Java Questions

- The Set interface provides methods for accessing the elements of a finite mathematical set

- Sets do not allow duplicate elements

- Contains no methods other than those inherited from Collection

- It adds the restriction that duplicate elements are prohibited

- Two Set objects are equal if they contain the same elements

Yes, we can. In order to compile a java program, we don't require any main method. But to execute a java program we must have a main in it (unless it is an applet or servlet). Because main is the starting point of a java program.

An abstract class is an incomplete class. An abstract class is defined with the keyword abstract . We cannot create an object of the abstract class because it is not complete. It sets a behavioral protocol for all its child classes.

Pass By Reference means the passing the address itself rather than passing the value. Passby Value means passing a copy of the value to be passed.

Use Interfaces when…

- You see that something in your design will change frequently.

- If various implementations only share method signatures then it is better to use Interfaces.

- You need some classes to use some methods which you don't want to be included in the class, then you go for the interface, which makes it easy to just implement and make use of the methods defined in the interface.

Use Abstract Class when…

- If various implementations are of the same kind and use common behavior or status then abstract class is better to use.

- When you want to provide a generalized form of abstraction and leave the implementation task with the inheriting subclass.

- Abstract classes are an excellent way to create planned inheritance hierarchies. They're also a good choice for nonleaf classes in class hierarchies.

If we print any object by using println() or print() methods.

The println() or print() methods internally calls tostring() method and prints the return value of toString() method.

Path and Classpath are operating system level environment variales. Path is used define where the system can find the executables(.exe) files and classpath is used to specify the location .class files.

A thread is a lightweight subprocess, a smallest unit of processing. It is a separate path of execution. It shares the memory area of process.

As shown in the above figure, thread is executed inside the process. There is context-switching between the threads. There can be multiple processes inside the OS and one process can have multiple threads.