Einführung in die objektorientierte Programmierung

Überprüfung, ob ein binärer Baum ein SearchTree ist (sortiert) mit drei Methoden

import java.util.*;

class BinaryTreeNode{
   private int entry;
   private BinaryTreeNode leftChild;
   private BinaryTreeNode rightChild;
   
   static int alt=0;
   static int neu=0;
   
   static ArrayList<Integer> liste = new ArrayList<Integer>(); 
   
   public int getEntry(){
   return entry;
   }
   
   public BinaryTreeNode getLeft(){
   return leftChild;
   }
   
   public BinaryTreeNode getRight(){
   return rightChild;
   }
   
   public void setEntry(int e){
   entry=e;
   }
   
   public void setLeft(BinaryTreeNode e){
   leftChild=e;
   }
   
   public void setRight(BinaryTreeNode e){
   rightChild=e;
   }
   
   static public void inorder(BinaryTreeNode node){
   
   if (node != null) {
   inorder(node.getLeft());
   //System.out.println(node.getEntry());
   liste.add(node.getEntry());
   inorder(node.getRight());
   } // end of if 
   }
   
   static public boolean isSearchTree(BinaryTreeNode node){
   int alt =0; 
   int neu =0;
   inorder(node);
   for (Integer wert : liste ) {
   neu= wert;
   if (alt>neu) {
   return false;
   } // end of if
   System.out.println(wert);
   alt=neu;
   } // end of for
   return true;
   }
   
   static public boolean isSearchTree2(BinaryTreeNode node){
   if (node == null) {
   return true;
   }
   
   if (isSearchTree2(node.getLeft())==false) return false;
   neu=node.getEntry();
   System.out.println(node.getEntry());
   if (alt>neu) return false;
   alt=neu;
   if (isSearchTree2(node.getRight())==false) return false;
   return true;
   }
   
   static public boolean isSearchTree3(BinaryTreeNode old,
   BinaryTreeNode node){
   if (node == null) {
   return true;
   }
   
   if (isSearchTree3(old,node.getLeft())==false) return false;
   System.out.println(node.getEntry());
   if (old.entry>node.entry) return false;
   old.entry=node.entry;
   if (isSearchTree3(old,node.getRight())==false) return false;
   return true;
   }
   
   static public int getMaximum(BinaryTreeNode node){
   if (node==null) {
   return 0;
   } // end of if
   while (node.getRight()!= null) { 
   node=node.getRight();
   } // end of while
   return node.getEntry();
   }
   
   public static void main(String[] args){
   
   BinaryTreeNode root= new BinaryTreeNode();
   root.setEntry(5);
   
   BinaryTreeNode neu= new BinaryTreeNode();
   neu.setEntry(3);
   root.setLeft(neu);
   
   neu.setRight(new BinaryTreeNode());
   neu.getRight().setEntry(4);
   
   neu= neu.getRight();
   neu.setLeft(new BinaryTreeNode());
   neu.getLeft().setEntry(4);
   
   neu.setRight(new BinaryTreeNode());
   neu.getRight().setEntry(5);
   
   root.setRight(new BinaryTreeNode());
   root.getRight().setEntry(7);
   
   //root=null;
   
   System.out.println(BinaryTreeNode.isSearchTree(root)); 
   System.out.println();
   
   System.out.println(BinaryTreeNode.isSearchTree2(root));
   System.out.println();
   
   BinaryTreeNode old = new BinaryTreeNode();
   old.setEntry(0);
   System.out.println(BinaryTreeNode.isSearchTree3(old,root));
   System.out.println();
   
   //System.out.println(BinaryTreeNode.getMaximum(root));
   
   }
   
   }