Re: A basic question about constants

John B. Matthews a écrit : 
In article <42e1fbdb$0$29943$636a15ce@xxxxxxxxxxxx>,
 Richard <grin@xxxxxxxx> wrote:


Hello,

An extract from the javadoc of javax.sql.rowset.CachedRowSet (an interface):
---
COMMIT_ON_ACCEPT_CHANGES

static final boolean COMMIT_ON_ACCEPT_CHANGES

Causes the CachedRowSet object's SyncProvider to commit the changes when acceptChanges() is called. If set to false, the changes will not be committed until one of the CachedRowSet interface transaction methods is called.

See Also:
   commit(), rollback(), Constant Field Values
---

My basic question is: how is it possible to change the value of a constant defined in an interface?

Thanks in advance for your answers.

Richard


AFAIK, you can't: "Every field declaration in the body of an interface is implicitly public, static, and final." [§9.3] The value is set by the implementation so you'll know how to handle commits:

But how can the implementation set the value of the constant? It is not possible to change the value of a constant and the constant must be initialized in the interface.

For example,

public interface I {
  boolean constant = false;
}

public class AClass implements I {
  static {
    constant = true;
  }

  public boolean getConstant() {
    return constant;
  }
}

does not compile :
javac AClass.java
AClass.java:3: cannot assign a value to final variable constant
    constant = true;

There is certainly a thing that I have not understood...

Regards,

Richard


"Note: The acceptChanges() method will determine if the COMMIT_ON_ACCEPT_CHANGES is set to true or not. If it is set to true, all updates in the synchronization are committed to the data source. Otherwise, the application _must_ explicit[l]y call the commit() or rollback() methods as appropriate." [J2SE 1.5 API]


.

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