在recusive二叉樹方法上的Java空指針異常

Question

這種方法給了我一個空指針異常，我不知道爲什麼，這是遞歸代碼有問題。我無法弄清楚。

public void clearAllSelections(){ 
    //Recursively clear all the selections in the sub-tree of this node 
    //basis: 
    isSelected = false; 
    if(isLeaf()) return; 

    //recursion: 
    childrenRight.clearAllSelections(); 
    childrenLeft.clearAllSelections(); 

} 

Answer 1

你isLeaf()檢查是不夠的面前，因爲在二叉樹中的節點可以有一個孩子，所以你必須添加null檢查：

public void clearAllSelections(){ 
    //Recursively clear all the selections in the sub-tree of this node 
    //basis: 
    isSelected = false; 
    if(isLeaf()) return; 

    //recursion: 
    if (childrenRight != null) 
     childrenRight.clearAllSelections(); 
    if (childrenLeft != null) 
     childrenLeft.clearAllSelections(); 

} 

Answer 2

做childrenRight和childrenLeft空校驗使函數調用