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При проверке метода contains возникает ошибка. Если мы вводили значение, которое есть в древе, программа возвращает true, как и задумано, если же значение не находится в древе, я получаю Exception in thread "main" java.lang.NullPointerException.

package Tree;

import Tree.Comparat.TreeInterface;

/**
 * Created by Spring on 15.12.2017.
 */
public class Tree<E extends Comparable> implements TreeInterface<E> {

    Node<E> root;

    public Tree(E value){
        root = new Node<E>(value);
    }

    public Node<E> getRoot() {
        return root;
    }

    @Override
    public void insert(E element) {
        Node<E> newNode = new Node<E>(element);
        if (root == null) {
            root = newNode;
        }
        else {
            recursiveInsert(root, newNode);
        }
    }

    public void recursiveInsert(Node<E> current, Node<E> newNode){
        if((current.compareTo(newNode) < 0) && current.getRight()==null){
            current.setRight(newNode);
        }
        else if((current.compareTo(newNode) < 0) && current.getRight()!=null) {
            recursiveInsert(current.getRight(), newNode);
        }

        else if((current.compareTo(newNode) > 0) && current.getLeft()==null){
            current.setLeft(newNode);
        }
        else if((current.compareTo(newNode) > 0) && current.getLeft()!=null) {
            recursiveInsert(current.getLeft(), newNode);
        }
    }

    @Override
    public void display() {

        Node<E> root = getRoot();
        recursiveDisplay(root);

    }

    public void recursiveDisplay(Node<E> current){

        Node<E> leftNode = current.getLeft();
        Node<E> rightNode = current.getRight();

        if(leftNode !=null){
            leftNode.nodeDisplay();
            recursiveDisplay(leftNode);
        }
        if(rightNode !=null){
            rightNode.nodeDisplay();
            recursiveDisplay(rightNode);
        }
    }

    @Override
    public boolean contains(E element) {

        Node<E> root = getRoot();
        Node<E> nodeToFind = new Node<E>(element);

            return recursiveFind(root, nodeToFind)!= null;

    }

    public Node<E> recursiveFind(Node<E> current, Node<E> nodeToCompare){

        if(current.compareTo(nodeToCompare) == 0)
            return current;

        else if (current.compareTo(nodeToCompare) > 0)
            return recursiveFind(current.getLeft(),nodeToCompare);

        else if (current.compareTo(nodeToCompare) < 0)
            return recursiveFind(current.getRight(),nodeToCompare);


        return  null;
    }


    @Override
    public boolean delete(int a) {
        return false;
    }


    public static void main(String[] args) {
        Tree<Integer> tree = new Tree<Integer>(10);
        tree.insert(4);
        tree.insert(88);
        tree.insert(5);
        tree.insert(6);
        tree.insert(20);
        tree.insert(22);
        System.out.println(tree.contains(10));
        System.out.println(tree.contains(5));
        System.out.println(tree.contains(6));
        System.out.println(tree.contains(22));
        System.out.println(tree.contains(666));
    }
}

Результат работы программы:

Exception in thread "main" java.lang.NullPointerException
    at Tree.Tree.recursiveFind(Tree.java:82)
    at Tree.Tree.recursiveFind(Tree.java:89)
    at Tree.Tree.recursiveFind(Tree.java:89)
    at Tree.Tree.contains(Tree.java:76)
    at Tree.Tree.main(Tree.java:115)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
true
true
true
true
    at java.lang.reflect.Method.invoke(Method.java:498)
    at com.intellij.rt.execution.application.AppMain.main(AppMain.java:144)

Process finished with exit code 1
zRrr
  • 5,257
user236997
  • 43

1 Answers1

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Достаточно было внести проверку на null в рекурсивном блоке.

user236997
  • 43