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Vector and ArrayList Classes
What is the main difference between a Vector and an ArrayList? Java Vector class is internally synchronized and ArrayList is not. 2007-03-03, 7054👍, 0💬

Virtual Functions in Java
Can you have virtual functions in Java? Yes, all functions in Java are virtual by default. This is actually a pseudo trick question because the word "virtual" is not part of the naming convention in Java (as it is in C++, C-sharp and VB.NET), so this would be a foreign concept for someone who has on... 2007-03-03, 6971👍, 0💬

Waiting State in a Thread
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 IO, 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 invoki... 2007-03-03, 6602👍, 0💬

Native Method
What is a native method? A native method is a method that is implemented in a language other than Java. 2007-03-03, 6509👍, 0💬

What is Java
What is Java? Java is an object-oriented programming language developed initially by James Gosling and colleagues at Sun Microsystems. The language, initially called Oak (named after the oak trees outside Gosling's office), was intended to replace C++, although the feature set better resembles that ... 2007-03-03, 6370👍, 0💬

What is Collection API
What is Collection API? The Collection API is a set of classes and interfaces that support operation on collections of objects. These classes and interfaces are more flexible, more powerful, and more regular than the vectors, arrays, and hashtables. Example of classes: HashSet, HashMap, ArrayList, L... 2007-03-03, 6226👍, 0💬

sleep() and yield() Methods
What is the difference between yielding and sleeping? When a thread invokes its yield() method, it returns to the ready state. When a thread invokes its sleep() method, it returns to the waiting state. 2007-03-03, 6143👍, 0💬

Garbage Collection
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. 2007-03-03, 6102👍, 0💬

Defining an Interface
How to define an Interface? Java Interface defines methods but does not implement them. Interface can include constants. A class that implements an interface is required to implement all the methods defined in the interface. Here is an example of interface definition: public interface MyInterface { ... 2007-03-03, 6093👍, 0💬

Differences between Interfaces and Abstract Classes
What's the difference between an interface and an abstract class? An abstract class may contain code in method bodies, which is not allowed in an interface. With abstract classes, you have to inherit your class from it and Java does not allow multiple inheritance. On the other hand, you can implemen... 2007-03-03, 6031👍, 0💬

Synchronized Methods and Synchronized Statements
What are synchronized methods and synchronized statements? Synchronized methods are methods that are used to control access to a method or 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 s... 2007-03-03, 6020👍, 0💬

Component Subclasses in Swing Package
Name Component subclasses that support painting? The Canvas, Frame, Panel, and Applet classes support painting. 2007-03-03, 5953👍, 0💬

Wrapped Classes
What are wrapped classes? Wrapped classes are classes that allow primitive types to be accessed as objects. 2007-03-03, 5949👍, 0💬

Acquiring Locks on Classes
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. 2007-03-03, 5934👍, 0💬

Swing BorderLayout and Contrainer Classes
Name the containers which uses Border Layout as their default layout? Swing container classes which uses BorderLayout as their default are: Window, Frame and Dialog classes. 2007-03-03, 5912👍, 0💬

Transient Variables
What is a transient variable? A transient variable is a variable that may not be serialized. If you do not want some variables to be serialized, you can mark those variables transient or static. 2007-03-03, 5887👍, 0💬

Externalizable Interface: readExternal() and readExternal()
How many methods in the Externalizable interface? There are two methods in the Externalizable interface. You have to implement these two methods in order to make your class externalizable. These two methods are readExternal() and readExternal(). 2007-03-03, 5864👍, 0💬

Serializable Interface
How many methods in the Serializable interface? There is no method in the Serializable interface. The Serializable interface acts as a marker, telling the object serialization tools that your class is serializable. 2007-03-03, 5858👍, 0💬

Observer Interface and Observable Class
How are Observer and Observable used? 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 obj... 2007-03-03, 5825👍, 0💬

Iterator Interface
Is Iterator a Class or Interface? What is its use? Iterator is an interface which is used to step through the elements of a Collection. 2007-03-03, 5805👍, 0💬

Defining Abstract Classes
How to define an Abstract class? Defining an abstract class is done using the keyword "abstract". Here is an example of abstract class: abstract class MyAbstract { protected String myString; public String getMyString() { return myString; } public abstract string getMyStringInYourWay(); } 2007-03-03, 5787👍, 0💬

Preemptive Scheduling
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 the... 2007-03-03, 5776👍, 0💬

Serializalble and Externalizable Interfaces
What is the difference between Serializalble and Externalizable interface? When you use Serializable interface, your class is serialized automatically by default. But you can override writeObject() and readObject() two methods to control more complex object serailization process. When you use Extern... 2007-03-03, 5743👍, 0💬

Modifiers on Inner Classes
What modifiers may be used with an inner class that is a member of an outer class? A inner class may be declared as public, protected, private, static, final, or abstract. 2007-03-03, 5722👍, 0💬

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.NET C C++ CSS DBA General HTML Java JavaScript JSP JUnit MySQL Networking Oracle Perl Perl PHP PL/SQL RSS Software QA SQL Server Struts Unix Windows XHTML XML