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Common Java Interview Questions

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Java and C++

  1. Compare C++ to Java.
    2. Some of the similarities and differences are in the table:
    Features Java C/C++
    Pointer No Yes
    Operator Overload No Yes
    Typedef, Define, Preprocessors No Yes
    Structures, Unions No Yes
    Enums No Yes
    Functions No (only methods within classes) Yes
    Goto statement No Yes
    Automatic Coercions No(types should be converted explicitly) Yes
    Global Variables No. Variable is part of a class Yes
    Templates No Yes
    Private, Protected, Public Inheritance No Yes
    Default parameters No Yes
    Garbage Collection Yes No
    Multi-thread support Yes No
    Multiple Inheritance Yes. Supports only interface inheritance and
    not implementation inheritance!    		 Yes
    Exception Handling Yes. try/catch must be defined if the function declares that it may throw an exception. Yes. You may not include the try/catch even if the function throws an exception.
    Function Overload Yes Yes
    Internationalization Yes Yes
    Include of other Objects #import #include
    Comments "//","/* */,/** */ "//","/* */"

Basic concepts

  1. What is it object serialization ?
    2. Serialization is a way to convert objects (including complex data structures such as lists and trees) into a stream of bytes.
  2. What is it reflection (introspection) ? Why is reflection possible in the Java language?
    3. Reflection (introspection) is querying a class about its properties, and operating on methods and fields by the name for a given object instance. Reflection is possible in the Java language because of late binding.
  3. How do I synchronize a block of code without declaring the entire method synchronized?
    4. One should use something like synchronized(this){...}
  4. Can you synchronize a block of code within a static method?
    5. Of course. You should write something like that: 
    class C
{
   static char[] x = new int[5];
   static void setX(int i, char value)
   {
      synchronized(x)
      {
         x[i] = value;
      }
   }
}
  5. What are the four member access level for Java?
    6. public,private,protected,package.

User interface

  1. What is the purpose of the toolkit in the Abstract Window Toolkit (AWT)? How does AWT work ?
    2. The AWT toolkit is an interface between the abstract window layer and a specific windowing implementation.
  2. What is layout manager ? How does it work ?
    3. A layout manager is an object that positions and resizes the components in a Container according to some algorithm; for example, the FlowLayout layout manager lays out components from left to right until it runs out of room and then continues laying out components below that row.
  3. Advantages and disadvantages of layout manager?
    4. The biggest advantage is the standard way of implementing the user interface for cross-platform application. Disadvantages are:
    - Challenge to create a custom layout if the standard one does not fit in your model
    - Inability to use native UI features of concrete operating system that might be quite useful especially for complex UI tasks (however, this is against the Java philosophy and quite understandable drawback)
  4. Compare SWING components to standard AWT.
    5. Swing is an extension of, and not a replacement for the AWT. There is some overlap between AWT and Swing (for example a Swing JButton component might be viewed as an improved functional replacement for an AWT Button component.) One of the advantages of Swing components is that because the components are not rendered on the screen by the operating system, the look and feel of a component does not change as the application or applet is executed on different platforms running under different operating systems. Furthermore, it is possible to cause Swing components to mimic the look and feel of a specific platform no matter what platform the program is running on. This is known as pluggable look and feel. Swing components support the JDK 1.1 Delegation Event Model. From an event handling viewpoint, Swing components operate the same as AWT components (except that Swing provides a number of new event types). Many Swing components don't have an AWT counterpart. A number of new and exciting components are included in the Swing library that don't exist in the AWT (tooltips, progress bars, trees, etc.)

Java Beans

  1. What is Java Beans ?
    2. According to JavaSoft, "A Java Bean is a reusable software component that can be manipulated visually in a builder tool."

Networking

  1. What you know about Corba implementation in Java?
    2. Java 1.2 promises full CORBA IDL support.
  2. What do you know about networking support in Java?
    3. Java supports "low-level" and "high-level" classes. "Low-level" classes provide support for socket programming: Socket, DatagramSocket, and ServerSocket classes. "High-level" classes provide "Web programming": URL, URLEncoder, and URLConnection classes. Networking programming classes ease the programming of network applications, but do not substitute your knowledge of networking. Java networking like anything else in Java is platform-independent.

Threads

  1. How to make application thread-safe ?
    2. You should use the word synchronized to mark the critical section of code. You may also use other methods of thread synchronization (see wait(), notify(), notifyAll() etc.

Deployment

  1. Why are Java ARchive (JAR) files important?
    2. JAR files bundle .class files and optimize applet downloads.