Explanation of Top Ten classes in java

  1. java.lang.String
    String class will be the undisputed champion on any day by popularity and none will deny that. This is a final class and used to create / operate immutable string literals. It was available from JDK 1.0
  2. java.lang.System
    Usage of System depends on the type of project you work on. You may not be using it in your project but still it is one of the popular java classes around. This is a utility class and cannot be instantiated. Main uses of this class are access to standard input, output, environment variables, etc. Available since JDK 1.0
  3. java.lang.Exception
    Throwable is the super class of all Errors and Exceptions. All abnormal conditions that can be handled comes under Exception. NullPointerException is the most popular among all the exceptions. Exception is at top of hierarchy of all such exceptions. Available since JDK 1.0
  4. java.util.ArrayList
    An implementation of array data structure. This class implements List interface and is the most popular member or java collections framework. Difference between ArrayList and Vector is one popular topic among the beginners and frequently asked question in java interviews. It was introduced in JDK 1.2
  5. java.util.HashMap
    An implementation of a key-value pair data structure. This class implements Map interface. As similar to ArrayList vs Vector, we have HashMap vs Hashtable popular comparisons. This happens to be a popular collection class that acts as a container for property-value pairs and works as a transport agent between multiple layers of an application. It was introduced in JDK 1.2
  6. java.lang.Object
    Great grandfather of all java classes. Every java class is a subclass of Object. It will be used often when we work on a platform/framework. It contains the important methods like equals, hashcode, clone, toString, etc. It is available from day one of java (JDK 1.0)
  7. java.lang.Thread
    A thread is a single sequence of execution, where multiple thread can co-exist and share resources. We can extend this Thread class and create our own threads. Using Runnable is also another option. Usage of this class depends on the domain of your application. It is not absolutely necessary to build a usual application. It was available from JDK 1.0
  8. java.lang.Class
    Class is a direct subclass of Object. There is no constructor in this class and their objects are loaded in JVM by classloaders. Most of us may not have used it directly but I think its an essential class. It is an important class in doing reflection. It is available from JDK 1.0
  9. java.util.Date
    This is used to work with date. Sometimes we feel that this class should have added more utility methods and we end up creating those. Every enterprise application we create has a date utility. Introduced in JDK 1.0 and later made huge changes in JDK1.1 by deprecating a whole lot of methods.
  10. java.util.Iterator
    This is an interface. It is very popular and came as a replacement for Enumeration. It is a simple to use convenience utility and works in sync with Iterable. It was introduced in JDK 1.2

Comments

Post a Comment

Please post comments here:-)

Popular posts from this blog

Android Objective type Question and Answers

Android Objective type Question and Answers 1) Once installed on a device, each Android application lives in_______?  a)device memory  b)external memory  c) security sandbox  d)None of the above Ans) c 2)Parent class of Activity?  a)Object  b)Context  c)ActivityGroup  d)ContextThemeWrapper Ans) d 3)What are the Direct subclasses of Activity?  a)AccountAuthenticatorActivity  b) ActivityGroup  c) ExpandableListActivity  d) FragmentActivity  e) ListActivity  f) all the aove Ans) f 4)What are the indirect Direct subclasses of Activity?  a)LauncherActivity  b)PreferenceActivity  c) TabActivity  d)All the above Ans) d 5)Parent class of Service?  a)Object  b)Context  c) ContextWrapper  d)ContextThemeWrapper Ans) c 6)What are the indirect Direct subclasses of Services?  a) RecognitionService  b) RemoteViewsService  c)SpellCheckerS...
Read more

Android Questions and Answers for written exams

1. bmgr tool is used to a)take backup of the applications b)to restore operations c)wipe archived data for a specific application d)all of the above ans: d 2. foreground service a)starts when you call start foreground() b)may or may not provide a notification for the status bar c)notification can't be dismissed unless the service is either stopped or removed from the foreground d)both a & c ans:d 3. A1,A2,A3 and A4 are activities called using intents.Then A1-A4-A2--A3.A4 calls A2 with intent flag FLAG_ACTIVITY_NO_HISTORY.When finish method is called on A3, What will be the currtent running activity? a)A1 b)A4 c)A3 d)A2 ans: b 4. A1,A2,A3 and A4 are activities called using intents.Then A1-A2-A4--A3.A2 calls A4 with intent flag FLAG_ACTIVITY_CLEAR_TOP.When finish() method is called on A3, what will be the current running activity? a)A4 b)A3 c)A2 d)A1 Ans:  a 5. A1,A2,A3 and A4 are activities called using intents.Then A1-A2-A3-A4. A3 call...
Read more

SCJP1.6 Question and Answers

Question – 1 What is the output for the below code ? 1.         public class A { 2.         int add(int i, int j){ 3.                     return i+j; 4.                     } 5.         } 6.         public class B extends A{ 7.         public static void main(String argv[]){ 8.         short s = 9; 9.         System.out.println(add(s,6)); 10.        } 11.        } Options are A. Compile fail due to error on line no 2 B. Compile fail due to error on lin...
Read more