Question: What are different types of inner classes ?
Answer: Inner classes nest within other classes. A normal class is a direct member of a package. Inner classes, which became available with Java 1.1, are four types
Static member classes - a static member class is a static member of a class. Like any other static method, a static member class has access to all static methods of the parent, or top-level, class.
Member Classes - a member class is also defined as a member of a class. Unlike the static variety, the member class is instance specific and has access to any and all methods and members, even the parent's this reference.
Local Classes - Local Classes declared within a block of code and these classes are visible only within the block.
Anonymous Classes - These type of classes does not have any name and its like a local class
Question: What are the uses of Serialization?
Answer: In some types of applications you have to write the code to serialize objects, but in many cases serialization is performed behind the scenes by various server-side containers.
These are some of the typical uses of serialization:
Question: what is a collection ?
Answer: Collection is a group of objects. java.util package provides important types of collections. There are two fundamental types of collections they are Collection and Map. Collection types hold a group of objects, Eg. Lists and Sets where as Map types hold group of objects as key, value pairs Eg. HashMap and Hashtable.
Question: For concatenation of strings, which method is good, StringBuffer or String ?
Answer: StringBuffer is faster than String for concatenation.
Question: What is Runnable interface ? Are there any other ways to make a java program as multithred java program?
Answer: There are two ways to create new kinds of threads:
- Define a new class that extends the Thread class
- Define a new class that implements the Runnable interface, and pass an object of that class to a Thread's constructor.
- An advantage of the second approach is that the new class can be a subclass of any class, not just of the Thread class.
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