The basic concept of binary tree: binary tree is defined recursively, and its nodes are divided into left and right subtrees. Logically, binary tree consists of five forms: 1) empty binary tree 2) binary tree with only one root node 3) left subtree 4) right subtree 5) complete binary tree

Creation of Binary Tree

private static class Node{
	private char val;
	private Node left;
	private Node right;
	private Node(char val) {
		this.val=val;
	}
}
public static Node buildTree(){
	Node a=new Node('A');
	Node b=new Node('B');
	Node c=new Node('C');
	Node d=new Node('D');
	Node e=new Node('E');
	Node f=new Node('F');
	Node g=new Node('G');
	Node h=new Node('H');
	a.left=b; a.right=c;
	b.left=d;b.right=e;
	c.left=f;c.right=g;
	e.right=h;
	return a;	
}

Front, middle and post-order traversal of binary trees

Preorder traversal: If the binary tree is empty, return null; otherwise

1) Access to the root node

2) Preorder traversal of left subtrees

2) Preorder traversal of right subtrees

Intermediate traversal: If the binary tree is empty, it returns null; otherwise, it returns null.

1) Mid-order traversal of left subtrees

2) Access to the root node

3) Mid-order traversal of right subtrees

Post-order traversal: If the binary tree is empty, it returns null; otherwise, it returns null.

1) Post-order traversal of left subtrees

2) Follow-up traversal of right subtree

3) Access to the root node

public static void preOrderTraversal(Node root) {
		//Line traversal
		//Preorder traversal of root + left subtree + right subtree
		
    if(root==null) {
		return ;
	}
	System.out.println(root);
	preOrderTraversal(root.left);
	preOrderTraversal(root.right);
}
public static void inOrderTraversal(Node root) {
    //Sequential traversal
	//Mid-order traversal of left subtree + root + right subtree
	if(root==null) {
		return ;
	}
	inOrderTraversal(root.left);
	System.out.println(root);
	inOrderTraversal(root.right);
}
public static void postOrderTraversal(Node root) {
	//Follow-up traversal of binary trees
	if(root==null) {
		return;
	}
	postOrderTraversal(root.left);
	postOrderTraversal(root.right);
	System.out.println(root);
}

Complete code:

public class BineryTree {
	private static class Node{
		private char val;
		private Node left;
		private Node right;
		private Node(char val) {
			this.val=val;
		}
	}
	public static Node buildTree(){
		Node a=new Node('A');
		Node b=new Node('B');
		Node c=new Node('C');
		Node d=new Node('D');
		Node e=new Node('E');
		Node f=new Node('F');
		Node g=new Node('G');
		Node h=new Node('H');
		a.left=b; a.right=c;
		b.left=d;b.right=e;
		c.left=f;c.right=g;
		e.right=h;
		return a;
	}
	public static void preOrderTraversal(Node root) {
		//Line traversal
		//Preorder traversal of root + left subtree + right subtree
		if(root==null) {
			return ;
		}
		System.out.println(root);
		preOrderTraversal(root.left);
		preOrderTraversal(root.right);
	}
	public static void inOrderTraversal(Node root) {
		//Sequential traversal
		//Mid-order traversal of left subtree + root + right subtree
		if(root==null) {
			return ;
		}
		inOrderTraversal(root.left);
		System.out.println(root);
		inOrderTraversal(root.right);
	}
	public static void postOrderTraversal(Node root) {
		//Follow-up traversal of binary trees
		if(root==null) {
			return;
		}
		postOrderTraversal(root.left);
		postOrderTraversal(root.right);
		System.out.println(root);
        public static void main(String[] args) {
		Node root=buildTree();	
		System.out.println("Succcess");
		preOrderTraversal(root);
		System.out.println("====================");
		inOrderTraversal(root);
		System.out.println("=====================");
		postOrderTraversal(root);
		System.out.println("=====================");
	}