ", childrens=" + childrens +
                    '}';
        }
    }

package com.lzk;
    
    import java.util.ArrayList;
    import java.util.List;
    
    public class TreeBuild {
    
        /**
         * 方式一：使用两层循环实现
         * @param treeList
         * @return
         */
        public static List<TreeNode> toTree01(List<TreeNode> treeList,String pid) {
            List<TreeNode> retList = new ArrayList<TreeNode>();
            for (TreeNode parent : treeList) {
                if (pid.equals(parent.getPid())) {
                    retList.add(parent);
                }
                for (TreeNode child : treeList) {
                    if (child.getPid() == parent.getId()) {
                        if (parent.getChildrens() == null) {
                            parent.setChildrens(new ArrayList<TreeNode>());
                        }
                        parent.getChildrens().add(child);
                    }
                }
            }
            return retList;
        }
    
        /**
         * 方式二：使用递归实现
         * @param treeList
         * @return
        **/
        public static List<TreeNode> toTree02(List<TreeNode> treeList,String pid) {
            List<TreeNode> retList = new ArrayList<TreeNode>();
            for (TreeNode parent : treeList) {
                if (pid.equals(parent.getPid())) {
                    retList.add(findChildren(parent, treeList));
                }
            }
            return retList;
        }
    
        /*
        * 查询父节点下的所有子节点
        * */
        private static TreeNode findChildren(TreeNode parent, List<TreeNode> treeList) {
            for (TreeNode child : treeList) {
                if (parent.getId().equals(child.getPid())) {
                    if (parent.getChildrens() == null) {
                        parent.setChildrens(new ArrayList<TreeNode>());
                    }
                    parent.getChildrens().add(findChildren(child, treeList));
                }
            }
            return parent;
        }
    
        /**
         *方法三
         * @param list
         * @return
         */
        public static List<TreeNode> toTree03(List<TreeNode> list,String pid) {
            List<TreeNode> treeList = new ArrayList<TreeNode>();
            for (TreeNode tree : list) {
                if(tree.getPid().equals(pid)){
                    treeList.add(tree);
                }
            }
            for (TreeNode tree : list) {
                toTreeChildren(treeList,tree);
            }
            return treeList;
        }
    
        public static void toTreeChildren(List<TreeNode> treeList, TreeNode tree) {
            for (TreeNode node : treeList) {
                if(tree.getPid() == node.getId()){
                    if(node.getChildrens() == null){
                        node.setChildrens(new ArrayList<TreeNode>());
                    }
                    node.getChildrens().add(tree);
                }
                if(node.getChildrens() != null){
                    toTreeChildren(node.getChildrens(),tree);
                }
            }
        }
    }

package com.lzk;
    
    import java.util.ArrayList;
    import java.util.List;
    
    public class test {
        public static void main(String[] args) {
            List<TreeNode> list = new ArrayList<TreeNode>();
            list.add(new TreeNode("1", "顶层节点1", "0"));
            list.add(new TreeNode("2", "顶层节点2", "0"));
            list.add(new TreeNode("3", "顶层节点3", "0"));
            list.add(new TreeNode("4", "二级节点4", "1"));
            list.add(new TreeNode("5", "二级节点5", "2"));
            list.add(new TreeNode("6", "二级节点6", "3"));
            list.add(new TreeNode("7", "三级节点7", "4"));
            list.add(new TreeNode("8", "三级节点8", "4"));
            list.add(new TreeNode("9", "三级节点9", "5"));
    //        List<TreeNode> list1 = TreeBuild.toTree02(list,"0");
    //        System.out.println(list1);
            List<TreeNode> list2 = TreeBuild.toTree03(list,"0");
            System.out.println(list2);
        }
    }