Question

我还在学习，试图从保加利亚的java书中运行代码，但它无效。有人可以看看吗？

public class BinaryTree {
    public static class BinaryTreeNode<T> {
        private T value;
        private boolean hasParent;
        private BinaryTreeNode<T> leftChild;
        private BinaryTreeNode<T> rightChild;

        /**
         * Constructs a binary tree node.
         *
         * @param value      - the value of the node.
         * @param leftChild  - the left child of the node.
         * @param rightChild - the right child of the node.
         */
        public BinaryTreeNode(T value,
                              BinaryTreeNode<T> leftChild,
                              BinaryTreeNode<T> rightChild) {
            if (value == null) {
                throw new IllegalArgumentException(
                        "Cannot insert null value!");
            }

            this.value = value;
            this.leftChild = leftChild;
            this.rightChild = rightChild;
        }

        /**
         * Constructs a binary tree node with no children.
         *
         * @param value - the value of the node.
         */
        public BinaryTreeNode(T value) {
            this(value, null, null);
        }

        public T getValue() {
            return this.value;
        }

        public void setValue(T value) {
            this.value = value;
        }

        public BinaryTreeNode<T> getLeftChild() {
            return this.leftChild;
        }

        public void setLeftChild(BinaryTreeNode<T> value) {
            if (value == null || value.hasParent) {
                throw new IllegalArgumentException();
            }

            value.hasParent = true;
            this.leftChild = value;
        }

        public BinaryTreeNode<T> getRightChild() {
            return this.rightChild;
        }

        public void setRightChild(BinaryTreeNode<T> value) {
            if (value == null || value.hasParent) {
                throw new IllegalArgumentException();
            }

            value.hasParent = true;
            this.rightChild = value;
        }
    }

    // The root of the tree
    private BinaryTreeNode<T> root;

    /**
     * Constructs the tree.
     * @param value - the value of the node.
     * @param children - the children of the node.
     */
    public BinaryTree(T value, BinaryTree<T> leftChild,
                      BinaryTree<T> rightChild) {

        if (value == null) {
            throw new IllegalArgumentException();
        }

        BinaryTreeNode<T> leftChildNode =
                leftChild != null ? leftChild.root : null;
        BinaryTreeNode<T> rightChildNode =
                rightChild != null ? rightChild.root : null;
        this.root = new BinaryTreeNode<T>(
                value, leftChildNode, rightChildNode);
    }

    /**
     * Constructs the tree.
     * @param value - the value of the node.
     */
    public BinaryTreeNode<T> getRoot() {
        return this.root;
    }

    /**
     * @return the left child of the root.
     */
    public BinaryTreeNode<T> getLeftChildNode() {
        if (this.root != null) {
            return this.root.getLeftChild();
        }

        return null;
    }

    /**
     * Traverses binary tree in pre-order manner.
     * @param root - the binary tree to be traversed.
     */
    private void printPreOrder(BinaryTreeNode<T> root) {
        if (root == null) {
            return;
        }

        printPreOrder(root.getLeftChild());

        System.out.print(root.getValue() + " ");

        printPreOrder(root.getRightChild());
    }

    /**
     * Traverses and prints the binary
     * tree in pre-order manner.
     */
    public void printPreOrder() {
        printPreOrder(this.root);
        System.out.println();
    }
}

这里我在“树的根”下面的行“无法解析符号”T“”。

第二部分 - 测试：

public class BinaryTreeExample {
    public static void main(String[] args) {
// Create the binary tree from the sample.
        BinaryTree<Integer> binaryTree =
                new BinaryTree<Integer>(14,
                        new BinaryTree<Integer>(19,
                                new BinaryTree<Integer>(23),
                                new BinaryTree<Integer>(6,
                                        new BinaryTree<Integer>(10),
                                        new BinaryTree<Integer>(21))),
                        new BinaryTree<Integer>(15,
                                new BinaryTree<Integer>(3),
                                null));
// Traverse and print the tree in pre-order manner.
        binaryTree.printPreOrder();
    }
}

我得到“BinaryTree没有类型参数”。这是在编译之前从IntelliJ编辑器。当我尝试运行程序时，我也会遇到很多错误。如何解决这个问题？

Answer 1

此处BinaryTree<Integer> binaryTree您使用通用，但在声明BinaryTree（public class BinaryTree {）时，您没有使用通用。因此，您必须在BinaryTree声明中添加泛型或从创建BinaryTree对象中删除泛型。

