155 Java Interview Questions
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OOPS
Q.1 What is an Object?
Q.2 What is a Class?
Q.3 What is OOAD?
Q.4 What is Data Abstraction ?
Q.5 What is Data Encapsulation?
Q.6 What is the difference between Data Abstraction and Information Hiding?
Q.7 What is Inheritance and what are different types of it?
Q.8 Why Java uses Singly rooted hierarchy?
Q.9 Why does Java not support Multiple Inheritance?
Q.10 Why is Java not 100% pure OOP language?
Q.11 What is Early Binding?
Q.12 What is Polymorphism/Late Binding?
Q.13 What is method overloading?
Q.14 What is method overriding?
Q.15 How is Java different from C++?
Q.16 What is UML and how is it useful in designing large systems?
Q.17 Is UML useful for procedural programming ?
Q.18 What are different notations used in UML ?
Q.19 What is a Use case and an Actor?
Q.20 How to identify an Actor?
Q.21 What is Generalization?
Q.22 What is Association and how it maps into a Java class?
Q.23 What is Aggregation and how it maps into a Java class?
Q.24 What is Composition and how it maps into a Java class?
Q.25 What is Dependency and how it maps into a Java class?
Q.26 What is the purpose of State machine diagrams?
Q.27 What are different kinds of Structure diagrams?
Q.28 What are different kinds of Interaction diagrams?
Q.29 What are different kinds of Behavior diagrams?
Java Fundamentals
Q.30 What is a Java Virtual Machine (JVM)?
Q.31 What is a JVM consisted of?
Q.32 What is a class loader and what is its responsibilities?
Q.33 What is heap and stack?
Q.34 How is your Java program executed inside JVM?
Q.35 What is Java class file's magic number?
Q.36 How JVM performs Thread Synchronization?
Q.37 How JVM performs Garbage Collection?
Q.38 How to profile heap usage?
Q.39 What will you do if VM exits while printing "OutOfMemoryError" and increasing max heap size doesn't help?
Q.40 Should one pool objects to help Garbage Collector?Should one call System.gc() periodically?
Q.41 An application has a lot of threads and is running out of memory, why?
Q.42 If your program is I/O bound or running in native methods, do these activities engage JVM?
Q.43 What is the difference between interpreted code and compiled code?
Q.44 Why Java based GUI intensive program has performance issues?
Q.45 What is 64 bit Java ?
Q.46 What is the difference between JVM and JRE?
Q.47 What are different primitive datatypes in Java?
Q.48 What are expressions,statements and blocks in Java?
Q.49 What is a transient variable?
Q.50 What is the difference between the '&' operator and the '&&' operator?<
Q.51 Why main method of Java has public static void?
Q.52 If you have static block, constructor and main method in Java file then what will be the sequence of method calls?
Q.53 What are the command line arguments?
Q.54 Does Java support multi dimensional arrays?
Q.55 What are the restrictions for static method?
Q.56 Why a abstract method cannot be static?
Q.57 Is 'sizeof' a keyword?
Q.58 What is the precedence of operators in Java?
Q.59 How is an argument passed in Java methods?
Q.60 What is the difference between class variable, member variable and automatic(local) variable?
Q.61 When are static and non static variables of a class initialized?
Q.62 Can shift operators be applied to float types?
Q.63 What are different Java declarations and their associated rules?
Q.64 What are Java Modifiers?
Q.65 Explain final modifier?
Q.66 Can you change the reference of the final object?
Q.67 Can abstract class be instantiated?
Q.68 When does the compiler insist that the class must be abstract?
Q.69 Where can static modifiers be used?
Q.70 What is static initializer code?
Q.71 Can an anonymous class implement an interface and extend a class at the same time?
Q.72 What are volatile variables?
Q.73 Can protected or friendly features be accessed from different packages?
Q.74 How many ways can one write an infinite loop?
Q.75 When do you use 'continue' and 'break' statements?
Q.76 What is the difference between 'while' and 'do while' loop?
Q.77 What is an Assertion and why using assertion in your program is a good idea ?
Q.78 Explain Assertions with a code exmaple.
Q.79 How many forms of assertions we have?
