Why is false being returned in this function

Question

In my program below, I set the variable th as true in the second if statement. I'm curious why it later returns as false.

public boolean nodeExist(TreeNode Tree, T value){

    boolean th = false;

    if(Tree.getValue()!= null){

        if(value == Tree.getValue()){

            th = true;

        }else{

            if(value.compareTo((T) Tree.getValue()) < 0){

                nodeExist(Tree.getLeft(), value);

            }else{

                nodeExist(Tree.getRight(), value);
            }

        }

    }else{

        th = false;

    }

    return th;

}

BTW: `if` is no function! It's an control flow statement. – gregor Apr 25 '10 at 20:35 — gregor, Apr 25 '10 at 20:35
It's not as bad as `if loop`. `:P` – Xavier Ho Apr 26 '10 at 04:32 — Xavier Ho, Apr 26 '10 at 04:32

score 5 · Accepted Answer · answered Apr 25 '10 at 20:32

5

You probably look at a recursive call which sets th to true. But when that call returns to its caller, that th is still at false, and that's then returned. You need to assign the recursive callee's result:

        if(value.compareTo((T) Tree.getValue()) < 0){

            th = nodeExist(Tree.getLeft(), value);

        }else{

            th = nodeExist(Tree.getRight(), value);
        }

answered Apr 25 '10 at 20:32

Johannes Schaub - litb

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Or, change the assignment to a return statement. – Matt Ball Apr 25 '10 at 20:33

score 1 · Answer 2 · edited May 23 '17 at 12:04

You already got your answer. In future, to prevent mistakes like this, it's better to just return the value right away if you can. IT'S OKAY to have multiple return; if used properly, it can read to more readable code.

public boolean nodeExist(TreeNode Tree, T value){
    if (Tree.getValue() == null) return false;

    if (value == Tree.getValue()) return true;

    if (value.compareTo((T) Tree.getValue()) < 0) {
       return nodeExist(Tree.getLeft(), value);
    } else {
       return nodeExist(Tree.getRight(), value);
    }
}

Why is false being returned in this function

3 Answers3

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