JAVA Interview Questions&Answers Part 2

What are synchronized methods and synchronized statements?

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 statement.

What are three ways in which a thread can enter the waiting state?

A thread can enter the waiting state by invoking its sleep() method, by blocking on I/O, by unsuccessfully attempting to acquire an object's lock, or by invoking an object's wait() method. It can also enter the waiting state by invoking its (deprecated) suspend() method.

Can a lock be acquired on a class?

Yes, a lock can be acquired on a class. This lock is acquired on the class's Class object.

What's new with the stop(), suspend() and resume() methods in JDK 1.2?

The stop(), suspend() and resume() methods have been deprecated in JDK 1.2.

What is the preferred size of a component?
The preferred size of a component is the minimum component size that will allow the component to display normally.

What method is used to specify a container's layout?
The setLayout() method is used to specify a container's layout.

Which containers use a FlowLayout as their default layout?
The Panel and Applet classes use the FlowLayout as their default layout.

What is thread?
A thread is an independent path of execution in a system.

What is multithreading?
Multithreading means various threads that run in a system.

How does multithreading take place on a computer with a single CPU?
The operating system's task scheduler allocates execution time to multiple tasks. By quickly switching between executing tasks, it creates the impression that tasks execute sequentially.

How to create multithread in a program?

You have two ways to do so. First, making your class "extends" Thread class. Second, making your class "implements" Runnable interface. Put jobs in a run() method and call start() method to start the thread.

Can Java object be locked down for exclusive use by a given thread?
Yes. You can lock an object by putting it in a "synchronized" block. The locked object is inaccessible to any thread other than the one that explicitly claimed it

Can each Java object keep track of all the threads that want to exclusively access to it?
Yes

What state does a thread enter when it terminates its processing?
When a thread terminates its processing, it enters the dead state.

What invokes a thread's run() method?
After a thread is started, via its start() method of the Thread class, the JVM invokes the thread's run() method when the thread is initially executed.

What is the purpose of the wait(), notify(), and notifyAll() methods?
The wait(),notify(), and notifyAll() methods are used to provide an efficient way for threads to communicate each other.

What are the high-level thread states?
The high-level thread states are ready, running, waiting, and dead.

What is the Collections API?
The Collections API is a set of classes and interfaces that support operations on collections of objects.

What is the List interface?

The List interface provides support for ordered collections of objects.

How does Java handle integer overflows and underflows?
It uses those low order bytes of the result that can fit into the size of the type allowed by the operation.

What is the Vector class?
The Vector class provides the capability to implement a growable array of objects What modifiers may be used with an inner class that is a member of an outer class? A (non-local) inner class may be declared as public, protected, private, static, final, or abstract.

If a method is declared as protected, where may the method be accessed?
A protected method may only be accessed by classes or interfaces of the same package or by subclasses of the class in which it is declared.

What is an Iterator interface?
The Iterator interface is used to step through the elements of a Collection.

How many bits are used to represent Unicode, ASCII, UTF-16, and UTF-8 characters?
Unicode requires 16 bits and ASCII require 7 bits. Although the ASCII character set uses only 7 bits, it is usually represented as 8 bits. UTF-8 represents characters using 8, 16, and 18 bit patterns. UTF-16 uses 16-bit and larger bit patterns.

What is the difference between yielding and sleeping?
When a task invokes its yield() method, it returns to the ready state. When a task invokes its sleep() method, it returns to the waiting state.

Is sizeof a keyword?
The sizeof operator is not a keyword.

What are wrapped classes?
Wrapped classes are classes that allow primitive types to be accessed as objects.

Does garbage collection guarantee that a program will not run out of memory?
No, it doesn't. 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 collection

What is the difference between preemptive scheduling and time slicing?
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 factors.

Name Component subclasses that support painting.
The Canvas, Frame, Panel, and Applet classes support painting.

What is a native method?
A native method is a method that is implemented in a language other than Java.

How can you write a loop indefinitely?
for(;;)--for loop; while(true)--always true, etc.

Can an anonymous class be declared as implementing an interface and extending a class?
An anonymous class may implement an interface or extend a superclass, but may not be declared to do both.

What is the purpose of finalization?
The purpose of finalization is to give an unreachable object the opportunity to perform any cleanup processing before the object is garbage collected.

Which class is the superclass for every class.
Object.

What is the difference between the Boolean & operator and the && operator?
If an expression involving the Boolean & operator is evaluated, both operands are evaluated. Then the & operator is applied to the operand. When an expression involving the && operator is evaluated, the first operand is evaluated. If the first operand returns a value of true then the second operand is evaluated. The && operator is then applied to the first and second operands. If the first operand evaluates to false, the evaluation of the second operand is skipped.
Operator & has no chance to skip both sides evaluation and && operator does. If asked why, give details as above.

What is the GregorianCalendar class?
The GregorianCalendar provides support for traditional Western calendars.

What is the SimpleTimeZone class?
The SimpleTimeZone class provides support for a Gregorian calendar.

Which Container method is used to cause a container to be laid out and redisplayed?
validate()

What is the Properties class?
The properties class is a subclass of Hashtable that can be read from or written to a stream. It also provides the capability to specify a set of default values to be used.

What is the purpose of the Runtime class?
The purpose of the Runtime class is to provide access to the Java runtime system.

What is the purpose of the System class?
The purpose of the System class is to provide access to system resources.