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Core Java Interview Question And Answer for Freshers

Click here -    / @interviewdot   to get notifications. Core Java Interview Question And Answer for Freshers www.InterviewDot.com - Job Portal Java Interview Questions And Answers For Freshers 1.What is the difference between HashMap and Hashtable class ? Hashtable HashMap Hashtable class is synchronize. HastMap is not synchronize. Because of Thread-safe, HashMap works faster. Hashtable is slower than HashMap Neither key nor values can be null Both key and values can be null Order of table remain constant over time. Does not guarantee that order of map remain constant over time. 2.What is the difference between ArrayList and Vector class ? Vector ArrayList Vector class is synchronize. ArrayList is not synchronize. Because of Thread-safe, Vector is slower than ArrayList ArrayList works faster. Enumeration is used to iterate through the element of Vector. Iterator is used to iterate through the element of ArrayList. 3.Why String is immutable in Java ? In Java, strings are object. There are many different ways to create a String object. One of them is using string literals. Each time a string literal is created, JVM checks the string constant pool first. If string already exist in the pool, a reference to the pool instance is returned. Sometime it is possible that one string literals is referenced by many reference variable. So if any of them change the string, other will also get affected. This is the prominent reason why string object is immutable. String str1 = "hello" String str2 = "hello" str1 == str2 4.Difference between StringBuffer and StringBuilder ? Both StringBuffer and StringBuilder classes are almost same except for two major differences. StringBuffer StringBuilder StringBuffer is synchronize. StringBuoder is not synchronize. Because of synchronisation, StringBuilder operates faster. StringBuffer operation is slower than StringBuilder. 5.Difference between equals() method and == operator ? Main difference between '==' and equals() in Java is that '==' is a operator used to check whether two different reference refers to same instance and equals() is a method used to check equality of an object. Another important difference is '==' operators is used more with primitive data type while equals() method is used for object. 6.What are the different ways to create a thread in java ? There are two different way to create a thread in java. 1. Extending Thread class. yourclass extends Thread 2. By implementing Runnable interface. 7.What are the difference between sleep() and wait() method. wait() method in java should be called from synchronized block while there is no such requirement for sleep() method. Another difference is sleep() method is a static method, while wait() is an instance specific method called on thread object. In case of sleep(), sleeping thread immediately goes to Runnable state after waking up while in case of wait(), waiting thread first acquires the lock and then goes into Runnable state. notify() and notifyAll of Object class are used to awake a waiting Thread while sleeping thread can not be awaken by calling notify() method. wait() method is defined in Object class while sleep() is defined in Thread class. 8.What is serialization in java ? Serialization is a process of converting object into a sequences of byte which can be written to disk or database or sent over network to any other running JVM. The reverse process of creating object from sequences of byte is called Deserialization. 9.What do you understand by Synchronization ? Synchronization is a process of controlling the access of shared resources by the multiple threads in such a manner that only one thread can access one resource at a time. In non synchronized multithreaded application, it is possible for one thread to modify a shared object while another thread is in the process of using or updating the object's value. 10.What is static in Java ? Static variables ,Static methods belongs to class and not to an object / instance. A Job Portal http://www.InterviewDot.com http://www.InterviewDot.com http://www.InterviewDot.com One Click Dream Job - http://www.interviewdot.com/upload-re... Other Top Job Portals www.Naukri.com www.MonsterIndia.com www.TimesJobs.com Are you looking for a new Job ? InterviewDot.com - A Job Portal http://www.InterviewDot.com http://www.InterviewDot.com http://www.InterviewDot.com One Click Dream Job - http://www.interviewdot.com/upload-re...