将父/子关系的java arrayList转换为树？

本文介绍了将父/子关系的java arrayList转换为树？的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！ 问题描述 我有一堆父/子对，我想尽可能转变为分层树结构。例如，这些可能是配对：I have a bunch of parent/child pairs, that I'd like to turn into hierarchical tree structures as possible. So for example, these could be the pairings:Child : Parent H : Ga F : G G : D E : D A : E B : C C : E D : NULL Z : Y Y : X X: NULL哪些需要转换为（ a）层次结构树：Which needs to be transformed into (a) heirarchical tree(s): D ├── E │ ├── A │ │ └── B │ └── C └── G | ├── F | └── H | X | └── Y | └──Z如何在Java中使用包含子节点的arrayList =>父对，到那样一棵树？How, in Java, would I go from an arrayList containing child=>parent pairs, to a Tree like that one?我需要这个操作的输出是arrayList包含两个元素D和X 依次每一个有孩子的列表，其中还包含一个孩子的列表等等i need the output of this operation is arrayList contains two elements D and Xin turn each one have list of its children which in turn also contains a list of children and so onpublic class MegaMenuDTO { private String Id; private String name; private String parentId; private List<MegaMenuDTO> childrenItems=new ArrayList<MegaMenuDTO>(); public String getId() { return Id; } public void setId(String id) { Id = id; } public String getName() { return name; } public void setName(String name) { this.name = name; } public String getParentId() { return parentId; } public void setParentId(String parentId) { this.parentId = parentId; } public List<MegaMenuDTO> getChildrenItems() { return childrenItems; } public void setChildrenItems(List<MegaMenuDTO> childrenItems) { this.childrenItems = childrenItems; }}我的第一次尝试是private void arrangeMegaMenuTree(MegaMenuDTO grandParent, MegaMenuDTO parent, List<MegaMenuDTO> children) { for (MegaMenuDTO child : children) { if (child.getParentId().equals(parent.getId())) { arrangeMegaMenuTree(parent, child, children); } } if (!grandParent.getId().equals(parent.getId())) { grandParent.getChildrenItems().add(parent); // children.remove(parent); }}再试一次private List<MegaMenuDTO> arrangeMegaMenuTree(MegaMenuDTOparent,List<MegaMenuDTO>menuItems) { for (MegaMenuDTO child : menuItems) { if (parent.getId().equals(child.getId())) { continue; } if (hasChildren(child, menuItems)) { parent.setChildrenItems(arrangeMegaMenuTree(child, menuItems .subList(menuItems.indexOf(child), menuItems.size()))); } else { List<MegaMenuDTO> tempList = new ArrayList<MegaMenuDTO>(); tempList.add(child); return tempList; } } return null;}private boolean hasChildren(MegaMenuDTO parent, List<MegaMenuDTO> children) { for (MegaMenuDTO child : children) { if (child.getParentId().equals(parent.getId())) { return true; } } return false;} 推荐答案这是一个替代解决方案在第一个答案和问题的更新...... :) Here is an alternative solution based on the first answer and the update of the question ... :) import java.util.ArrayList;import java.util.HashMap;import java.util.List;import java.util.Map;public class Main2 { public static void main(String[] args) { // input ArrayList<Pair> pairs = new ArrayList<Pair>(); pairs.add(new Pair( "H" , "G")); pairs.add(new Pair( "F" , "G")); pairs.add(new Pair( "G" , "D")); // ... // Arrange // String corresponds to the Id Map<String, MegaMenuDTO> hm = new HashMap<>(); // you are using MegaMenuDTO as Linked list with next and before link // populate a Map for(Pair p:pairs){ // ----- Child ----- MegaMenuDTO mmdChild ; if(hm.containsKey(p.getChildId())){ mmdChild = hm.get(p.getChildId()); } else{ mmdChild = new MegaMenuDTO(); hm.put(p.getChildId(),mmdChild); } mmdChild.setId(p.getChildId()); mmdChild.setParentId(p.getParentId()); // no need to set ChildrenItems list because the constructor created a new empty list // ------ Parent ---- MegaMenuDTO mmdParent ; if(hm.containsKey(p.getParentId())){ mmdParent = hm.get(p.getParentId()); } else{ mmdParent = new MegaMenuDTO(); hm.put(p.getParentId(),mmdParent); } mmdParent.setId(p.getParentId()); mmdParent.setParentId("null"); mmdParent.addChildrenItem(mmdChild); } // Get the root List<MegaMenuDTO> DX = new ArrayList<MegaMenuDTO>(); for(MegaMenuDTO mmd : hm.values()){ if(mmd.getParentId().equals("null")) DX.add(mmd); } // Print for(MegaMenuDTO mmd: DX){ System.out.println("DX contains "+DX.size()+" that are : "+ mmd); } }} 对类： Pair class :public class Pair { private String childId ; private String parentId; public Pair(String childId, String parentId) { this.childId = childId; this.parentId = parentId; } public String getChildId() { return childId; } public void setChildId(String childId) { this.childId = childId; } public String getParentId() { return parentId; } public void setParentId(String parentId) { this.parentId = parentId; }} MegaMenuDTO类已更新 MegaMenuDTO Class Updatedimport java.util.ArrayList;import java.util.List;public class MegaMenuDTO { private String Id; private String name; private String parentId; private List<MegaMenuDTO> childrenItems; public MegaMenuDTO() { this.Id = ""; this.name = ""; this.parentId = ""; this.childrenItems = new ArrayList<MegaMenuDTO>(); } public String getId() { return Id; } public void setId(String id) { Id = id; } public String getName() { return name; } public void setName(String name) { this.name = name; } public String getParentId() { return parentId; } public void setParentId(String parentId) { this.parentId = parentId; } public List<MegaMenuDTO> getChildrenItems() { return childrenItems; } public void setChildrenItems(List<MegaMenuDTO> childrenItems) { this.childrenItems = childrenItems; } public void addChildrenItem(MegaMenuDTO childrenItem){ if(!this.childrenItems.contains(childrenItem)) this.childrenItems.add(childrenItem); } @Override public String toString() { return "MegaMenuDTO [Id=" + Id + ", name=" + name + ", parentId=" + parentId + ", childrenItems=" + childrenItems + "]"; }} 这篇关于将父/子关系的java arrayList转换为树？的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！