Java Basics

1. By
SHRIDHAR B

2.  Java supports single-line and multi-line comments that is
very similar to c and c++
public class MyFirstJavaProgram{
/* this is my first java program
* this will print Hello World as output
* this is an example of multi-line comments
*/
public static void main(String args[])
{
//This is an Example of a single line comment
/* This is also an example of a single line comment */
}

3.  Class is a blue print from which individual objects are created.
public class Dog{
String breed;
int age;
String color;
void barking(){
}
void hungry(){
}
}

4.  Object is nothing but an instance of a class
 Objects have both state and behaviors
 Ex:
If we consider dog then its state is – name ,
breed and the behavior is barking, wagging ,running

5.  public class Puppy {
Public Puppy(String name) {
// This constructor has one parameter, name.
System.out.println("Passed Name is :"+ name );
}
public static void main(String[]args) {
// Following statement would create an object myPuppy
Puppy myPuppy =new Puppy("tommy");
}
}

6.  A class contain any of the following variable types
 Local Variables
Instance Variables
Class Variables

7. public class Test{
public void pupAge(){
int age =0;
age = age +7;
System.out.println("Puppy age is : "+age);
}
public static void main(String args[]){
Test test =new Test();
test.pupAge();
}
}

8. public class Test{
int age;
public void pupAge(){
System.out.println("Puppy age is :"+age);
}
public static void main(String args[]){
Test test =new Test();
test.pupAge();
}
}

9.  import java.io.*;
public class Employee{
public static final String DEPARTMENT="Development ";
public static void main(String args[]){
salary =1000;
System.out.println(DEPARTMENT+"averagesalary:"+sa
lary); }
}

10. public class Puppy {
public puppy(){
}
public puppy(String name) {
// This constructor has one parameter, name.
}
}

11.  Visible to the package, the default. No modifiers are
needed.
 Visible to the class only (private).
 Visible to the world (public).
 Visible to the package and all subclasses (protected).

12. package cert;
public class Sludge {
public void testIt() {
System.out.println("sludge");
}
}
package book;
import cert.*; // Import all classes in the cert package
class Goo {
public static void main(String[] args) {
Sludge o = new Sludge();
o.testIt();
}
}

13. public classLogger{
private String format;
public String getFormat()
{
return this.format;
}
public void setFormat(String format){
this.format = format;
}
}

14. package cert;
class Beverage {
}
package exam.stuff;
import cert.Beverage;
class Tea extends Beverage {
}
 Can't access class cert.Beverage. Class or interface must
be public, in same package, or an accessible member
class.

15. class AudioPlayer{
protected boolean openSpeaker(Speaker sp){
//implementation details
}
}
class StreamingAudioPlayer{
boolean openSpeaker(Speaker sp){
// implementation details
}
}

16.  Final
 Abstract
 Static
 Synchronized

17. package cert;
public final class Beverage {
public void importantMethod() {
}
}
package exam.stuff;
import cert.Beverage;
class Tea extends Beverage {
}
Can't subclass final classes: class
cert.Beverage class Tea extends Beverage{
1 error

18. Class Bank{
int accountBalance ;
public Bank(){
accountbalance = 10000;
}
Synchronized void BalanceInquiry(){
System.out.println(“account balance is
:”+accountbalance);
}
}

19. abstract class Hotel
{
public void Idli(){
System.out.println(“Prepare Idli”);
}
abstract public void Dosa();
}

20.  A literal is source code representation of a fixed
value
 Literals can be assigned to any primitive type
variable
 Ex:
byte a = 68;
int decimal = 100;
String name = “shridhar”

21.  Reference Data Types:
 Reference variables are created using defined
constructors of the classes. They are used to access
objects. These variables are declared to be of a specific
type that cannot be changed. For example, Employee,
Puppy, etc.
 Class objects and various types of array variables come
under reference data type.
 Default value of any reference variable is null.
 A reference variable can be used to refer to any object of
the declared type or any compatible type.
 Example: Animal animal = new Animal("giraffe");

22.  Instance variables and methods are accessed via
created objects.
/* First create an object */
ObjectReference = new Constructor();
/* Now call a variable as follows */
ObjectReference.variableName;
/* Now you can call a class method as follows */
ObjectReference.MethodName();

23. public class Puppy{
int puppyAge;
public Puppy(String name){
System.out.println("Passed Name is :"+name );
}
public void setAge(int age ){
puppyAge = age;
}
publicint getAge(){
System.out.println("Puppy's age is :"+ puppyAge );
return puppyAge;
}

24. public static void main(String[]args){
Puppy myPuppy =newPuppy("tommy");
myPuppy.setAge(2);
myPuppy.getAge();
/* You can access instance variable as follows as
well */
System.out.println("Variable Value :"+
myPuppy.puppyAge );
}
}