In the previous post entitled Java Tree structure interview questions and coding questions — Part 1, we looked at a very simple Tree structure. In this example, let’s look at a more complex tree structure with generics. Q. Write classes for a Tripple tree structue as shown below? … Read...
Q. What is wrong with the following code snippet?
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import java.util.HashMap; import java.util.Map; import java.util.concurrent.ExecutorService; import java.util.concurrent.Executors; import java.util.concurrent.TimeUnit; public class WhatIsWrong implements Runnable { //shared by threads final static Map<String, String> map = new HashMap<String, String>(); public static void main(String[] args) throws InterruptedException { ExecutorService pool = Executors.newFixedThreadPool(100); for (int i = 0; i < 100; i++) { WhatIsWrong wiw = new WhatIsWrong(); pool.submit(wiw); } pool.shutdown(); pool.awaitTermination(Long.MAX_VALUE, TimeUnit.MILLISECONDS); } @Override public void run() { for (int i = 0; i < 1000000; i++) { map.put(Thread.currentThread().getName(), "wow-" + i); Object retrieved = map.get(Thread.currentThread().getName()); if(retrieved == null) { System.out.println("Race conmdition detected!!! Map is in inconsistent state"); } } } } |
A. It is NOT thread-safe as a “HashMap” is not thread-safe as per the Java API, and race conditions can leave the “map” in “inconsistent state“. … Read more ›...
List, Set, Map, and Queue(access the ends FIFO or LIFO) are the basic Java data structure interfaces for which there are different implementations to cater for different usage patterns. Java data structure interview questions are very popular, … Read more ›...
The scenario based questions are very popular with the job interviewers, and some scenario based questions are related to decoupling and asynchronous (aka non-blocking) processing in Java with message queues/topics, database tables where one process inserts data and another process consumes the inserted data, and Future objects in Java multi-threading....
Step 1: Setup Java, Maven, and SonarQube
1. Java: Latest possible version. Setting up Java, Maven, and eclipse.
2. Maven 3: For building. Setting up Java, Maven, and eclipse.
3. SonarQube: For code quality.
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A distributed system consists of multiple software components that are on multiple computers (aka nodes), but run as a single system. These components can be stateful, stateless, or serverless, and these components can be created in different languages running on hybrid environments, using open-source technologies, open standards, and interoperability.
Q01.
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Q01. Can you describe a business domain of a Telecom company offering multiple services to its customers? A01. A Telecom company will have entities such as Customer, Account, Subscriptions & Products representing a business domain. 1) Each customer entity has a name, … Read more ›...
Java Web Services interview Questions & Answers Links: 6 Java RESTful Web services Interview | 11 SOAP Web service interview | 5 JAXB interview Questions & Answers | Java Web Services interview Questions & Answers Q1. … Read more ›...
Q. Complete the method “Set getAllCombinations(String input) ” where input is any string and the method should return all possible combinations of a given string.
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import java.util.Collection; import java.util.Collections; import java.util.HashSet; import java.util.Set; public class WordPermutations { public static Set<String> getAllCombinations(String input) { throw new RuntimeException("Complete the given code"); } public static void main(String[] args) { Collection<String> words = getAllCombinations("abc"); for (String word : words) System.out.println(word); } } |
For example: “abc” will have a permutation of 3! … Read more ›...
JMockit offers a set of utility fields & methods for making argument matching more generic. This extends 09: JMockit interview Q&As & examples on matching of argument values 1) anyX fields like anyInt, anyBoolean, … Read more ›...
This is an extension to Java Tree structure interview and coding questions — Part 2, and adds functional programming and recursion. Step 1: The Tree interface with get( ) method that returns either a Triple tree or Leaf data. … Read more ›...
Example #1 Wiring JDBC Datasource
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@Configuration @ImportResource("application.yml") public class AppConfig { @Autowired private Environment environment; @Bean public DriverManagerDataSource datasource() { DriverManagerDataSource ds = new DriverManagerDataSource(); ds.setDriverClassName(environment.getRequiredProperty("spring.datasource.driver-class-name")); ds.setUrl(environment.getRequiredProperty("spring.datasource.url")); ds.setUsername(environment.getRequiredProperty("spring.datasource.username")); ds.setPassword(environment.getRequiredProperty("spring.datasource.password")); return ds; } } |
application.yml where the datasource properties are read from.
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############ # Datasource properties ############ spring: datasource: driver-class-name: com.sybase.jdbc4.jdbc.SybDataSource url: jdbc:sybase:Tds:mydbhost:5700/my_db username: user password: pwd |
Example #2 Wiring JDBC Datasource with JNDI
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@Configuration @ImportResource("application.yml") public class AppConfig { @Autowired private Environment environment; @Bean public DataSource dataSource() { final JndiDataSourceLookup jndiLookup = new JndiDataSourceLookup(); final String dataSourceJndi = environment.getRequiredProperty("spring.datasource.jndi"); return jndiLookup.getDataSource(dataSourceJndi); } } |
Example #3 Wiring the JPA persistence unit processors Callback interface for post-processing a JPA PersistenceUnitInfo. … Read more ›...
Q. What output is expected from the following code? What does it actually output?
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import java.util.Collections; import java.util.HashMap; import java.util.Iterator; import java.util.Map; import java.util.concurrent.ExecutorService; import java.util.concurrent.Executors; import java.util.concurrent.TimeUnit; public final class WhatIsWrong implements Runnable { private Map<String, Integer> myMap = null; public WhatIsWrong(Map<String, Integer> myMap) { this.myMap = myMap; } public static void main(String[] args) throws InterruptedException { long start = System.currentTimeMillis(); Map<String, Integer> myMap = Collections.synchronizedMap(new HashMap<String, Integer>()); for (int i = 1; i <= 10; i++) { myMap.put("Key-" + i, i); // 10 items in the map } // process 1 million times with 20 threads ExecutorService threadPool = Executors.newFixedThreadPool(20); for (int i = 1; i <= 1000000; i++) { WhatIsWrong wiw = new WhatIsWrong(myMap); threadPool.submit(wiw); //submit 1 million tasks to the thread pool } threadPool.shutdown(); threadPool.awaitTermination(60, TimeUnit.SECONDS); traverseAndPrint(myMap); long finish = System.currentTimeMillis(); System.out.println("Processed in " + (finish - start) + " ms"); } @Override public void run() { traverseAndUpdate(); } private void traverseAndUpdate() { Iterator<String> it = myMap.keySet().iterator(); while (it.hasNext()) { String key = it.next(); Integer newValue = this.myMap.get(key) + 1; myMap.put(key, newValue); } } private static void traverseAndPrint(Map<String, Integer> myMap) { Iterator<String> it = myMap.keySet().iterator(); while (it.hasNext()) { String key = it.next(); System.out.println(key + " = " + myMap.get(key)); } } } |
A. It is expected to output counts from 100,001 to 100,010, but actually the output will be as shown below missing counts. Output with missing counts
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Key-1 = 570087 Key-2 = 527793 Key-3 = 518048 Key-4 = 493989 Key-5 = 466364 Key-6 = 578612 Key-7 = 508259 Key-8 = 517953 Key-9 = 480131 Key-10 = 433976 Processed in 1777 ms |
Why does the output miss counts?… Read more...
