我需要把下面這個有缺失的代碼實現，在這里，這個代碼的構造函數是不完整的，如何合理的完成構造函數的填充在完成構造函數部分之后，我需要在主函數中創建幾個節點， 然后使用findChild方法來找到每個節點的名字。怎么把findChild函數填充完整，這樣程序可以順利進行下面是代碼 package directory_explorer;import java.util.Map;import java.util.Collection;import java.util.HashMap;/** * The root of a tree representing a directory structure. */public class FileNode {    /** The name of the file or directory this node represents. */    private String name;    /** Whether this node represents a file or a directory. */    private FileType type;    /** This node's parent. */    private FileNode parent;    /**     * This node's children, mapped from the file names to the nodes. If type is     * FileType.FILE, this is null.     */    private Map<String, FileNode> children;    /**     * A node in this tree.     *     * @param name     *            the file     * @param parent     *            the parent node.     * @param type     *            file or directory     * @see buildFileTree     */    public FileNode(String name, FileNode parent, FileType type) {        this.name = name;        // TODO: complete this method.    }    /**     * Find and return a child node named name in this directory tree, or null     * if there is no such child node.     *     * @param name     *            the file name to search for     * @return the node named name     */    public FileNode findChild(String name) {        FileNode result = null;        // TODO: complete this method.        return result;    }    /**     * Return the name of the file or directory represented by this node.     *     * @return name of this Node     */    public String getName() {        return this.name;    }    /**     * Set the name of the current node     *     * @param name     *            of the file/directory     */    public void setName(String name) {        this.name = name;    }