Abstract Demo

import java.util.Scanner;
/*1*/abstract class vehicle5
{
private int wheel;
vehicle5()
{
System.out.println("Some vehicles instanciated");
wheel=4;
}
void start()
{
System.out.println("Every vehicle starts like this");
}
abstract void move();
}
class car6 extends vehicle5
{
void move()
{
System.out.println("Exellent transportation");
}
}
class zeep extends vehicle5
{
void move()
{
System.out.println("Good transportation");
}
}
class AbstractExample {

public static void main(String[] args) {
vehicle5 v;
Scanner s = new Scanner(System.in);
System.out.println("What vehicle you want car/zeep");
String choice=s.next();
if(choice.equals("car"))
v=new car6();
/*if(choice.equals("zeep"))
v=new zeep();*/ //error
else
v=new zeep();
v.start();
v.move();
}
}

nested class

class A
{
static class B
{

}
class C
{

}
}
class nestedclass
{
public static void main(String args[])
{
  A a = new A();//outer class instance created.
  A.B b = new A.B();//nested class instance.
  A.C c = new C();//inner class instance created.
}
}

use different classes data with one class with object in java

save as class1.java

/*accessing 1 class member into another class member*/
class class1
{
int a=100,b=100;
void fun1()
{
System.out.println("i am class1 and in fun1()");
}
void fun2()
{
System.out.println("i am class1 and in fun2()");
}


public static void main(String args[])
{
/*class1 class1 = new class1();
System.out.println("a :"+class1.a);
System.out.println("b :"+class1.b);

class1.fun1();
class1.fun2();*/
}
}

================================================
save as class2.java

/*accessing 1 class member into another class member*/
class class2
{
int a=200,b=200;
void fun1()
{
System.out.println("i am class2 and in fun1()");
}
void fun2()
{
System.out.println("i am class2 and in fun2()");
}


public static void main(String args[])
{
/*class2 class2 = new class2();
System.out.println("a :"+class2.a);
System.out.println("b :"+class2.b);

class2.fun1();
class2.fun2();*/
}
}

============================================
save as class3.java

/*accessing 1 class member into another class member*/
class class3
{
int a=300,b=300;
void fun1()
{
System.out.println("i am in class3 and fun1()");
}
void fun2()
{
System.out.println("i am in class3 and fun2()");
}


public static void main(String args[])
{

class1 class1 = new class1();
class2 class2 = new class2();
class3 class3 = new class3();


System.out.println("\na in class 1 :"+class1.a);
System.out.println("b in class 1 :"+class1.b);
class1.fun1();
class1.fun2();

System.out.println("\na in class 2 :"+class2.a);
System.out.println("b in class 2 :"+class2.b);
  class2.fun1();
  class2.fun2();

System.out.println("\na in class 3 :"+class3.a);
System.out.println("b in class 3 :"+class3.b);
class3.fun1();
class3.fun2();
}
}

====================================================
run :
        class3.java
 ==================================================
output :

i am in class1 and fun1()
i am in class1 and fun2()
a in class 1 :300
b in class 1 :300

i am in class3 and fun1()
i am in class3 and fun2()
a in class 2 :300
b in class 2 :300


i am in class3 and fun1()
i am in class3 and fun2()
a in class 3 :300
b in class 3 :300

multiple classes and mains in java

save as "multiplemain.java"
========================================
class a
{
public static void main(String args[])
{
System.out.println("i am in class a");
}
}
class b
{
public static void main(String args[])
{
System.out.println("i am in class b");
}
}

class c
{
public static void main(String args[])
{
System.out.println("i am in class c");
}
}

=============================================
how to run :
by default "class a" will run
so , output is " i am in class a"

to run any class , open command prompt and run as fallows

start  > run > type "cmd" > open the directory in command prompt where java installed and your java program is stored within java programs

And type as fallows

javac  multiplemain.java (press enter)
java a (press enter)
or
java b (press enter)
or
java c  (press enter)

=============================================
ex ample :

   C:\Program Files\Java\jdk1.6.0_07\bin\javac  multiplemain.java  (press enter)

   C:\Program Files\Java\jdk1.6.0_07\bin\java a  (press enter)
    or
   C:\Program Files\Java\jdk1.6.0_07\bin\java b  (press enter)
    or
   C:\Program Files\Java\jdk1.6.0_07\bin\java c  (press enter)

=============================================

output :

i am in a
or
i am in b
or
i am in c

default values of reference in java

class defaultref
{
double p,q;
defaultdemo defdemmo;
public static void main(String args[])
{
defaultref ref= new defaultref();
System.out.println("p :"+ref.p);
System.out.println("q :"+ref.q);
System.out.println("s :"+ref.defdemmo);

System.out.println("byte :"+ref.defdemmo.b);
System.out.println("short :"+ref.defdemmo.s);
System.out.println("long :"+ref.defdemmo.l);
System.out.println("int :"+ref.defdemmo.i);
System.out.println("float :"+ref.defdemmo.f);
System.out.println("double :"+ref.defdemmo.d);
System.out.println("char :"+ref.defdemmo.ch);
System.out.println("boolean:"+ref.defdemmo.bl);
}
}
======================================================
output :

p :0
q :0
s :null

And for others null pointer exception will show

default values in java

class defaultdemo
{
byte b;
short s;
int i;
long l;
float f;
double d;
char ch;
boolean bl;
public static void main(String args[])
{
defaultdemo d=new defaultdemo();
System.out.println("byte :"+d.b);
System.out.println("short :"+d.s);
System.out.println("long :"+d.l);
System.out.println("int :"+d.i);
System.out.println("float :"+d.f);
System.out.println("double :"+d.d);
System.out.println("char :"+d.ch);
System.out.println("boolean:"+d.bl);
}
}
====================================================
output :
b :0
s :0
i :0
l :0
f :0.0
d :0.0
char : (single space value)
bl : false

accessing members of one class inside another in java

save below 3 classes in 1 file
name like  "name.java" without quotes
================================================
class sample
{
int a=100,b=200;
void funA()
{
System.out.println("i am in A function");
}
void funB()
{
System.out.println("i am in B function");
}
void funC()
{
System.out.println("i am in C function");
}
}


class demo1
{
public static void main(String args[])
{
sample s=new sample();
System.out.println("a :"+s.a);
System.out.println("b :"+s.b);
s.funA();
s.funB();
s.funC();
}
}


class demo2
{
sample s=new sample();
public static void main(String args[])
{
double p=12.5,q=13.5;
demo2 od=new demo2();
System.out.println("a :"+od.s.a);
System.out.println("b :"+od.s.b);
od.s.funA();
od.s.funB();
od.s.funC();
}
}

object in java sample program

class sample
{
int a=100,b=200;
void fun1()
{
System.out.println("i am in fun1()");
}
void fun2()
{
System.out.println("i am in fun2()");
}
public static void main(String args[])
{
int c=300;
sample s = new sample();
System.out.println("a :"+s.a);
System.out.println("b :"+s.b);

s.fun1();
s.fun2();

System.out.println("c :"+c);
}
}
==============================================
output :
a: 100
b: 200
i am in fun1()
i am in fun2()
c :300