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Top 165 Java Interview Questions
Entry Junior Mid Senior Expert
Theoretical Questions
Q1:
What is JVM? Why is Java called the "Platform Independent Programming Language”?
Entry
Q2:
What is the difference between an Applet and a Java Application?
Entry
Q3:
What are the two types of Exceptions in Java? Which are the differences between them?
Entry
Q4:
What is a JSP Page?
Entry
Q5:
What is a Servlet?
Entry
Q6:
What is the Difference between JDK and JRE?
Entry
Q7:
What is an Iterator?
Junior
Q8:
What are the Data Types supported by Java? What is Autoboxing and Unboxing?
Junior
Q9:
What are the basic interfaces of Java Collections Framework?
Junior
Q10:
How HashMap works in Java?
HashMap works in Java? Junior
Q11:
What is an Java Applet?
Junior
Q12:
What are pass by reference and pass by value?
Junior
Q13:
What is the difference between processes and threads?
Junior
Q14:
When does an Object becomes eligible for Garbage Collection in Java ?
Object becomes eligible for Garbage Collection in Java ? Junior
Q15:
What is the difference between Exception and Error in Java?
Exception and Error in Java? Junior
Q16:
What is the importance of finally block in exception handling?
finally block in exception handling? Junior
Q17:
What does the static keyword mean? Can you override private or static method in Java?
static keyword mean? Can you override private or static method in Java? Junior
Q18:
What is JDBC?
Junior
Q19:
What is the purpose of Garbage Collection in Java, and when is it used?
Junior
Q20:
How does Garbage Collection prevent a Java application from going out of memory?
Junior
Q21:
Explain Serialization and Deserialization.
Junior
Q22:
Explain the architechure of a Servlet.
Junior
Q23:
What is reflection and why is it useful?
Junior
Q24:
What are JSP Actions?
Junior
Q25:
What are Decalarations?
Junior
Q26:
What’s the difference between sendRedirect and forward methods?
sendRedirect and forward methods? Junior
Q27:
What is the purpose Class.forName method?
Class.forName method? Junior
Q28:
What is the design pattern that Java uses for all Swing components?
Junior
Q29:
How are the JSP requests handled?
Junior
Q30:
What is Function Overriding and Overloading in Java?
Junior
Q31:
What do you know about the Big-O notation and can you give some examples with respect to different data structures?
Junior
Q32:
What are Expressions?
Junior
Q33:
What is the difference between an Interface and an Abstract class?
Interface and an Abstract class? Junior
Q34:
What will happen to the Exception object after exception handling?
Exception object after exception handling? Junior
Junior
Q36:
What are Directives?
Junior
Q37:
What differences exist between HashMap and Hashtable?
HashMap and Hashtable? Junior
Q38:
What does System.gc() and Runtime.gc() methods do?
System.gc() and Runtime.gc() methods do? Junior
Q39:
What is difference between fail-fast and fail-safe?
Mid Q40:
Compare the sleep() and wait() methods in Java
sleep() and wait() methods in Java Mid Q41:
Is there anything like static class in Java?
static class in Java? Mid Q42:
What are the differences between == and equals?
== and equals? Mid Q43:
How threadsafe is enum in Java?
enum in Java? Mid Q44:
What is meant by JSP implicit objects and what are they?
Mid Q45:
What is the advantage of PreparedStatement over Statement?
PreparedStatement over Statement? Mid Q46:
What is difference between Array and ArrayList? When will you use Array over ArrayList?
Array and ArrayList? When will you use Array over ArrayList? Mid Q47:
What is the main difference between StringBuffer and StringBuilder?
StringBuffer and StringBuilder? Mid Q48:
What is Java Priority Queue?
Mid Q49:
Explain different ways of creating a thread. Which one would you prefer and why?
Mid Q50:
What is the importance of hashCode() and equals() methods?
hashCode() and equals() methods? Mid Q51:
What is the volatile keyword useful for?
volatile keyword useful for? Mid Q52:
Can == be used on enum?
== be used on enum? Mid Q53:
What do the ... dots in the method parameters mean?
... dots in the method parameters mean? Mid Q54:
Why does Java have transient fields?
Mid Q55:
Is Java pass-by-reference or pass-by-value?
Mid Q56:
What is static initializer?
Mid Q57:
What's the advantage of using getters and setters?
