Static variable context Errors ?

[Shyam Singh]

I m getting errors like this -->

1. Non-static variable cannot be referenced from a static context.

2. Static viariable cannot be referenced from non-static context.


Can any body clear my Concept about that.

[Norm]

Could you write a 10 line program that shows these errors and we'll explain.

[karthigr]

Hi

can any one help me how to load CSv file to table using java .

[Shyam Singh]

Could you write a 10 line program that shows these errors and we'll explain.

Norm i will ask about the 1st problem later .. pls give a look to this one -->


class exshyone {
int a;
exshyone() {
a=10;
System.out.println(a);
}
}

class shyone extends exshyone {

a=20;
System.out.println(a);
public static void main(String []ar) {
shyone one =new shyone();
}
}



Errors-->

D:\jdk1.5.0_06\bin\shyone.java:11: <identifier> expected
a=20;
^
D:\jdk1.5.0_06\bin\shyone.java:12: <identifier> expected
System.out.println(a);
^
2 errors



Questions -->

1. Can't I access variable 'a' of parent in child like the above prog.

2. why we require the construct to declare & initialize the variable in parent.

[Norm]

Program statements like a=20; must be inside a method or constructor.

why we require

The compiler isn't real smart and easily gets confused if you don't follow the rules.

[Shyam Singh]

but if i will put int 'a' in a constructor or function it will become local for that only. that means i cannot access that class level variable in the child class.

[Norm]

No, it means that you have hidden the 'a' in the Constructor. The parent's 'a' is still visible to other methods. Modify your above program to see.

[Shyam Singh]

Norm, i m able to access the variable declared in parent class in child one. here is the code-->


class Parent
{
int d=100;
void f1()
{
System.out.println("IN PARENT f1");

}

}

class Child1 extends Parent
{
void f2()
{
System.out.println("value of D"+d); // Here i m accessing the variable D of Class levl. var. of Parent
System.out.println("in Child1 f2");
// Child1 ob1=new Child2();
// ob1.f1();

}
}

/*
void f1() {
System.out.println("in Child1 f1");
}
}

*/


public class Child2 extends Child1
{

/*
void f2() {

System.out.println("In Child2 f2");
Child2 ob1=new Child2();
ob1.f1();
}
void f1() {
System.out.println("In Child2 f1");
}

*/

public static void main(String[] args)
{
Parent p=new Parent();
p.f1();

Child1 ob=new Child1();
ob.f2();

/* Child1 ch1=new Child1();
ch1.f2(); */
}
}



then why i m not able to do that in the previous code... reasons

[Norm]

i m not able to do that in the previous code

Can you be more specific?
what does do that mean? What variables in what methods/classes?

[Shyam Singh]

No, it means that you have hidden the 'a' in the Constructor. The parent's 'a' is still visible to other methods. Modify your above program to see.

Could u pls modify the code 1 for me ..i tried ..didn't work.

[Shyam Singh]

Norm, i m able to access the variable declared in parent class in child one. here is the code-->


class Parent
{
int d=100;
void f1()
{
System.out.println("IN PARENT f1");

}

}

class Child1 extends Parent
{
void f2()
{
System.out.println("value of D"+d); // Here i m accessing the variable D of Class levl. var. of Parent
System.out.println("in Child1 f2");
// Child1 ob1=new Child2();
// ob1.f1();

}
}

/*
void f1() {
System.out.println("in Child1 f1");
}
}

*/


public class Child2 extends Child1
{

/*
void f2() {

System.out.println("In Child2 f2");
Child2 ob1=new Child2();
ob1.f1();
}
void f1() {
System.out.println("In Child2 f1");
}

*/

public static void main(String[] args)
{
Parent p=new Parent();
p.f1();

Child1 ob=new Child1();
ob.f2();

/* Child1 ch1=new Child1();
ch1.f2(); */
}
}



then why i m not able to do that in the previous code... reasons

[Shyam Singh]

Can you be more specific?
what does do that mean? What variables in what methods/classes?

