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What is the use of Web2py's Field.Method?


What is the use of Web2py's Field.Method?

By : user2948303
Date : November 14 2020, 04:48 PM
To fix this issue I wanted to know what does the - Field.Method means/ What is the use of this function ? , It's basically a calculated db field. From the book:
code :


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A field defined by a method that uses that same field... circular definition in Java is hurting my head

A field defined by a method that uses that same field... circular definition in Java is hurting my head


By : DvanZ
Date : March 29 2020, 07:55 AM
wish helps you I came across this code on Vogella which demonstrates creating a LabelProvider for a JFACE tree. , You're confused because of the method overloading. The calls here:
code :
private static final Image FOLDER = getImage("folder.gif");
private static final Image FILE = getImage("file.gif");
public Image getImage(Object element) {
private static Image getImage(String file) {
// Bogus code!
private static Image FOLDER = getImage("folder.gif");
private static Image FILE = getImage("file.gif");

private static Image getImage(String name)
{
    return name.equals("FRED") ? FOLDER : FILE;
}
error CS0236: A field initializer cannot reference the non-static field, method, or property

error CS0236: A field initializer cannot reference the non-static field, method, or property


By : astro
Date : March 29 2020, 07:55 AM
should help you out I agree with @David You cant write such a code in class definition . You must write that part bool=.... inside either Constructor or a Method.
Calling method that modifies a field while another method that uses that field is executing

Calling method that modifies a field while another method that uses that field is executing


By : dmitriy platonov
Date : March 29 2020, 07:55 AM
Hope this helps Since you only have 1 thread of execution, and you do not have anything to change the while loop exit condition in the bar function, this code will loop forever. Your baz function will never be called.
A field initializer cannot reference the non-static field, method, or property 'FullmessageController.readsql'

A field initializer cannot reference the non-static field, method, or property 'FullmessageController.readsql'


By : shireesha
Date : March 29 2020, 07:55 AM
hope this fix your issue The right approach here depends on whether you actually want multiple fields. If you want two fields, one for the ReadSQL and one for the QueryHandler, you can do that like this, initializing the fields within the constructor:
code :
// Names adjusted for convention
class Whatever
{
    private ReadSql readSql;
    private QueryHandler queryHandler;

    public Whatever()
    {
        readSql = new ReadSql();
        queryHandler = new QueryHandler(readSql);
    }
}
// Names adjusted for convention
class Whatever
{
    private QueryHandler queryHandler = new QueryHandler(new ReadSql());
}
superclass with private static field and subclass calls a method that changes the field, Why doesn't the field change?

superclass with private static field and subclass calls a method that changes the field, Why doesn't the field change?


By : user1496616
Date : March 29 2020, 07:55 AM
Hope this helps The reason is well explained inPanz0r's answer but what you don't see is that you have two variable call bar, one in A one in B.
If you add a method to print the instance members in both class (and A will also print is super class):
code :
public class Main {

    public static void main(String[] args) {
        B base = new A();
        System.out.println(base);
    }
}

class B {

    private static boolean goo = true;

    protected static boolean foo() {
        goo = !goo;
        return goo;
    }

    public String bar = "Base:" + foo();

    @Override
    public String toString() {
        return bar; //print the variable B.bar
    }
}

class A extends B {
    public String bar = "Sub:" + foo();

    @Override
    public String toString() {
        //print the instance B and the variable A.bar
        return super.toString() + "\n" + bar;
    }
}
public String bar;

public B(){
    this("Base: ");
}

protected B(String source){ //protected to prevent anybody to use it directly
    bar = source + foo();
}
public A(){
    super("Sub: ");
}
System.out.println(new A().bar);
System.out.println(new B().bar);
System.out.println(new A().bar);
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