58.
Question :How does an exception permeate through the code?
59. Question :What are the different ways to handle exceptions?
60. Question :What is the basic difference between the 2 approaches to exception handling. 1. try catch block and 2. specifying the candidate exceptions in the throws clause? When should you use which approach?
61. Question :Is it necessary that each try block must be followed by a catch block?
62. Question :If I write return at the end of the try block, will the finally block still execute?
63. Question :If I write System.exit (0); at the end of the try block, will the finally block still execute?
64. Question :How are Observer and Observable used?
65. Question :What is synchronization and why is it important?
66. Question :How does Java handle integer overflows and underflows?
67. Question :Does garbage collection guarantee that a program will not run out of memory?
68. Question :What is the difference between preemptive scheduling and time slicing?
69. Question :When a thread is created and started, what is its initial state?
70. Question :What is the purpose of finalization?
71. Question :What is the Locale class?
72. Question :What is the difference between a while statement and a do statement?
73. Question :What is the difference between static and non-static variables?
74. Question :How are this() and super() used with constructors?
75. Question :What are synchronized methods and synchronized statements?
76. Question :What is daemon thread and which method is used to create the daemon thread?
77. Question :Can applets communicate with each other?
An applet can also get references to all other applets on the same page using the getApplets() method of java.applet.AppletContext. Once you get the reference to an applet, you can communicate with it by using its public members
It is conceivable to have applets in different virtual machines that talk to a server somewhere on the Internet and store any data that needs to be serialized there. Then, when another applet needs this data, it could connect to this same server. Implementing this is non-trivial
78. Question :What are the steps in the JDBC connection?
Step 1 : Register the database driver by using : Class.forName(\" driver classs for that specific database\" ); Step 2 : Now create a database connection using : Connection con = DriverManager.getConnection(url,username,password); Step 3: Now Create a query using : Statement stmt = Connection.Statement(\"select * from TABLE NAME\"); Step 4 : Exceute the query : stmt.exceuteUpdate();
Answer :
An unhandled exception moves up the method stack in search of a matching When an exception is thrown from a code which is wrapped in a try block followed by one or more catch blocks, a search is made for matching catch block. If a matching type is found then that block will be invoked. If a matching type is not found then the exception moves up the method stack and reaches the caller method. Same procedure is repeated if the caller method is included in a try catch block. This process continues until a catch block handling the appropriate type of exception is found. If it does not find such a block then finally the program terminates59. Question :What are the different ways to handle exceptions?
Answer :
There are two ways to handle exceptions, 1. By wrapping the desired code in a try block followed by a catch block to catch the exceptions. and 2. List the desired exceptions in the throws clause of the method and let the caller of the method handle those exceptions60. Question :What is the basic difference between the 2 approaches to exception handling. 1. try catch block and 2. specifying the candidate exceptions in the throws clause? When should you use which approach?
Answer :
In the first approach as a programmer of the method, you urself are dealing with the exception. This is fine if you are in a best position to decide should be done in case of an exception. Whereas if it is not the responsibility of the method to deal with it's own exceptions, then do not use this approach. In this case use the second approach. In the second approach we are forcing the caller of the method to catch the exceptions, that the method is likely to throw. This is often the approach library creators use. They list the exception in the throws clause and we must catch them. You will find the same approach throughout the java libraries we use61. Question :Is it necessary that each try block must be followed by a catch block?
Answer :
It is not necessary that each try block must be followed by a catch block. It should be followed by either a catch block OR a finally block. And whatever exceptions are likely to be thrown should be declared in the throws clause of the method62. Question :If I write return at the end of the try block, will the finally block still execute?
Answer :
Yes even if you write return as the last statement in the try block and no exception occurs, the finally block will execute. The finally block will execute and then the control return63. Question :If I write System.exit (0); at the end of the try block, will the finally block still execute?
Answer :
No in this case the finally block will not execute because when you say System.exit (0); the control immediately goes out of the program, and thus finally never executes64. Question :How are Observer and Observable used?
