StackOverflowException引起的遞歸

Question

我目前正在編寫一個程序來幫助寫Lore。每個書對象都可以是父母並且有孩子。這意味着每個孩子都可以有孩子等無限。我正在處理一個ToString（）方法，它可以使用遞歸來解釋這個問題，但我一直在收到一個StackOverflowException。

我知道這意味着什麼，但我對我如何解決它有疑問。我對C＃相當陌生，但擁有相當多的Java經驗，所以如果你知道一個技巧或者我錯過了什麼，請讓我知道！

所以我的問題是：如何避免StackOverflow異常？問題是在GetAllChildren（）

編輯：

運行測試後，我應該得到的東西是這樣的：

Name: a 
Children: 
b 
c 
    d 
e 

與@lc代碼。我得到以下輸出：

Name: a 
Children: No Children b 
c 
e 
    b 
c 
e 
    b 
c 
e 

這裏是類：

class Book 
{ 
    private String name; 
    private Book[] children; 
    private StringBuilder text; 
    private Boolean isParent; 

    public Book(String name, Book[] children, StringBuilder text, Boolean isParent) 
    { 
     this.name = name; 
     this.children = children; 
     this.text = text; 
     this.isParent = isParent; 
    } 

    /** 
    * Most likely all possible Constructors 
    * */ 
    public Book(String name, Book[] children) : this(name, children, new StringBuilder("No Text"), true) { } 
    public Book(String name, String text) : this(name, new Book[0], new StringBuilder(text), false) { } 
    public Book(String name, StringBuilder text) : this(name, new Book[0], text, false) { } 
    public Book(String name) : this(name, new Book[0], new StringBuilder("No Text"), false) { } 
    public Book(Book[] children, String text) : this("Unnamed Book", children, new StringBuilder(text), true) { } 
    public Book(Book[] children, StringBuilder text) : this("Unnamed Book", children, text, true) { } 
    public Book(Book[] children) : this("Unnamed Book", children, new StringBuilder("No Text"), true) { } 
    public Book(StringBuilder text) : this("Unnamed Book", new Book[0], text, false) { } 
    public Book() : this("Unnamed Book", new Book[0], new StringBuilder("No Text"), false) { } 

    public String Name 
    { 
     get { return name; } 
     set { name = value; } 
    } 

    public Book[] Children 
    { 
     get { return children; } 
     set { children = value; } 
    } 

    /** 
    * Will Return the StringBuilder Object of this Text 
    * */ 

    public StringBuilder Text 
    { 
     get { return text; } 
     set { text = value; } 
    } 

    public Boolean IsParent 
    { 
     get { return isParent; } 
     set { isParent = value; } 
    } 

    private void GetAllChildren(Book book, StringBuilder sb) 
    { 
     if (book.isParent) 
     { 
      GetAllChildren(book, sb); 
     } 
     else 
     { 
      sb.Append("\t"); 
      foreach (Book b in children) 
      { 
       sb.Append(b.Name + "\n"); 
      } 
     } 
    } 

    public override String ToString() 
    { 
     StringBuilder sChildren = new StringBuilder("No Children"); 
     if (children.Length != 0) 
     { 
      GetAllChildren(this, sChildren); 
     } 

     return "Name: " + name + "\n" + 
      "Children: " + sChildren.ToString(); 
    } 
} 

Answer 1

我想你的意思是：

if (book.isParent) 
{ 
    foreach (var child in book.Children) 
     GetAllChildren(child, sb); 
} 

否則你只是調用GetAllChildren方法具有相同的參數（book, sb）一遍又一遍。

---

附註 - 你仍然有一些問題，因爲在GetAllChildren停止條件是通過迭代的孩子，當它不應該（如果不是家長，它不應該有孩子）。它應該返回它自己的名字。此外，每個孩子還應該在上面的foreach循環中追加它的名字（或者實際上，每本書都應該附加自己的名字）。 （注意這些變化）的方法應該是靜態的，因爲它與任何給定的實例都不相關（這引出了下面的建議）。

---

建議 - 我建議像下面代替（未經測試，需要在格式化一些工作）：

//name changed to reflect what it really does 
//also changed to be an instance method (we no longer pass in a Book) 
//added listThisBooksName parameter to allow supressing the topmost book's output 
private void AppendAllChildren(StringBuilder sb, int level = 0, 
    bool listThisBooksName = false) 
{ 
    if (listThisBooksName) 
    { 
     //append ourself here 

     //first indent however far we need to 
     sb.Append(new String('\t', level)); 

     //now add our name 
     sb.Append(this.Name); 

     //and a newline (you can strip the last one later if you want) 
     sb.Append('\n'); 
    } 

    //forget the "isParent" property, just check if it has any children 
    //we don't need Children.Any() because the foreach will just iterate 0 times 
    //you might also consider using a List<Book> instead of an array for Children 
    if (this.Children != null) 
     foreach (var child in this.Children) 
      child.AppendAllChildren(sb, level+1, true); 
} 

Answer 2

這不是問題：

if (book.isParent) 
    { 
     GetAllChildren(book, sb); 
    } 

你再次調用相同的方法？我認爲上面應該遍歷孩子，併爲每個孩子Book致電GetAllChildren。只有輸出名稱如果您的Book不有任何孩子。

Answer 3

您的遞歸在同一本書上遞歸，而該書的IsParent爲true。如果這本書是父母，你可能想要通過所有的孩子遞歸。