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POWhen reading from a Scanner in a loop, it goes into an infinite loop
 

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  1. POWhen reading from a Scanner in a loop, it goes into an infinite loop
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    <p>Two problems here. When I try to traverse this home-grown binary tree using a "recursive iterator" (an iterator that traverses the tree recursively, puts the elements into a queue, and then removes the elements from the front of the queue). The iterator tends to iterate backwards (greatest to least) instead of inorder (least to greatest). Also, when I try to read user input from a <code>Scanner</code> using <code>nextInt()</code>, the program goes into an infinite loop. I'm trying to catch the <code>InputMismatchException</code> when the user inputs an invalid number.<br> In the below code segment, I'm catching the InputMismatchException when the user doesn't input a number so that the program continues normally.<br> Testing file:</p> <pre><code>package assignments.unit9; import java.util.*; import static java.lang.System.*; import java.io.*; public class BinaryTreeTest { private static BinaryTree&lt;Item&gt; tree; static Scanner user; public static void main(String... args) { user = new Scanner(System.in); int choice; do { out.println("1. Read data from disk"); out.println("2. Print the tree in order"); out.println("3. Search the tree"); out.println("4. Delete from the tree"); out.println("5. Count the nodes in the tree"); out.print("0. Quit\n&gt;"); try { choice = user.nextInt(); } catch(InputMismatchException e) { choice = -1; } switch(choice) { case 0: exit(0); case 1: try { readFromDisk(); } catch(FileNotFoundException e) { err.println("Sorry, but the file could not be opened: " + e.getMessage()); } break; case 2: if(tree == null) { err.println("Must read file first"); break; } printTree(); break; case 3: if(tree == null) { err.println("Must read file first"); break; } searchTree(); break; case 4: if(tree == null) { err.println("Must read file first"); break; } // deleteFromTree(); break; case 5: if(tree == null) { err.println("Must read file first"); break; } countNodes(); break; default: err.println("Invalid choice. The available choices are:"); break; } } while(choice != 0); } public static void readFromDisk() throws FileNotFoundException { Scanner file = new Scanner(new File("file20.txt")); tree = new BinaryTree&lt;Item&gt;(); if(file.hasNextInt()) file.nextInt(); //skip the first integer while(file.hasNextInt()) { tree.add(new Item(file.nextInt(), file.nextInt())); } } public static void printTree() { tree.inorder(); } public static void searchTree() { out.println("Enter ID value to search for (-1 to return)"); int search; Item searched; while((search = user.nextInt()) != -1) { out.println(searched = tree.find(new Item(search, 0))); if(searched == null) out.println("\b\b\b\b\bNo such part in stock"); } } public static void countNodes() { out.println(tree.countNodes()); } } </code></pre> <p>Here, in the BinaryTree class, I try to traverse it recursively (see iterator() and asQueue()): </p> <pre><code>package assignments.unit9; import java.util.*; public class BinaryTree&lt;E extends Comparable&lt;E&gt;&gt; implements Iterable&lt;E&gt; { private TreeNode&lt;E&gt; root; public void add(E value) { if(root == null) { root = new TreeNode&lt;E&gt;(value); } else { TreeNode&lt;E&gt; temp = root, upFrom = null; boolean goesOnLeft = false; while(true) { if(temp == null) { if(goesOnLeft) upFrom.setLeft(new TreeNode&lt;E&gt;(value)); else upFrom.setRight(new TreeNode&lt;E&gt;(value)); break; } else if(temp.getValue().compareTo(value) &lt; 0) //goes on left { upFrom = temp; temp = upFrom.getLeft(); goesOnLeft = true; continue; } else //goes on right { upFrom = temp; temp = upFrom.getRight(); goesOnLeft = false; continue; } } } } public void inorder() { try { inorder(root); } catch(StackOverflowError e) { System.err.println("Increase stack size to print remaining elements"); } } private void inorder(TreeNode&lt;E&gt; t) { if(t == null) return; inorder(t.getLeft()); System.out.println(t.getValue()); inorder(t.getRight()); } private