What's the difference between an interface and an abstract class?

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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 implement multiple interfaces in your class.

2012-05-21, 2203👍, 0💬

An application needs to load a library before it starts to run, how to code??
An application needs to load a library before it starts to run, how to code?? One option is to use a static block to load a library before anything is called. For example, class Test { static { System.loadLibrary("path-to-li brary-file");} .... } When you call new Test(), the static block will be ca... 2012-05-18, 2381👍, 0💬

Jack developed a program by using a Map container to hold key/value pairs. He wanted to make a change to the map. He decided to
Jack developed a program by using a Map container to hold key/value pairs. He wanted to make a change to the map. He decided to make a clone of the map in order to save the original data on side. What do you think of it? ? If Jack made a clone of the map, any changes to the clone or the original map... 2012-05-16, 2363👍, 0💬

What is NullPointerException and how to handle it?
What is NullPointerException and how to handle it? When an object is not initialized, the default value is null. When the following things happen, the NullPointerException is thrown: --Calling the instance method of a null object. --Accessing or modifying the field of a null object. --Taking the len... 2012-05-17, 2352👍, 0💬

How to define an Abstract class?
How to define an Abstract class? A class containing abstract method is called Abstract class. An Abstract class can't be instantiated. Example of Abstract class: abstract class testAbstractClass { protected String myString; public String getMyString() { return myString; } public abstract string anyA... 2012-05-24, 2338👍, 0💬

Is Iterator a Class or Interface? What is its use?
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. 2012-05-23, 2312👍, 0💬

Name the containers which uses Border Layout as their default layout?
Name the containers which uses Border Layout as their default layout? Containers which uses Border Layout as their default are: window, Frame and Dialog classes. 2012-05-21, 2247👍, 0💬

What do you understand by Synchronization?
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 modif... 2012-05-22, 2237👍, 0💬

How could Java classes direct program messages to the system console, but error messages, say to a file?
How could Java classes direct program messages to the system console, but error messages, say to a file? The class System has a variable out that represents the standard output, and the variable err that represents the standard error device. By default, they both point at the system console. This ho... 2012-05-18, 2231👍, 0💬

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