CODEWITHSUNDEEP
javacastingcomparable
Jon Plotner
Jon Plotner

Reputation: 61

java.lang.String cannot be cast to TreeComparable

TreeComparable is a Comparable interface.

The Error:

java.lang.String cannot be cast to TreeComparable

This is the line giving me the error 

if (((TreeComparable) r.getInfo()).compareTo((TreeComparable) p.getInfo()) < 0 )

And here is the method for that line:

public void insertBST(Object o) {
    ObjectTreeNode p, q;

    ObjectTreeNode r = new ObjectTreeNode(o);
    if (root == null)
        root = r;
    else {
        p = root;
        q = root;
        while (q != null) {
            p = q;
            if (((TreeComparable)(r.getInfo())).compareTo((TreeComparable)(p.getInfo())) < 0 )
                q = p.getLeft();
            else
                q = p.getRight();
        }
        if (((TreeComparable)(r.getInfo())).compareTo((TreeComparable)(p.getInfo())) < 0)
            setLeftChild(p, r);
        else
            setRightChild(p, r);
    }
}

Note: BST stands for binary search tree.

The getInfo method of the ObjectTreeNode class:

private Object info;
public Object getInfo() {
    return info;
}

and finally, I don't know if these will help, but my TreeComparable compareTo declaration:

int compareTo(Object o);

and the compareTo method in the (Word) class:

String word;        
public int compareTo(Object o) {
    Word w = (Word) o;
    return this.word.compareTo(w.getWord());
}

The Help is greatly appreciated.

Upvotes: 0

Views: 207

Answers (1)

Muhammad Kashif Nazar
Muhammad Kashif Nazar

Reputation: 23965

This is because String does not implement the interface TreeComparable. There is a an interface Comparable that String implements. String can be upcasted to this interface.

Upvotes: 1

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