Answer 2

要纠正错误，您应该将BinaryTree Integer的所有用法替换为BinaryTree，但将BinaryTree声明为泛型BinaryTree会更有意义。您的代码将树的节点声明为通用，但除非您希望在同一个树中使用不同类型的节点，否则应将树声明为通用树并使其节点遵循此类型。

Answer 3

这是工作代码：

public class BinaryTree<T> {
    public static class BinaryTreeNode<T>
    {
        // Contains the value of the node
        private T value;
        // Shows whether the current node has parent
        private boolean hasParent;
        // Contains the left child of the node
        private BinaryTreeNode<T> leftChild;
        // Contains the right child of the node
        private BinaryTreeNode<T> rightChild;

        /**
         * Constructs a binary tree node.
         * @param value - the value of the node.
         * @param leftChild - the left child of the node.
         * @param rightChild - the right child of the node.
         */
        public BinaryTreeNode(T value,
                              BinaryTreeNode<T> leftChild,
                              BinaryTreeNode<T> rightChild)
        {
            if (value == null) {
                throw new IllegalArgumentException(
                        "Cannot insert null value!");
            }
            this.value = value;
            this.leftChild = leftChild;
            this.rightChild = rightChild;
        }
        public BinaryTreeNode(T value)
        {
            this(value, null, null);
        }

        /**
         * @return the value of the node.
         */
        public T getValue() {
            return this.value;
        }

        /**
         * Sets the value of the node.
         * @param value - the value to be set.
         */
        public void setValue(T value) {
            this.value = value;
        }

        /**
         * @return the left child or null if it does not exists.
         */
        public BinaryTreeNode<T> getLeftChild() {
            return this.leftChild;
        }

        /**
         * Sets the left child.
         * @param value - the new left child to be set.
         */
        public void setLeftChild(BinaryTreeNode<T> value) {
            if (value == null || value.hasParent) {
                throw new IllegalArgumentException();
            }
            value.hasParent = true;
            this.leftChild = value;
        }

        /**
         * @return the right child or null if it does not exists.
         */
        public BinaryTreeNode<T> getRightChild() {
            return this.rightChild;
        }

        /**
         * Sets the right child.
         * @param value - the new right child to be set.
         */
        public void setRightChild(BinaryTreeNode<T> value) {
            if (value == null || value.hasParent) {throw new IllegalArgumentException();
            }
            value.hasParent = true;
            this.rightChild = value;
        }
    }

    // The root of the tree
    private BinaryTreeNode<T> root;

    /**
     * Constructs the tree.
     * @param value - the value of the node.
     * @param children - the children of the node.
     */
    public BinaryTree(T value, BinaryTree<T> leftChild,
                      BinaryTree<T> rightChild) {
        if (value == null) {
            throw new IllegalArgumentException();
        }
        BinaryTreeNode<T> leftChildNode =
                leftChild != null ? leftChild.root : null;
        BinaryTreeNode<T> rightChildNode =
                rightChild != null ? rightChild.root : null;
        this.root = new BinaryTreeNode<T>(
                value, leftChildNode, rightChildNode);
    }

    /**
     * Constructs the tree.
     * @param value - the value of the node.
     */
    public BinaryTree(T value) {
        this(value, null, null);
    }
    /**
     * @return the root of the tree.
     */
    public BinaryTreeNode<T> getRoot()
    {
        return this.root;
    }

/**
 * @return the left child of the root.
 * */
public BinaryTreeNode<T> getLeftChildNode()
{
    if (this.root != null)
    {
        return this.root.getLeftChild();
    }
    return null;
}
    /**
     * @return the right child of the root.
     */
    public BinaryTreeNode<T> getRightChildNode()
    {
        if (this.root != null)
        {
            return this.root.getRightChild();
        }
        return null;
    }
    /**
     * Traverses binary tree in pre-order manner.
     * @param root - the binary tree to be traversed.
     */
    private void printPreOrder(BinaryTreeNode<T> root) {
        if (root == null) {
            return;
        }

// 1. Visit the left child.
        printPreOrder(root.getLeftChild());
// 2. Visit the root of this subtree.
        System.out.print(root.getValue() + " ");
// 3. Visit the right child.
        printPreOrder(root.getRightChild());
    }

    /**
     * Traverses and prints the binary
     * tree in pre-order manner.
     */
    public void printPreOrder() {
        printPreOrder(this.root);
        System.out.println();
    }
}

没有从java书中运行示例程序

3 个答案: