Java递归二叉树方法的空指针异常

Question

这个问题已经有答案了:

What is a NullPointerException, and how do I fix it? (12 个回答)

已关闭 7 年前。

这个方法给了我一个空指针异常，我不知道为什么会这样。递归代码有问题吗？

 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

您的 isLeaf() 检查不够，因为二叉树中的节点可能只有一个子节点，因此您必须添加空检查:

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();

}