I have been posting java programs on various topics such as Binary tree, LinkedList , String, Number, ArrayList, HashMap etc. So I am consolidating list of programs to create an index post. I will keep adding links to this post whenever I add any new program. These are frequently asked programs in interview. You can also go through top 50 java interview questions for interview questions.
Collections:

Collections interview questions and answers
How HashMap internally works in java
How to iterate over HashMap in java
How to Sort ArrayList based on attributes using Comparator in java
How to sort ArrayList based on attributes using Comparable in java
How to remove duplicates from list in java
How to iterate over ArrayList in java
LinkedList :

How to reverse a linked list in java
How to reverse a linked list in pairs
How to find middle element of linked list in java
How to detect a loop in linked list in java
Find start node of loop in linkedlist
How to find nth element from end of linked list
How to check if linked list is palindrome in java
Add two numbers represented by linked list in java
Binary tree :

Binary tree in java
Binary tree preorder traversal
Binary tree postorder traversal
Binary tree inorder traversal
Binary tree level order traversal
Binary tree spiral order traversal
Binary tree reverse level order traversal
Binary tree boundary traversal
Print leaf nodes of binary tree
Count leaf nodes in binary tree
get maximum element in binary tree
Print all paths from root to leaf in binary tree
Print vertical sum of binary tree in java
Get level of node in binary tree in java
Lowest common ancestor(LCA) in binary tree in java
Array :

Find missing number in an array
search an element in a sorted and rotated array in java
Find second largest number in array
Find number occurring odd number of times in array
Minimum numbers of platforms required for railway station in java
Find pair whose sum is closest to zero in array in java
Find pair whose sum is closest to X in array in java
Find all pairs of elements whose sum is equal to given number
Search element in row wise and column wise sorted matrix
Stock buy and sell to maximize profit.
Sorting :

How to implement merge sort in java
How to implement bubble sort in java
How to implement insertion sort in java
String :

How to reverse String in java
How to check if two Strings are angrams
Find length of String without using java inbuilt length method
Find all substrings of String in java
Find First non repeated character in a String
Java Program to check Palindrome String
Why String is immutable in java
Find duplicate characters in String
Number :

How to swap two numbers without using temporary variables
Java program to check prime number
Find prime factors of number in java
Java Program to check armstrong number
Fibonacci series program in java
Java Program to check Palindrome Number
Java Program to to find gcd and lcm of two numbers