basic concvept of java

1. JAVA CLASS AND
OBJECTS
By: Dr. Sangeeta Sen

2. Declare and Allocate
Example:
int myArray [ ] [ ];
myArray = new int [3] [4];
OR
int myArray [ ] [ ] = new int [3] [4];
Initializing a 2D array :
An example
int myArray [2] [3] = {1, 2, 3, 4, 5, 6};
OR
int myArray [ ] [ ] = { {1, 2, 3}, {4, 5, 6} };
Creating and initializing 2D array

3. public class Boy{
String name;
String address;
int age;
public static void main(String[] args) {
Boy obj = new Boy();
obj.name = “Rohan";
obj.address = “Durgapur";
obj.age = 23;
System.out.println("Name of the boy is:
"+obj.name);
System.out.println("Address of the boy is:
"+obj.address);
System.out.println("Age of the boy is: "+obj.age);
}}
Class and its object creation in Java
Syntax for creating an object in Java is as shown below:
ClassName object-reference = new ClassName();

4. Class and its object creation in Java
Objects are created dynamically in the heap
area inside RAM (Random Access Memory).

5. Class and its object creation in Java
public class Boy{
String name;
String address;
int age;
void printData(String x, String y, int a){
name = x;
address = y;
age = a ;
System.out.println("Name of the boy is: "+name);
System.out.println("Address of the boy is: "+address);
System.out.println("Age of the boy is: "+age);}
public static void main(String[] args) {
Boy obj = new Boy();
obj.printData("Riya", "Durgapur", 23); }}

6. public class StringTest {
public static void main(String[] args) {
String[] authors = {"Herbert Schildt","Ivor Horton","Josuah Boch","Debasis Roy",
"Gary Cornell"};
System.out.println("The best author is " + authors[0]);
System.out.print("n" + authors[4]);
System.out.println();
System.out.println(authors[3]);
System.out.println(authors[5]);
}
}
Guess the output

7. Write programs
Following is a small program in C. Write an
equivalent program using Java language.
#include……
int main() {
int x = 10, y = 3;
int a, b;
a = x + y;
b = x - y;
printf(“x + y = %dn”, a);
printf(“x - y = %dn”, b);
getch();
return 0;
}
Write an equivalent program of the following program using Java
language.
#include …..
void main() {
int i = 0;
printf(“Enter a value of i : “);
scanf(“%d”, &i);
printf(“n n i = %d, i++ = %d, ++i = %dn”, i, i++, i++);
return; }
Scanner scan = new Scanner(System.in);
System.out.print("Enter a value of i : ");
i = scan.nextInt();

8. Class and its object creation in Java
1. Program to Print a Welcome Message (class name: WelcomeMessage, object
name: wm, method name: printMessage())
2. Program to Find Area of a Rectangle (class name: Rectangle, object name: c,
method name: calArea())
3. Program to Multiply Two Numbers (class name: Product, object name: p, method
name: multiplyNo())
4. Program to Display Bank Account Details of two account holder (class name:
Bank, object name: b1, b2, method name: printDetails(name, account details))

9. class Circle {
double r;
double circumference() {
return 2 * 3.14159 * r; }
double area() {
return (22 / 7) * r * r; }}
class CircleTest {
public static void main(String args[]) {
Circle c1 = new Circle();
c1.r = 12.36;
System.out.println("Area = " + c1.area() + "t" + "Circumference= " + c1.circumference()); }}
Class and its object creation in Java