Java null pointer exception on recursive binary tree method

Question

this method is giving me a null pointer exception and I don't know why that is. Is there something wrong with the recursion code?

 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();

}

childrenRight or childrenLeft is null. use your debugger to identifiy why. — nano_nano, Oct 22 '15 at 13:09

score 3 · Accepted Answer · answered Oct 22 '15 at 13:10

Your isLeaf() check is not sufficient, since a node in a binary tree may have a single child, so you must add null checks :

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();

}

score 2 · Answer 2 · answered Oct 22 '15 at 13:09

2

do a null check on childrenRight and childrenLeft before making the function call

answered Oct 22 '15 at 13:09

AbtPst

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Java null pointer exception on recursive binary tree method

2 Answers2