英文:
remove Subtree from tree in arrayList format
问题
以下是翻译好的内容：
public class GeneralTree<Tree>
{
private Tree data = null; // 创建一个树
private List<GeneralTree> children = new ArrayList<>(); // 创建一个ArrayList
private GeneralTree parent = null; // 创建一个父节点
public GeneralTree(Tree data) // 构造函数
{
this.data = data;
}
public void addChild(GeneralTree child) // 创建一个子节点方法
{
child.setParent(this);
this.children.add(child);
}
public void addChild(Tree data) // 创建一个将数据放入子节点的方法
{
GeneralTree<Tree> newChild = new GeneralTree<>(data);
this.addChild(newChild);
}
public void addChildren(List<GeneralTree> children) // 创建一个将子节点添加到父节点的方法
{
for(GeneralTree treeAdd: children)
{
treeAdd.setParent(this);
}
this.children.addAll(children);
}
public List<GeneralTree> getChildren() // 获取子节点
{
return this.children;
}
public Tree getData() // 获取子节点中的数据
{
return data;
}
public void setData(Tree data) // 设置子节点的数据
{
this.data = data;
}
public void setParent(GeneralTree parent) // 设置父节点
{
this.parent = parent;
}
public GeneralTree getParent() // 获取父节点
{
return this.parent;
}
public boolean isEmpty()
{
return this.children.isEmpty();
}
public List removeSubtree(GeneralTree child)
{
GeneralTree removed = removeTree(child);
return removed.children;
}
// ... 省略其他方法
}
public List removeSubtree(GeneralTree child)
{
GeneralTree removed = removeTree(child);
return removed.children;
}
public GeneralTree removeTree(GeneralTree remover)
{
return null;
}
public static void main(String[] args)
{
GeneralTree<String> root = new GeneralTree<>("Root"); // 创建一个根节点
GeneralTree<String> child1 = new GeneralTree<>("Child 1"); // 第一个子节点
child1.addChild("Grandchild 1"); // 第一个孙子节点
child1.addChild("Grandchild 2"); // 第二个孙子节点
GeneralTree<String> child2 = new GeneralTree<>("Child 2"); // 第二个子节点
child2.addChild("Grandchild 3"); // 第三个孙子节点
root.addChild(child1);
root.addChild(child2);
root.addChild("Child 3"); // 第三个子节点
root.addChildren(Arrays.asList(new GeneralTree<>("Child 4"), new GeneralTree<>("Child 5"), new GeneralTree<>("Child 6"))); // 添加第四、五、六个子节点
System.out.println(root.isEmpty()? "Empty": "Not Empty");
root.removeSubtree(child1);
for(GeneralTree node: root.getChildren()) // 获取并打印根节点下的子节点
{
System.out.println(node.getData()); // 获取数据
}
}
}
关于您的问题，我目前看不出您代码中出现的明显错误。然而，您在 removeTree 方法中返回了 null，这可能会导致一些问题。如果您在其中执行了删除操作，您应该返回删除后的树，而不是 null。另外，请确保在 removeTree 方法中正确处理您想要实现的子树删除逻辑，以避免出现空指针异常。
英文:
I'm studying trees in Java using an ArrayList, and I'm trying to implement a method to remove an entire subtree from a child node on my tree, but I keep getting a NullPointerException error.
Here's my code:
public class GeneralTree<Tree>
{
private Tree data = null; //create a tree
private List<GeneralTree> children = new ArrayList<>(); //create an arraylist
private GeneralTree parent = null; //create a parent
public GeneralTree(Tree data) //constructor
{
this.data = data;
}
public void addChild(GeneralTree child) //create a child method to create a child
{
child.setParent(this);
this.children.add(child);
}
public void addChild(Tree data) //create a method to put data into the children
{
GeneralTree<Tree> newChild = new GeneralTree<>(data);
this.addChild(newChild);
}
public void addChildren(List<GeneralTree> children) //create a method to add children to a parent
{
for(GeneralTree treeAdd: children)
{
treeAdd.setParent(this);
}
this.children.addAll(children);
}
public List<GeneralTree> getChildren() //get the children
{
return this.children;
}
public Tree getData() //get the data in the children
{
return data;
}
public void setData(Tree data) //set the data of the children together
{
this.data = data;
}
public void setParent(GeneralTree parent) //set the parent together
{
this.parent = parent;
}
public GeneralTree getParent() //get the parent
{
return this.parent;
}
public boolean isEmpty()
{
return this.children.isEmpty();
}
public List removeSubtree(GeneralTree childs)
{
GeneralTree removes = removeTree(this.parent);
return removes.children;
}
removeSubTree() and removeTree() methods to implement this
public List removeSubtree(GeneralTree childs)
{
GeneralTree removes = removeTree(this.parent);
return removes.children;
}
public GeneralTree removeTree(GeneralTree remover)
{
return null;
}
main method
public static void main(String[] args)
{
GeneralTree<String> root = new GeneralTree<>("Root"); //create a root node
GeneralTree<String> child1 = new GeneralTree<>("Child 1"); //first child node
child1.addChild("Grandchild 1"); //first grandchild node
child1.addChild("Grandchild 2"); //second grandchild node
GeneralTree<String> child2 = new GeneralTree<>("Child 2"); //second child node
child2.addChild("Grandchild 3"); //third grandchild node
root.addChild(child1);
root.addChild(child2);
root.addChild("Child 3"); //third child node
root.addChildren(Arrays.asList(new GeneralTree<>("Child 4"), new GeneralTree<>("Child 5"), new GeneralTree<>("Child 6")));//add fourth, fifth, and sixth children nodes
System.out.println(root.isEmpty()? "Empty": "Not Empty");
root.removeSubtree(child1);
for(GeneralTree node: root.getChildren()) //get and print the children as long as they're under the root
{
System.out.println(node.getData()); //get the data
}
}
}
I'm not fully sure where I've gone wrong, but I think the problem is that I'm using a remove Object method to try & remove a series of elements from my array list. Is that right, or am I going about this process the wrong way?
答案1
得分: 0
removeTree 方法始终返回 null。
removeSubtree 方法返回 removes.children，但 removes 对象始终为 null。
你应该实现 removeTree 方法。
英文:
The removeTree method returns always null.
The removeSubtree method returns removes.children but the removes object is always null.
You should implement the removeTree method
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