How can I solve Exception in thread “main” java.lang.NullPointerException error [duplicate]

Question

My code is: https://code.sololearn.com/#java

The error message happens in line: for(TreeNode<String> node: this.children )
This method is to get the leafNode of a tree. Can someone help me to fix my error? thanks!

Answer 1

so how can i fix this?

Answer 2

The link is to all the Java codes in SoloLearn.
NullPointerException means that you have a null variable which is used as if its not null, which means that this.children is null.

Answer 3

add an if statement to check if children is null

Answer 4

it will be inside the for loop?

Answer 5

Yes

Answer 6

I did like below but it does not work

for(TreeNode<String> node: this.children ){
if(node.children.isEmpty()){
nodes.add(node);
} else {
nodes.addAll(getLeafNodes());
}

Answer 7

do == null

Answer 8

if(node.children() == null ) ??

Answer 9

i fixed it. Thanks!

Answer 10

Mark my answer as best if it helped to solve your problem :-)