ArrayDeque&lt;E&gt; asQueue(TreeNode&lt;E&gt; t, ArrayDeque&lt;E&gt; toAdd) { try { if(toAdd == null) toAdd = new ArrayDeque&amp;lt;E&gt;(); if(t == null) return toAdd; asQueue(t.getLeft(), toAdd); toAdd.addLast(t.getValue()); asQueue(t.getRight(), toAdd); ret: return toAdd; } catch(StackOverflowError e) { throw new InternalError(); } } public Iterator&lt;E&gt; iterator() { return new Iterator&lt;E&gt;() { private ArrayDeque&lt;E&gt; d = asQueue(root, null); public E next() { return d.pop(); } public boolean hasNext() { return !d.isEmpty(); } public void remove() { throw new UnsupportedOperationException(); } }; } public int countNodes() { int toReturn = 0; for(E elem : this) ++toReturn; return toReturn; } public E find(E toFind) { for(E elem : this) { if(elem.equals(toFind)) return elem; } return null; } } </code></pre> <p>TreeNode class: </p> <pre><code>package assignments.unit9; import java.util.Objects; public class TreeNode&lt;T&gt; { private T value; private TreeNode&lt;T&gt; left, right; /** * Constructs a new TreeNode value with the left and right pointers {@code null}. * * @param value the item to be referenced * * @throws NullPointerException if {@code value} is {@code null}. */ public TreeNode(T value) { this.value = Objects.requireNonNull(value); } /** * Constructs a new TreeNode value with the specified left and right pointers. * * @param value the item to be referenced * @param left the TreeNode value to the left. * @param right the TreeNode value to the right. * * @throws NullPointerException if {@code value} is {@code null}. */ public TreeNode(T value, TreeNode&lt;T&gt; left, TreeNode&lt;T&gt; right) { this.value = Objects.requireNonNull(value); this.left = left; this.right = right; } public T getValue() { return value; } public TreeNode&lt;T&gt; getLeft() { return left; } public TreeNode&lt;T&gt; getRight() { return right; } public void setValue(T value) { this.value = Objects.requireNonNull(value); } public void setLeft(TreeNode&lt;T&gt; left) { this.left = left; } public void setRight(TreeNode&lt;T&gt; right) { this.right = right; } } </code></pre> <p>Data type (Item): </p> <pre><code>package assignments.unit9; import java.util.*; public class Item implements Comparable&lt;Item&gt; { private int myID; private int myInv; //Comparators public static class IDComparator implements Comparator&lt;Item&gt; { public int compare(Item i1, Item i2) { return i1.getID() - i2.getID(); } @Override public boolean equals(Object obj) { return obj instanceof IDComparator; } } public static class InvComparator implements Comparator&lt;Item&gt; { public int compare(Item i1, Item i2) { return i1.getInv() - i2.getInv(); } @Override public boolean equals(Object obj) { return obj instanceof InvComparator; } } public Item(int id, int inv) { myID = id; myInv = inv; } public int getID() { return myID; } public int getInv() { return myInv; } public int compareTo(Item i) { if(i == null) throw new NullPointerException(); return this.myID - i.myID; } @Override public boolean equals(Object otherObject) { Item i; try { i = (Item) otherObject; return myID == i.myID; } catch(ClassCastException ex) { return false; } } public String toString() { return "ID: " + myID + "\tInventory number: " + myInv + "\n"; } @Override public int hashCode() { return Objects.hash(myID, myInv); } } </code></pre> <p>And here's the input file. Sorry if that's a lot:</p> <pre><code>20 196 60 18618 64 2370 65 18410 56 18465 27 19967 45 17911 96 184 14 18871 69 14088 92 18061 3 206 31 13066 8 12705 14 15917 51 15814 60 15320 82 8303 90 7282 73 12328 63 </code></pre>
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    1. This table or related slice is empty.
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    1. This table or related slice is empty.
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    1. COIsn't your program exiting when you enter `0` as the input?
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      1. POWhen reading from a Scanner in a loop, it goes into an infinite loop
      1. USVishal K
 

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