Part 2

Question 1

What command (CLI) can we use to run a Java application?

Answer 1

java

eg: $ java Main

Question 2

What command (CLI) we can use to compile Java source code to bytecode and create a class file?

Answer 2

javac

eg: $ javac Main.java

Question 3

What command (CLI) we can use to disassemble one or more class files?

Answer 3

javap

Question 4

What command (CLI) we can use to create JMOD files and list the content of existing JMOD files?

Answer 4

jmod

Question 5

What command (CLI) we can use to generate HTML pages of API documentation from Java source files?

Answer 5

javadoc

Question 6

How we can check with command (CLI) the java version?

Answer 6

java -version

Question 7

What command we can use to manage a keystore(database) of cryptographic keys?

Answer 7

keytool

Question 8

How we can sign and verify Java Archive files (JAR)? (CLI)

Answer 8

jarsigner

Question 9

What command (CLI) we can use to read and write a plain text policy file based on user input through the utility GUI?

Answer 9

policytool

Question 10

What command (CLI) we can use to start a graphical console to monitor and manage Java applications?

Answer 10

jconsole

Question 11

What command we can use to list the instrumented JVMs on the target systems?

Answer 11

jps

Question 12

What command we can use to launch Java Mission Control (JMS) - profiling monitoring diagnostics tool suite?

Answer 12

jmc

Question 13

What compiler’s javac command line option defines directory paths in search of classes?

Answer 13

javac -classpath

Question 14

What interpreter’s command line option defines directory paths to use at runtime?

Answer 14

java -classpath

Question 15

What interpreter’s command line option we can use to set a system property value, what is its syntax?

Answer 15

java -D

java -Dproperty=value

Question 16

What command line option can be applied either to interpreter or compiler to print out the tool’s usage information?

Answer 16

java -h

Question 17

Which are the only applicable access modifiers for top level class?

Answer 17

public, , final, abstract, strictfp

Question 18

Which are the applicable access modifiers for inner classes?

Answer 18

public, , final, abstract, strictfp, private, protected, static

Question 19

What is it mean when a class is declared as public?

Answer 19

If a class is declared as public that we can access that class from anywhere, within the package or outside the package. 
public class Text {..}

Question 20

What is it mean when the class declaration doesn’t content any access modifier?

Answer 20

If class doesn't include any modifier in declaration, it has the default modifier that means that class is accessible only within the same package. 
class Text {..}

Question 21

What can be declared as final in java code?

Answer 21

Final is modifier applicable for classes, methods and fields.

Question 22

What is it mean when class is declared as final?

Answer 22

If class is declared as final then we can’t create the child class, the inheritance concept is not applicable for final classes. 
public final class Text {..}
Every method that is presented inside final class is always final by default whether we are declaring it or not. 
But every variable inside final class need not to be final. 
The final methods cannot be overriden in child class.

Question 23

What is it meant when method is declared as final?

Answer 23

The final methods cannot be overriden in child class.

Question 24

What kind of methods the final class can contain?

Answer 24

Every method that is presented inside final class is always final by default whether we are declaring it or not. 
But every variable inside final class need not to be final.

Question 25

What is it mean when the instance variable is declared as final?

Answer 25

If the instance variable is declared as the final compulsory we should perform initialization explicitly and JVM won't provide any default values. Rule: For the final instance variables we should perform initialization before constructor completion, otherwise we will get compile-time error.

Question 26

What is it mean when the variable is declared as final static?

Answer 26

``` If the value of a variable is not varied from object to object such type of variable is not recommended to declare as the instance variables. We have to declare those variables at class level by using static modifier. In case of instance variable for every object a separate copy will be created but in the case of static variable a single copy will be created at class level and shared by every object of that class. For the static variables it is not required to perform initialization explicitly, jvm will provide default values. ``` ``` If the static variable is declared as final the compulsory we should perform initialization explicitly, jvm won't provide any default value. Rule: For the final static variables we should perform initialization before class loading completion, otherwise we will get compile time error. Initialization inside static block is allowed: class Test { final static int=10; // this is ok } ``` ``` class Test { final static int i; static { i = 10; // inside static block is ok } } ```

Question 27

What can be declared with abstract modifier?

Answer 27

Abstract modifier can be used for classes and methods only (not for members.)

Question 28

What can be declared with abstract modifier?

Answer 28

Abstract modifier can be used for classes and methods only (not for members.)

Question 29

What is it mean when class is declared as abstract?

Answer 29

``` Abstract modifier can be used for classes and methods only (not for members.) abstract class - it means it is not complete or partially implemented class it is not possible to create an object of that abstract class, so abstract class cannot be instantiated. ```

Question 30

Has to abstract class contain abstract methods?

Answer 30

Abstract class can contain 0 abstract methods, if there are no abstract methods inside the class, that class can still be declared as abstract.

Question 31

Has to class be declared as abstract, if the class contains only one abstract method?

Answer 31

If class contents at least one abstract method, it needs to be declared as abstract.