Here is java program to evaluate post fix expression using stack.

In this program, I am going to show the use of few string manipulation functions in java.

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In computer science, a stack or LIFO (last in, first out) is an abstract data type that serves as a collection of elements, with two principal operations: push adds an element to the collection; pop removes the last element that was added. (Via Wikipedia)

Here is java code for implementation of stack using linked list in java.

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A circular queue is an abstract data type that contains a collection of data which allows addition of data at the end of the queue and removal of data at the beginning of the queue. Circular queues have a fixed size.

Circular queue follows FIFO principle. Queue items are added at the rear end and the items are deleted at front end of the circular queue.

A doubly-linked list is a linked data structure that consists of a set of sequentially linked records called nodes. Each node contains two fields, called links, that are references to the previous and to the next node in the sequence of nodes.

The two node links allow traversal of the list in either direction. Here is java implementation of DLL.

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Binary search trees (BST), sometimes called ordered or sorted binary trees, are a class of data structures used to implement lookup tables and dynamic sets. They store data items, known as keys, and allow fast insertion and deletion of such keys, as well as checking whether a key is present in a tree.

The common properties of binary search trees are as follows:

• One node is designated the root of the tree.
• Each internal node contains a key and has two subtrees.
• The leaves (final nodes) of the tree contain no key. Leaves are commonly represented by a special leaf or nil symbol, a NULL pointer, etc.
• Each subtree is itself a binary search tree.
• The left subtree of a node contains only nodes with keys strictly less than the node’s key.
• The right subtree of a node contains only nodes with keys strictly greater than the node’s key.