I hav tried the code 1 -->


class exshyone {
int a=100;
exshyone() {
a=10;
System.out.println(a);
}
}


class shyone extends exshyone {

void show() {

a=290;
System.out.println(a);
}

public static void main(String []ar) {

shyone one =new shyone();
one.show();

}
}

i m able to access var. ' a ' When i put

a=290;
System.out.println(a);

in any Function or in Cunstructor .

cant we execute the code like this -->


class exshyone {
int a=100;
exshyone() {
a=10;
System.out.println(a);
}
}


class shyone extends exshyone {

//void show() {

a=290;
System.out.println(a);

// }

public static void main(String []ar) {

shyone one =new shyone();
one.show();

}
}


if not wat is the reason java dont permit this code.

[Norm]

You don't say what the problem is?

java dont permit this code.

If you get errors, please copy them here.

[Shyam Singh]

Norm, i m able to access the variable declared in parent class in child one. here is the code-->


class Parent
{
int d=100;
void f1()
{
System.out.println("IN PARENT f1");

}

}

class Child1 extends Parent
{
void f2()
{
System.out.println("value of D"+d); // Here i m accessing the variable D of Class levl. var. of Parent
System.out.println("in Child1 f2");
// Child1 ob1=new Child2();
// ob1.f1();

}
}

/*
void f1() {
System.out.println("in Child1 f1");
}
}

*/


public class Child2 extends Child1
{

/*
void f2() {

System.out.println("In Child2 f2");
Child2 ob1=new Child2();
ob1.f1();
}
void f1() {
System.out.println("In Child2 f1");
}

*/

public static void main(String[] args)
{
Parent p=new Parent();
p.f1();

Child1 ob=new Child1();
ob.f2();

/* Child1 ch1=new Child1();
ch1.f2(); */
}
}



then why i m not able to do that in the previous code... reasons

[Shyam Singh]

Norm, i m able to access the variable declared in parent class in child one. here is the code-->


class Parent
{
int d=100;
void f1()
{
System.out.println("IN PARENT f1");

}

}

class Child1 extends Parent
{
void f2()
{
System.out.println("value of D"+d); // Here i m accessing the variable D of Class levl. var. of Parent
System.out.println("in Child1 f2");
// Child1 ob1=new Child2();
// ob1.f1();

}
}

/*
void f1() {
System.out.println("in Child1 f1");
}
}

*/


public class Child2 extends Child1
{

/*
void f2() {

System.out.println("In Child2 f2");
Child2 ob1=new Child2();
ob1.f1();
}
void f1() {
System.out.println("In Child2 f1");
}

*/

public static void main(String[] args)
{
Parent p=new Parent();
p.f1();

Child1 ob=new Child1();
ob.f2();

/* Child1 ch1=new Child1();
ch1.f2(); */
}
}



then why i m not able to do that in the previous code... reasons

[Shyam Singh]

if i write like this (without function or Cunstructor ) -->


class exshyone {
int a=100;
exshyone() {
a=10;
System.out.println(a);
}
}


class shyone extends exshyone {

//void show() {

a=290; // Here (like this)
System.out.println(a);

// }

public static void main(String []ar) {

shyone one =new shyone();
one.show();

}
}


Errors-->


D:\jdk1.5.0_06\bin\shyone.java:15: <identifier> expected
a=290;
^
D:\jdk1.5.0_06\bin\shyone.java:16: <identifier> expected
System.out.println(a);
^
2 errors

[Shyam Singh]

Norm, i m able to access the variable declared in parent class in child one. here is the code-->


class Parent
{
int d=100;
void f1()
{
System.out.println("IN PARENT f1");

}

}

class Child1 extends Parent
{
void f2()
{
System.out.println("value of D"+d); // Here i m accessing the variable D of Class levl. var. of Parent
System.out.println("in Child1 f2");
// Child1 ob1=new Child2();
// ob1.f1();

}
}

/*
void f1() {
System.out.println("in Child1 f1");
}
}

*/


public class Child2 extends Child1
{

/*
void f2() {

System.out.println("In Child2 f2");
Child2 ob1=new Child2();
ob1.f1();
}
void f1() {
System.out.println("In Child2 f1");
}

*/

public static void main(String[] args)
{
Parent p=new Parent();
p.f1();

Child1 ob=new Child1();
ob.f2();

/* Child1 ch1=new Child1();
ch1.f2(); */
}
}



then why i m not able to do that in the previous code... reasons