我正在创建一个程序，它从一个文件中获取输入（在我的例子中，是学生姓名和他们的相关编号），并以带迭代器的预排序形式、带递归的post+inoorder形式打印出来。在我的驱动程序中，我已经成功地创建和添加了学生的名字+关联的数字+用预排序迭代器打印出来。然而，我的问题是，当我试图打印这两个递归方法时，我得到了一个“void type not allowed here”错误。这两个方法存储在一个binarytree类中，但是需要由驱动程序从binarysearchtree调用，我使用了super.“insert method name”（在下面找到了它的接口）。
驱动程序（最后两个打印语句出错）：

package driver;

import java.io.*;
import java.util.*;

public class Driver {

    private static Scanner file;
    static PrintWriter outputFilePrinter;
    static Scanner inputFileScanner;

    public static void main(String[] args) throws FileNotFoundException {

        Scanner inFile; //Declaring scanner obj
        PrintWriter printWriter = new PrintWriter("output.txt"); //Text file where results are printed to
        inFile = new Scanner(new File("input.txt")); //Text file where student names and associated number are read from

        BinarySearchTreeInterface<String> aTree = new BinarySearchTree<>() {}; //Giving access to BinarySearchTree methods

        while (inFile.hasNext()) { //Scans input file
            String name = inFile.nextLine(); //Assigns contents to string obj
            aTree.add(name); //Add string to a tree
        } //End while

        Iterator<String> traverse = aTree.getPreorderIterator(); //Using iterator to print tree in an "preorder" fashion    
            while (traverse.hasNext())
        printWriter.println(traverse.next()); //Prints tree

        printWriter.println("Postorder Recursive: " + aTree.postorderTraverse());
        printWriter.println("Inorder Recursive: " + aTree.inorderTraverse());

        printWriter.close(); //Closes file

    } //End Main

} //End Driver

binarytree类递归方法：

public void inorderTraverse() {
    inorderTraverse(root);
    }

    public void inorderTraverse(BinaryNode<T> node) {
        if (node != null) {
            inorderTraverse(node.getLeftChild());
            System.out.println(node.getData());
            inorderTraverse(node.getRightChild());
        }
    }

    public void postorderTraverse() {
        postorderTraverse(root);
    }

    public void postorderTraverse(BinaryNode<T> node) {
        if (node != null)
            return;
        postorderTraverse(root.getLeftChild());
        postorderTraverse(root.getRightChild());
        System.out.println(root.getData());
    }

binarysearchtree类，其中我使驱动程序可以访问两个递归方法：

public void inorderTraverse() {  
    super.inorderTraverse();
}

public void postorderTraverse() {
    super.postorderTraverse();
}

binarysearchtreeinterafce:如何在接口中列出它们

public void postorderTraverse();

public void inorderTraverse();