Java Eclipse

Question 1

What’s the first thing u do after creating a java project in eclipse

Answer 1

You create a package in src

Classes are created inside that package.

Question 2

How to get used input in java

Answer 2

Scanner scan = new Scanner(System.in);
X = scan.nextInt();

Question 3

How to create a sub class in java

Answer 3

public class child extends parent {…}

Question 4

How does JUnit work?

Answer 4

JUnit create a class separate from the class under test (business class). Inside this test class, we instantiate a business class object and specific methods in business class instance are called with known arguments and returned value is compared with known correct value using assrtEquals.

Each test method is annotated with
@Test

Question 5

In Eclipse, how do u create JUnit test case?

Answer 5

Right click on the class to be tested -> JUnit Test Case

Question 6

What are some assertion methods used in JUnit?

Answer 6

• assertEquals()
• assertNotEquals()
• assertTrue()
• assertNull()
  etc.

Question 7

What are some annotations used in JUnit?

Answer 7

@BeforeClass: This method is executed before any test is run. Used for setting up. Business class object may be instantiated here and used in other test cases.

@Before: This method is executed before each test case is run.

@Test: This annotation is prefixed before each test method.

@After: This method is executed after each test case is run.

@AfterClass: This method is executed after ALL test cases are run. Typically used to teardown the set up and free all resources.

Question 8

When is a jar file runnable?

Answer 8

The jar file should contain a class with a main() method.

Question 9

How to work with jar file?

Answer 9

Create jar file with a bunch of compiled java class files, with following cmd,
jar cvf  newFileName.jar  first.class second.class …

Check contents of jar file
jar tvf filename.jar

To run a jar file, we have to know the class we want to run,  say  xyz.class
Find full path to the class inside jar file

jar tvf filename.jar
Locat the line containing xyz.class, say
aa/bb/cc/xyz.class

run with following cmd,

java -cp /path/to/jar/file.jar aa/bb/cc/xyz

or

java -cp /path/to/jar/file.jar aa.bb.cc.xyz

Question 10

What is a package in java?

Answer 10

All classes should specifically be placed in named packages.

When you define a class, make first line in the file as

package myOwnPackage;

Then define your class, this will put the class in “myOwnPackage” pkg.

In other files, where that class is needed, put

import myOwnPackage;

import java.util.Date; // wil import Date class

import java.util.*; // Will import all classes in java.util

==> Date x = new Date();

If u don’t want to import entire package, use following,
java.util.Date x = new java.util.Date(); // No need for import

Question 11

What is java classpath?

Answer 11

When u run a jar file, u have to explicitly specify classpath using -cp, eg.

java -cp /path/to/jar/file.jar aa.bb.cc.xyz

Question 12

What is the structure of main() function in java?

Answer 12

public static void main(String[] args){
System.out.println(“Test - 1”);
}

Question 13

What is single import declaration?

Answer 13

When you import only one class from a package.

U explicitly specify packageName and className, like,

import pkgName.className;

Question 14

How do u import all classes from a package?

Answer 14

import pkgName.;
import java.util.;

This will import all classes from that pkg, BUT NOT FROM sub-packages.

Question 15

When compiling a class file which specifies a package, how do u create a directory structure at the time of compilation?

Answer 15

With -d option,

javac -d . myClass.java

Question 16

What is a servelet?

Answer 16

It is a part of web server which dynamically creates web pages and sends to browser. This is as opposed to sending/serving static HTML files.