Mid Q58:
What is the difference between public, protected, package-private and private in Java?
public, protected, package-private and private in Java? Mid Q59:
What is the difference between HashMap, LinkedHashMap and TreeMap in Java?
HashMap, LinkedHashMap and TreeMap in Java? Mid Q60:
How and where are Annotations used in Java?
Mid Q61:
What is the Java Classloader?
Mid Q62:
Can an enum be extended?
enum be extended? Mid Q63:
What is a JavaBean exactly?
Mid Q64:
What is the JIT?
Mid Q65:
What are the advantages of JSP?
Mid Q66:
How do I break out of nested loops in Java?
Mid Q67:
How can I synchornize two Java processes?
Mid Q68:
What’s the difference between a ClassNotFoundException and NoClassDefFoundError?
ClassNotFoundException and NoClassDefFoundError? Mid Q69:
Can you access non static variable in static context?
Mid Q70:
What is the difference between final, finalize and finally?
final, finalize and finally? Mid Q71:
What are the restrictions imposed on Java applets?
Mid Q72:
What is the role of stub in RMI?
stub in RMI? Mid Q73:
What is the difference between GenericServlet and HttpServlet?
GenericServlet and HttpServlet? Mid Q74:
What are Scriptlets?
Mid Q75:
Explain the life cycle of an Applet.
Mid Q76:
Explain the life cycle of a Servlet.
Mid Q77:
Which Swing methods are thread-safe?
Mid Q78:
What’s a deadlock?
Mid Q79:
What is the tradeoff between using an unordered array versus an ordered array?
Mid Q80:
What is the difference between doGet() and doPost()?
doGet() and doPost()? Mid Q81:
What is structure of Java Heap?
Heap? Mid Q82:
What differences exist between Iterator and ListIterator?
Iterator and ListIterator? Mid Q83:
How does finally block differ from finalize() method?
finally block differ from finalize() method? Mid Q84:
Explain the role of Driver in JDBC.
Mid Q85:
What is the difference between throw and throws?
throw and throws? Mid Q86:
What is Comparable and Comparator interface? List their differences.
Comparable and Comparator interface? List their differences. Mid Q87:
What are untrusted applets?
Mid Q88:
What is difference between ArrayList and LinkedList?
ArrayList and LinkedList? Mid Q89:
What is the difference between an Applet and a Servlet?
Mid Q90:
What are the steps involved to make work a RMI program?
Mid Q91:
Why Collection doesn’t extend Cloneable and Serializable interfaces?
Cloneable and Serializable interfaces? Mid Q92:
If an object reference is set to null, will the Garbage Collector immediately free the memory held by that object?
null, will the Garbage Collector immediately free the memory held by that object? Mid Q93:
What is a Constructor, Constructor Overloading and Copy-Constructor in Java ?
Mid Q94:
What’s the difference between Enumeration and Iterator interfaces?
Enumeration and Iterator interfaces? Mid Q95:
What is a Server Side Include (SSI)?
Mid Q96:
Does Java support multiple inheritance?
Mid Q97:
What is the relationship between an event-listener interface and an event-adapter class?
Mid Q98:
What is the applet security manager, and what does it provide?
Mid Q99:
What happens when an Applet is loaded?
Mid Q100:
When is the finalize() called? What is the purpose of finalization?
finalize() called? What is the purpose of finalization? Mid Q101:
What are some of the best practices relating to the Java Collection Framework?
Senior Q102:
Why is char[] preferred over String for passwords?
char[] preferred over String for passwords? Senior Q103:
What are the differences between a HashMap and a HashTable in Java?
HashMap and a HashTable in Java? Senior Q104:
What exactly is marker interface in Java?
marker interface in Java? Senior Q105:
When to use LinkedList over ArrayList in Java?
LinkedList over ArrayList in Java? Senior Q106:
Why is Spring MVC better than Servlets / JSP ?
Senior Q107:
Explain a use case for the Builder Design Pattern
Senior Q108:
What is the difference between Applets loaded over the internet and Applets loaded via the file system?
Senior Q109:
How do you ensure that N threads can access N resources without deadlock?
N threads can access N resources without deadlock? Senior Q110:
Does Java support default parameter values?
Senior Q111:
What is the purpose of using RMISecurityManager in RMI?
Senior Q112:
What is the role of the java.rmi.Naming Class?
java.rmi.Naming Class? Senior Q113:
What is the main difference between an inner class and a static nested class in Java?