Q.80 When assertions should be avoided?
Q.81 What situations are best suitable for implementing assertions?
Q.82 What is Exception ?
Q.83 What is a user-defined exception?
Q.84 What do you know about the garbage collector?
Q.85 Why Java does not support pointers?
Q.86 Does garbage collection guarantee that a program will not run out of memory?
Q.87 What is finally in Exception handling?
Q.88 What can prevent the execution of the code in finally block?
Q.89 Explain 'try','catch' and 'finally' blocks?
Q.90 Define Checked and Unchecked exception?
Q.91 What is the difference between an abstract class and an interface?
Q.92 What is the use of interface?
Q.93 What is serializable interface?
Q.94 Does a class inherit constructors from its superclass?
Q.95 What's the difference between constructors and other methods?
Q.96 If the method to be overridden has access type 'protected', can subclass have the access type as 'private'?
Q.97 If you use super() or this() in a constructor where should it appear in the constructor?
Q.98 What modifiers may be used with an inner class that is a member of an outer class?
Q.99 Can an inner class be defined inside a method?
Q.100 What is an anonymous class?
Q.101 What is a thread?
Q.102 What is the difference between process and threads?
Q.103 What are two types of multitasking?
Q.104 What are two ways of creating threads in Java and why so?
Q.105 How does multithreading take place on a computer with a single CPU?
Q.106 How a Java object be locked for exclusive use by a given thread?
Q.107 What is Synchronization?
Q.108 Explain wait(),notify(), and notifyAll() methods?
Q.109 What is a Daemon thread?
Q.110 How a dead thread can be started?
Q.111 What is the difference between String and StringBuffer?
Q.112 How is '==' different from .equals() method in case of String objects?
Q.113 Explain StreamTokenizer?
Q.114 What is Collection?
Q.115 Explain List,Set and Map.
Q.116 What is the serialization?
Q.117 What is the difference between Serializable and Externalizable interface?
Q.118 What is memory leak?
Q.119 Difference between ArrayList and Vector class?
Q.120 What is the difference between Hashtable and HashMap?
Q.121 What is JFC?
Q.122 What is the difference between JFC Swing and AWT?
Q.123 What is the base class for all swing components?
Q.124 What are lightweight and heavyweight components ?
Q.125 How can a GUI component handle its own events?
Q.126 What is a Layout Manager and what are its different types and their advantages?
Q,127 How are the elements of a GridBagLayout organized?
Q.128 What are the problems faced by Java programmers in absence of layout managers?
Q.129 Where the CardLayout is used?
Q.130 What is the difference between GridLayout and GridBagLayout?
Q.131 How will you add a panel to a frame?
Q.132 What is the difference between Application and Applet?
Q.133 Explain Lifecycle of the Applet and what is the order of method invocation in an applet?
Q.134 What is the difference between Java class and bean?
Q.135 What is difference between trusted and untrusted applet?
Q.136 How do you set Java Library path programmatically?(new)
Q.137 Explain the usage of java.util.Date and more classes and APIs for date handling in Java?(new)
JDBC
Q.138 What is JDBC ?
Q.139 What are four drivers available in JDBC?
Q.140 How do you establish database connection using JDBC?
Q.141 What are the different types of Statements?
Q.142 What is PreparedStatement and how is different from Statement?
Q.143 What is the difference between executeQuery () and execute() ?
Q.144 What is the difference between executeQuery () and executeUpdate()?
Q.145 How do you call a stored procedure in Java?
Q.146 What are new features from JDBC2.0 onwards?
Q.147 How can a cursor move in scrollable result sets?
Q.148 Differentiate TYPE_SCROLL_INSENSITIVE and TYPE_SCROLL_SENSITIVE?
Q.149 How will you differentiate the following two ways of loading a database driver?
Q.150 How can you display a particular web page from an applet?(new)
Q.151 How can you get the hostname on the basis of IP addres ?(new)
Q.152 How can you get an IP address of a machine from its hostname?(new)
Q.153 How do you know who is accessing your server?(new)
Q.154 What are different socket options?(new)
Q.155 What should I use a ServerSocket or DatagramSocket in my applications?(new)
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