Answer :
Objects that subclass the Observable class maintain a list of observers. When an Observable object is updated it invokes the update() method of each of its observers to notify the observers that it has changed state. The Observer interface is implemented by objects that observe Observable objects65. Question :What is synchronization and why is it important?
Answer :
With respect to multithreading, synchronization is the capability to control the access of multiple threads to shared resources. Without synchronization, it is possible for one thread to modify a shared object while another thread is in the process of using or updating that object's value. This often leads to significant errors66. Question :How does Java handle integer overflows and underflows?
Answer :
It uses those low order bytes of the result that can fit into the size of the type allowed by the operation67. Question :Does garbage collection guarantee that a program will not run out of memory?
Answer :
Garbage collection does not guarantee that a program will not run out of memory. It is possible for programs to use up memory resources faster than they are garbage collected. It is also possible for programs to create objects that are not subject to garbage collection68. Question :What is the difference between preemptive scheduling and time slicing?
Answer :
Under preemptive scheduling, the highest priority task executes until it enters the waiting or dead states or a higher priority task comes into existence. Under time slicing, a task executes for a predefined slice of time and then reenters the pool of ready tasks. The scheduler then determines which task should execute next, based on priority and other factors69. Question :When a thread is created and started, what is its initial state?
Answer :
A thread is in the ready state after it has been created and started70. Question :What is the purpose of finalization?
Answer :
The purpose of finalization is to give an unreachable object the opportunity to perform any cleanup processing before the object is garbage collected71. Question :What is the Locale class?
Answer :
The Locale class is used to tailor program output to the conventions of a particular geographic, political, or cultural region72. Question :What is the difference between a while statement and a do statement?
Answer :
A while statement checks at the beginning of a loop to see whether the next loop iteration should occur. A do statement checks at the end of a loop to see whether the next iteration of a loop should occur. The do statement will always execute the body of a loop at least once73. Question :What is the difference between static and non-static variables?
Answer :
A static variable is associated with the class as a whole rather than with specific instances of a class. Non-static variables take on unique values with each object instance74. Question :How are this() and super() used with constructors?
Answer :
This() is used to invoke a constructor of the same class. super() is used to invoke a superclass constructor75. Question :What are synchronized methods and synchronized statements?
Answer :
Synchronized methods are methods that are used to control access to an object. A thread only executes a synchronized method after it has acquired the lock for the method's object or class. Synchronized statements are similar to synchronized methods. A synchronized statement can only be executed after a thread has acquired the lock for the object or class referenced in the synchronized statement76. Question :What is daemon thread and which method is used to create the daemon thread?
Answer :
Daemon thread is a low priority thread which runs intermittently in the back ground doing the garbage collection operation for the java runtime system. setDaemon method is used to create a daemon thread77. Question :Can applets communicate with each other?
Answer :
At this point in time applets may communicate with other applets running in the same virtual machine. If the applets are of the same class, they can communicate via shared static variables. If the applets are of different classes, then each will need a reference to the same class with static variables. In any case the basic idea is to pass the information back and forth through a static variableAn applet can also get references to all other applets on the same page using the getApplets() method of java.applet.AppletContext. Once you get the reference to an applet, you can communicate with it by using its public members
It is conceivable to have applets in different virtual machines that talk to a server somewhere on the Internet and store any data that needs to be serialized there. Then, when another applet needs this data, it could connect to this same server. Implementing this is non-trivial
78. Question :What are the steps in the JDBC connection?
Answer :
While making a JDBC connection we go through the following steps :Step 1 : Register the database driver by using : Class.forName(\" driver classs for that specific database\" ); Step 2 : Now create a database connection using : Connection con = DriverManager.getConnection(url,username,password); Step 3: Now Create a query using : Statement stmt = Connection.Statement(\"select * from TABLE NAME\"); Step 4 : Exceute the query : stmt.exceuteUpdate();
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