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Java Online Compiler

Write and run Java in your browser

Practise the coding round of an automation interview without installing a JDK. Write the program, press Run inside the editor, and read the output – free and no login.

Java editor

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The programs asked in automation interviews

Write each one from memory, then check it here. These come up again and again for 1–5 year automation roles.

Strings

  • Reverse a string without reverse()
  • Check a palindrome
  • Count duplicate characters with a HashMap
  • Count vowels and consonants
  • Reverse the words in a sentence
  • Check whether two strings are anagrams

Arrays and collections

  • Second highest number in one pass
  • Remove duplicates from an array
  • Sort a list of objects with a Comparator
  • Find a missing number in a sequence
  • HashMap vs Hashtable – show the null-key difference

Logic

  • Fibonacci series and factorial
  • Prime numbers up to N
  • Swap two numbers without a third variable
  • Sum of digits of a number

Java 8

  • Filter a list with a stream
  • Group a list with Collectors.groupingBy
  • Sort a map by value
  • Find the first non-repeating character with a stream
Java interview questions Automation study notes

Why Java matters for a tester

  • Selenium, TestNG, Rest Assured, Cucumber and Appium are all driven from Java in most Indian product and service companies
  • Every automation interview has a coding round, and it is usually string or collection logic
  • Reading a framework someone else wrote is a Java skill before it is a Selenium skill
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