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## java.security
Interface DomainCombiner

All Known Implementing Classes:
  SubjectDomainCombiner

public interface DomainCombiner

A `DomainCombiner` provides a means to dynamically update the ProtectionDomains associated with the current `AccessControlContext`.

A `DomainCombiner` is passed as a parameter to the appropriate constructor for `AccessControlContext`. The newly constructed context is then passed to the `AccessController.doPrivileged(..., context)` method to bind the provided context (and associated `DomainCombiner`) with the current execution Thread. Subsequent calls to `AccessController.getContext` or `AccessController.checkPermission` cause the `DomainCombiner.combine` to get invoked.

The combine method takes two arguments. The first argument represents an array of ProtectionDomains from the current execution Thread, since the most recent call to `AccessController.doPrivileged`. If no call to doPrivileged was made, then the first argument will contain all the ProtectionDomains from the current execution Thread. The second argument represents an array of inherited ProtectionDomains, which may be `null`. ProtectionDomains may be inherited from a parent Thread, or from a privileged context. If no call to doPrivileged was made, then the second argument will contain the ProtectionDomains inherited from the parent Thread. If one or more calls to doPrivileged were made, and the most recent call was to doPrivileged(action, context), then the second argument will contain the ProtectionDomains from the privileged context. If the most recent call was to doPrivileged(action), then there is no privileged context, and the second argument will be `null`.

The `combine` method investigates the two input arrays of ProtectionDomains and returns a single array containing the updated ProtectionDomains. In the simplest case, the `combine` method merges the two stacks into one. In more complex cases, the `combine` method returns a modified stack of ProtectionDomains. The modification may have added new ProtectionDomains, removed certain ProtectionDomains, or simply updated existing ProtectionDomains. Re-ordering and other optimizations to the ProtectionDomains are also permitted. Typically the `combine` method bases its updates on the information encapsulated in the `DomainCombiner`.

After the `AccessController.getContext` method receives the combined stack of ProtectionDomains back from the `DomainCombiner`, it returns a new AccessControlContext that has both the combined ProtectionDomains as well as the `DomainCombiner`.

See Also:
  `AccessController`, `AccessControlContext`

Method Summary
`ProtectionDomain[]` | `combine(ProtectionDomain[] currentDomains, ProtectionDomain[] assignedDomains)` Modify or update the provided ProtectionDomains.

Method Detail

### combine

    public ProtectionDomain[] combine(ProtectionDomain[] currentDomains,
                                      ProtectionDomain[] assignedDomains)

  Modify or update the provided ProtectionDomains. ProtectionDomains may be added to or removed from the given ProtectionDomains. The ProtectionDomains may be re-ordered. Individual ProtectionDomains may be may be modified (with a new set of Permissions, for example).

  Parameters:
    `currentDomains` - the ProtectionDomains associated with the current execution Thread, up to the most recent privileged `ProtectionDomain`. The ProtectionDomains are are listed in order of execution, with the most recently executing `ProtectionDomain` residing at the beginning of the array. This parameter may be `null` if the current execution Thread has no associated ProtectionDomains.

    `assignedDomains` - an array of inherited ProtectionDomains. ProtectionDomains may be inherited from a parent Thread, or from a privileged `AccessControlContext`. This parameter may be `null` if there are no inherited ProtectionDomains.
  Returns:
    a new array consisting of the updated ProtectionDomains, or `null`.

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