I'd like to sort my objects of Type AVLNode by their key (type String). I instantiated a Comparator and want to apply the compareTo
Method on the String attribute. But, my IDE shows me the error Cannot resolve method compareTo
. I don't understand why I cant use the compareTo
method on a string an this point.
import java.util.*;
public class AVLTreeTest {
public static void main(String[] args){
Comparator<AVLNode>myComp2 = new Comparator<AVLNode>() {
@Override public int compare(AVLNode n1, AVLNode n2) {
return n1.getKey().compareTo(n2.getKey());
}
};
AVLNode<String, AVLNode> a1 = new AVLNode( "test3", new Cuboid (2,3,4,5,6,7) );
AVLNode<String, AVLNode> a2 = new AVLNode( "test2", new Cuboid (2,3,4,5,6,7) );
AVLNode<String, AVLNode> a3 = new AVLNode( "test8", new Cuboid (2,3,4,5,6,7) );
AVLNode<String, AVLNode> a4 = new AVLNode( "test1", new Cuboid (2,3,4,5,6,7) );
List<AVLNode> listOfNodes = new ArrayList<AVLNode>();
listOfNodes.add(a1);
listOfNodes.add(a2);
listOfNodes.add(a3);
listOfNodes.add(a4);
Collections.sort(listOfNodes, myComp2);
for (AVLNode node : listOfNodes){
System.out.println(node);
}
}
}
This is my AVLNode Class
public class AVLNode<K, V> {
private AVLNode<K, V> left, right, parent;
private int height = 1;
private K key;
private V value;
public AVLNode() {}
public AVLNode(K key, V value) {
this.key = key;
this.value = value;
}
public V getValue() {
return value;
}
public K getKey() {
return key;
}
}
What am I doing wrong?
AVLNode
is generic, parameterized with K
and V
. In your Comparator<AVLNode>
, AVLNode
is raw. That is, K
and V
are unknown. This means the compiler actually does not know if K
is Comparable
.
Try making it Comparator<AVLNode<String, ?>>
.
Unrelated, but also use new AVLNode<>(...)
.
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