Java program
1. local variable program
//local variable
class Ram
{
public void student_age()
{
int age=0; //local variable
age=age+5;
//defined in block can't use outside block
}
public static void main(String args[])
{
//using local variable outside scope
System.out.println("age : "+ age);
}
}
output :
Program generate error
2.class variable program
// class variable
class Ram
{
static int count; // class variable
public static void main(String args[])
{
Ram obj1=new Ram(); // obj1 is created for class Ram
Ram obj2=new Ram(); // obj2 is created for class Ram
obj1.count=15;
obj2.count=15;
obj1.count++; //change in count of object 1
System.out.println(obj1.count);
System.out.println(obj2.count);
}
}
output :
16
16
3. constructor program
// constructor
class person
{
private
String name;
person() // this is constructor
{
name="raj"; // initialize
}
void show()
{
System.out.println("name is : "+name);
}
}
class Ram
{
public static void main(String args[])
{
person obj=new person();// constructor ko call nhi krna automatic call when object is created
obj.show();
}
}
Output : name is raj
4. instance variable
//instance variable
class marks
{
int english,math;// instance variable inside class but outside function
}
class Ram
{
public static void main(String args[])
{
marks obj1=new marks();
obj1.english=20; //object ke through value initli
obj1.math=30; //object ke through value initli
marks obj2=new marks();
obj2.english=50; //object ke through value initli
obj2.math=80; //object ke through value initli
System.out.println("first object : "+obj1.english);
System.out.println("first object : "+obj1.math);
System.out.println("second object : "+obj2.english);
System.out.println("second object : "+obj2.math);
}
}
output :
first object : 20
first object : 30
second object : 50
second object : 80
5.java string
- string is a sequence of character but in java string is an object that represent //sequence of charcters.
- java.lang.string class का उपयोग string object बनाने के लिए करते है
//Java string
class Ram
{
public static void main(String args[])
{
String[] sub={"java","sql","c++","c"};
System.out.println(sub[0]);
System.out.println(sub.length);
//sub is object , // length एक function है object के साथ function लगा कर use किया है
}
}
output :
Java
4
6.java string
class Ram
{
public static void main(String args[])
{
String str="hellow, this is sample program";
char p[]=new char[20];
str.getChars(7,20,p,0); //obj.fx(paramtr)
//7- starting position
//20- ending position
//p - destination - जहा भेजना है
//0 - destination starting point
//getChars एक method है जो string मे से charcter copy कर लेता है
System.out.println(p);
}
}
output:
this is samp
7. java string
class Ram
{
public static void main(String args[])
{
String str="hellow, this is sample program";
System.out.println(str.toUpperCase());
System.out.println(str.toLowerCase());
System.out.println(str.indexOf("this"));
}
}
output:
HELLOW, THIS IS SAMPLE PROGRAM
hellow, this is sample program
suppose string s1="welcome" or string s2="welcome" , इस case मे केवल एक object create होगा
JVM एक string constant pool होता है उसके अंदर welcome को रख लेते है , पहली बार जब s1 बनाते है तो उसमे welcome है जब दोबारा s2 create किया जाता है तो नया object बनाने की जगह पहले वाले का refference return करते है .string जो object होते है वो special memory area मे store होते है जिसे string constant pool कहते है
StringBuffer भी string की तरह ही होता है लेकिन उसे modify किया जा सकता है इसे StringBuffer कहते है . जो string होता है वो immutable होता है can't be modified.जब की string buffer mutable होता है।
INHERITENCE
//extend keyword use in java for inheritence
//multiple inheritence is not supported java through class. when one class inherit multiple classes it is known as multiple inheritence.
//जब किसी class के एक से ज्यादा parent हो same level पर
//for ex : there is an three classes A,B,C ---- C class inherit A&B Class. if A&B have the same method now you can call it from child class object
// there will be ambiguity to call the method of A&B. <<--why java not support multiple inheritence?
8. Inheritence
// work in inheritence
class doctor
{
void ddetail()
{
System.out.println("this is doctor detail");
}
}
class surgun extends doctor
{
void sdetail()
{
System.out.println("this is surgun detail");
}
}
class Ram
{
public static void main(String args[])
{
surgun obj = new surgun();
obj.ddetail();
obj.sdetail();
}
}
output :
this is doctor detail
this is surgun detail
9. multi Inheritence
class doctor
{
void ddetail()
{
System.out.println("this is doctor detail");
}
}
class surgun extends doctor
{
void sdetail()
{
System.out.println("this is surgun detail");
}
}
class phy extends surgun
{
void pdetail()
{
System.out.println("this is phy detail");
}
}
class Ram
{
public static void main(String args[])
{
phy obj = new phy();
obj.ddetail();
obj.sdetail();
obj.pdetail();
}
}
output :
this is doctor detail
this is surgun detail
this is phy detail
OVERRIDDING METHOD
- जब same name का function base class और derived class दोनों मे available हो और function का signature //(function type, parameter)same हो तो ऐसे situation को function overriding कहते है
- class B मे show function है उसे overridden हुआ है , class A का show function hidden रहा है
//question - difference b/w overloading and overridding ?
10. overridding program
//method overriding
class A
{
void show()
{
System.out.println("this is doctor detail");
}
}
class B extends A
{
void show()
{
System.out.println("this is surgun detail");
}
}
class Ram
{
public static void main(String args[])
{
B obj = new B();
obj.show();
}
}
output :
this is surgun detail
VECTOR CLASS
- //vector class - vector class dynamic array की तरह होता है जो अपने size को shrink/grow कर सकता है .
- //इसकी default capicity 10 होती है इसका मतलब तब vector resize होगा जब 11 element vector मे शामिल होगा फिर इसकी capicity 20 हो जाएगी
11. vector class
// vector class
import java.util.*;
class Ram
{
public static void main(String args[])
{
Vector<String> v=new Vector<String>();
v.add("Tiger");
v.add("Lion");
System.out.println(v);
}
}
output:
[Tiger,Lion]
12. vector class - integer
import java.util.*;
class Ram
{
public static void main(String args[])
{
int n=5;
Vector<Integer> v=new Vector<Integer>(n);
for(int i=0;i<n;i++)
v.add(i);
System.out.println(v);
v.remove(3);
System.out.println(v);
}
}
output :
1 2 3 4 5
1 2 4 5
WRAPPER CLASS
- wrapper class - java मे जो wrapper class होती है वो primitive data type(int , float) को object के रूप मे काम लेने के लिए करते है इसके throgh premitive type को object मे बदला जा सकता है और vice versa भी ये java.util package मे available होती है।
- primitive type object नहीं होते है इसलिए वो किसी class से सम्बन्ध नहीं रखते।
//primitive type -> wrapper classes - example
// boolean -> Boolean,char -> Character , int -> Integer , float-> Float, double -> Double
13. Wrapper class
// program : primitive type convert into object type
import java.util.*;
class Ram
{
public static void main(String args[])
{
int num=100; // ये primitive type है
Integer p=Integer.valueOf(num); //num को object मे बदल रहा है
// num int है = से इसे भेजा जा रहा है , obj मे , obj की type class है
//char p = 5 -- ये लाइन गलत है लेकिन ये देखने के लिए की int 5 को char p मे भेजा जा रहा है |
System.out.println(p);
}
}
output :
100
14. wrapper class
// program : object convert into primitive type
import java.util.*;
class Ram
{
public static void main(String args[])
{
Integer obj= new Integer(100); // class है , class का variable है [object भी ] ,
int num=obj.intValue(); // object के साथ (.)dot लगा के function की call करी है //जो आया उसे num को दिया
System.out.println(num);
}
}
output :
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