# Interface CircuitBreaker<T>

Type Parameters:
  `T` - the type of the value monitored by this circuit breaker

All Known Implementing Classes:
  `AbstractCircuitBreaker, EventCountCircuitBreaker, ThresholdCircuitBreaker`

public interface CircuitBreaker<T>
An interface describing a Circuit Breaker component.

A circuit breaker can be used to protect an application against unreliable services or unexpected load. It typically monitors a specific resource. As long as this resource works as expected, it stays in state closed, meaning that the resource can be used. If problems are encountered when using the resource, the circuit breaker can switch into state open; then access to this resource is prohibited. Depending on a concrete implementation, it is possible that the circuit breaker switches back to state closed when the resource becomes available again.

This interface defines a generic protocol of a circuit breaker component. It should be sufficiently generic to be applied to multiple different use cases.

Since:
  3.5

- ## Method Summary

  Modifier and Type
  Method
  Description
  `boolean`
  `checkState()`
  Checks the state of this circuit breaker and changes it if necessary.
  `void`
  `close()`
  Closes this circuit breaker.
  `boolean`
  `incrementAndCheckState(T increment)`
  Increments the monitored value and performs a check of the current state of this circuit breaker.
  `boolean`
  `isClosed()`
  Tests the current closed state of this circuit breaker.
  `boolean`
  `isOpen()`
  Tests the current open state of this circuit breaker.
  `void`
  `open()`
  Opens this circuit breaker.

- ## Method Details

  - ### checkState

    boolean checkState()
    Checks the state of this circuit breaker and changes it if necessary. The return value indicates whether the circuit breaker is now in state closed; a value of true typically means that the current operation can continue.
    Returns:
      true if the circuit breaker is now closed; false otherwise.

  - ### close

    void close()
    Closes this circuit breaker. Its state is changed to closed. If this circuit breaker is already closed, this method has no effect.

  - ### incrementAndCheckState

    boolean incrementAndCheckState(T increment)
    Increments the monitored value and performs a check of the current state of this circuit breaker. This method works like `checkState()`, but the monitored value is incremented before the state check is performed.
    Parameters:
      `increment` - value to increment in the monitored value of the circuit breaker
    Returns:
      true if the circuit breaker is now closed; false otherwise

  - ### isClosed

    boolean isClosed()
    Tests the current closed state of this circuit breaker. A return value of true means that the circuit breaker is currently closed. This means that everything is okay with the monitored subsystem.
    Returns:
      the current closed state of this circuit breaker.

  - ### isOpen

    boolean isOpen()
    Tests the current open state of this circuit breaker. A return value of true means that the circuit breaker is currently open indicating a problem in the monitored subsystem.
    Returns:
      the current open state of this circuit breaker.

  - ### open

    void open()
    Opens this circuit breaker. Its state is changed to open. Depending on a concrete implementation, it may close itself again if the monitored subsystem becomes available. If this circuit breaker is already open, this method has no effect.