Senior Senior Senior Q116:
What is Servlet Chaining?
Senior Q117:
What is the basic principle of RMI architecture?
Senior Q118:
What does Connection Pooling mean?
Senior Q119:
What is meant by binding in RMI?
Senior Q120:
How do you find out what client machine is making a request to your servlet?
Senior Q121:
Explain Marshalling and Demarshalling.
Senior Q122:
What is the applet class loader, and what does it provide?
Senior Q123:
What is the difference between a synchronized method and a synchronized block?
Senior Q124:
What is Double Brace initialization in Java?
Senior Q125:
How do I test a private function or a class that has private methods, fields or inner classes?
Senior Q126:
What is Perm Gen space in Heap?
Heap? Senior Q127:
What is the difference between Serial and Throughput Garbage collector?
Senior Q128:
Explain the available thread states in a high-level.
Senior Q129:
What is the role of Remote Interface in RMI?
Senior Q130:
What is RMI?
Senior Q131:
Does Garbage collection occur in permanent generation space in JVM?
Expert Q132:
What does synchronized mean?
synchronized mean? Expert Q133:
What are the layers of RMI Architecture?
Expert Q134:
What is DGC? And how does it work?
Expert Q135:
What is the difference between HashSet and TreeSet?
HashSet and TreeSet? Expert Q136:
What's wrong with Double Brace Initialization in Java?
Expert Q137:
How does thread synchronization occurs inside a monitor? What levels of synchronization can you apply?
monitor? What levels of synchronization can you apply? Expert Q138:
Why isn’t String‘s length() accurate?
length() accurate? Expert Q139:
Provide some examples when a finally block won't be executed in Java?
finally block won't be executed in Java? Expert Q140:
Compare volatile vs static variables in Java
volatile vs static variables in Java Expert Q141:
Why ArrayList are preferable in many more use-cases than LinkedList?
ArrayList are preferable in many more use-cases than LinkedList? Expert Q142:
What's the difference between SoftReference and WeakReference in Java?
SoftReference and WeakReference in Java? Expert Q143:
What is an efficient way to implement a singleton pattern in Java?
Expert Code Challenges
Q1:
How do I efficiently iterate over each entry in a Java Map?
Map?
Junior Q2:
JSJavaPY Related To: Fibonacci Series, Data Structures, JavaScript
Return the N-th value of the Fibonacci sequence Recursively
JSJavaPY Related To: Fibonacci Series, Data Structures, JavaScript Junior Junior Junior Junior Q6:
JSJavaPY Related To: Arrays, Data Structures, JavaScript, Python
How to merge two sorted Arrays into a Sorted Array?
JSJavaPY Related To: Arrays, Data Structures, JavaScript, Python Mid Q7:
CSJavaPY Related To: Strings, Data Structures, C#
How to check if two Strings (words) are Anagrams?
CSJavaPY Related To: Strings, Data Structures, C# Mid Mid Q9:
JSJavaPY Related To: Backtracking, Strings, Data Structures, Python, JavaScript
Find all the Permutations of a String
JSJavaPY Related To: Backtracking, Strings, Data Structures, Python, JavaScript Mid Mid Q12:
How do I read/convert an InputStream into a String in Java?
InputStream into a String in Java? Mid Q13:
Java Related To: Linked Lists
Floyd's Cycle Detect Algorithm: Explain how to find a starting node of a Cycle in a Linked List?
Java Related To: Linked Lists Mid Q14:
What is the use of CallableStatement? Name the method, which is used to prepare a CallableStatement.
CallableStatement? Name the method, which is used to prepare a CallableStatement. Mid Q15:
Is it possible to call one constructor from another in Java?
Senior Q16:
Given two double values d1, d2, what is the most reliable way to test their equality?
d1, d2, what is the most reliable way to test their equality? Senior Senior Q18:
Is null check needed before calling instanceof?
null check needed before calling instanceof? Senior Q19:
JavaPY Related To: Fibonacci Series, Matrices
Get Fibonacci Number in O(log n) time using Matrix Exponentiation
JavaPY Related To: Fibonacci Series, MatricesO(log n) time using Matrix Exponentiation Senior Q20:
JavaPY Related To: Linked Lists, Python
Given a singly Linked List, determine if it is a Palindrome
JavaPY Related To: Linked Lists, Python Senior Expert Q22:
Explain what will the code return
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