java - Delete a node in Binary Search Tree -

i have test code bst. bst created, node deletion not working properly. suggest if below delete code correct or modification in delete method helpful.

public class binarysearchtree {   public binarysearchtree() {     super();   }    private class binarysearchtreenode{     private int data;     private binarysearchtreenode left;     private binarysearchtreenode right;      public binarysearchtreenode(){     }      public binarysearchtreenode(int data){       this.data = data;     }      public void setdata(int data) {       this.data = data;     }      public int getdata() {       return data;     }      public void setleft(binarysearchtree.binarysearchtreenode left) {       this.left = left;     }      public binarysearchtree.binarysearchtreenode getleft() {       return left;     }      public void setright(binarysearchtree.binarysearchtreenode right) {       this.right = right;     }      public binarysearchtree.binarysearchtreenode getright() {       return right;     }   }    public binarysearchtreenode insertrec(binarysearchtreenode root,int data){     if(root == null){       root = new binarysearchtreenode();        root.setdata(data);       root.setleft(null);       root.setright(null);     }else{         if(data < root.getdata())           root.setleft(insertrec(root.getleft(), data));         else if(data > root.getdata())           root.setright(insertrec(root.getright(), data));     }      return root;   }    public void insertnonrec(binarysearchtreenode root,int data){     if(root == null){       root = new binarysearchtreenode(data);        root.setleft(null);       root.setright(null);     }else{       if(data < root.getdata()){         if(root.getleft() != null){           insertnonrec(root.getleft(),data);         }else{           root.setleft(new binarysearchtreenode(data));         }       }else if(data > root.getdata()){         if(root.getright() != null){           insertnonrec(root.getright(), data);         }else{           root.setright(new binarysearchtreenode(data));         }       }     }   }    public void delete(binarysearchtreenode root,int data){     binarysearchtreenode temp;     if(root == null){       system.out.println("no elemets in bst.");     }else if(data < root.getdata()){       delete(root.getleft(),data);     }else if(data > root.getdata()){       delete(root.getright(),data);     }else{       if((root.getleft() != null) && (root.getright() != null)){         // replace largest in left subtree          temp = findmax(root.getleft());         root.setdata(temp.getdata());         delete(root.getleft(),temp.getdata());       }else if(root.getleft() != null || root.getright() != null){         // 1 child         if(root.getleft() == null){           //root = root.getright();           root.setdata(root.getright().getdata());           root.setright(null);         }else if(root.getright() == null){           //root = root.getleft();           root.setdata(root.getleft().getdata());           root.setleft(null);         }       }else{         root = null;       }     }   }    public binarysearchtreenode findmax(binarysearchtreenode root){     if(root == null)       return null;      while(root.getright() != null)       root = root.getleft();      return root;   }    public binarysearchtreenode findmin(binarysearchtreenode root){     if(root == null)       return null;      while(root.getleft() != null)       root = root.getleft();      return root;   }    public void inorderrec(binarysearchtreenode root){     if(root != null){       inorderrec(root.getleft());       system.out.print(root.getdata() + " ");       inorderrec(root.getright());     }   }    public static void main(string args[]){     binarysearchtree tree = new binarysearchtree();     binarysearchtreenode root = tree.insertrec(null, 10);      tree.insertnonrec(root, 5);     tree.insertnonrec(root, 20);     tree.insertnonrec(root, 4);     tree.insertnonrec(root, 8);     tree.insertnonrec(root, 12);     tree.insertnonrec(root, 30);     tree.insertnonrec(root, 11);     tree.insertnonrec(root, 13);      system.out.println("inorder traversal :");     tree.inorderrec(root);      tree.delete(root, 20);      system.out.println("");     system.out.println("inorder traversal :");     tree.inorderrec(root);   } } 

output :

inorder traversal : 4 5 8 10 11 12 13 20 30   inorder traversal : 4 5 8 10 11 12 13 11 30 

root = null; doesn't think does. changes value of local variable only. not change tree. brief metaphor:

think of classroom of students. students nodes in tree. point @ each other, defines parenthood in tree. if student (say john, i.e. parameter of function) come along , point @ 1 of students in 'tree' (say sarah), saying root = null; equivalent john pointing nowhere, not change sarah nor other students pointing at.

sure there holes in metaphor, hope basic idea.

you instead need node.setleft(null); or node.setright(null); change tree.

this require quite few changes, i'll leave figure out (this or this may of help), note you'll have check left , right children instead of (just) root.

i suggest take @ red-black trees (or similar) provide more efficient means of deleting nodes , keeps tree balanced.