# Compatibility report

Given the very large user base of SLF4J, we take backward compatibility very seriously. As such, changes that may cause incompatibility problems are listed in this page. Moreover, since slf4j-api.jar is the main entry point into SLF4J, that is the module that will be covered in most detail.

Please note that in many cases incompatibility problems are caused by mixing different versions of slf4j artifacts. For example, if you are using slf4j-api-1.5.4.jar you should also use slf4j-simple-1.5.4.jar, using slf4j-simple-1.4.2.jar will not work. The same goes for all other SLF4J artifacts.

The list is computed using clirr. If you have reasons to suspect incompatible changes not mentioned here, please kindly contact the slf4j developers list.

## Version 1.5.7 compared to 1.5.6

No breaking changes to report.

## Version 1.5.6 compared to 1.5.5

Severity | Description | Class | Method / Field
--- | --- | --- | ---
Error | The number of parameters of SubstituteLoggerFactory constructor has changed | org.slf4j.helpers.SubstituteLoggerFactory | public SubstituteLoggerFactory(java.util.List)

The `SubstituteLoggerFactory` class is used internally by the LoggerFactory class. Changes to the constructor of SubstituteLoggerFactory should have strictly no effect on users.

## Version 1.5.5 compared to 1.5.4

No breaking changes to report.

## Version 1.5.4 compared to 1.5.3

### slf4j-api module, list of breaking changes:

Severity | Description | Class | Method / Field
--- | --- | --- | ---
Error | Method 'hasReferences()' has been added to an interface | org.slf4j.Marker | public boolean hasReferences()
Info | Method 'hasChildren()' was deprecated | org.slf4j.Marker | public boolean hasChildren()

The `hasChildren()` and other documentation in the Marker interface was misleading users to think in terms of parent child relationship for markers. However, as bug 100 illustrates, associating markers as parents and children is not very helpful. It is much better to think of markers in terms of abstract graphs. As such, we now say that a marker contains (zero or more) `references` to other markers.

This breaking change is justified because it corrects a conceptual error in the design. Previously, it was all too easy for developers to get confused and incorrectly link markers together.

## Version 1.5.3 compared to 1.5.2

### slf4j-api module, list of breaking changes:

Severity | Description | Class | Method / Field
--- | --- | --- | ---
Error | Added final modifier to class | org.slf4j.helpers.MessageFormatter |

Declaring `MessageFormatter` class as final should not affect users, unless they extend this class. However, since this class is intended to be used internally, very few users should be affected.

## Version 1.5.2 compared to 1.5.1

No breaking changes to report.

## Version 1.5.1 compared to 1.5.0

### slf4j-api module, list of breaking changes:

Severity | Description | Class | Method / Field
--- | --- | --- | ---
Error | Method 'getCopyOfContextMap()' has been added to an interface | org.slf4j.spi.MDCAdapter | public java.util.Map getCopyOfContextMap()
Error | Method 'setContextMap(Map)' has been added to an interface | org.slf4j.spi.MDCAdapter | public void setContextMap(java.util.Map)
Error | Method 'getDetachedMarker(String)' has been added to an interface | org.slf4j.IMarkerFactory | public org.slf4j.Marker getDetachedMarker(java.lang.String)
Info | Method 'equals(Object)' has been added to an interface | org.slf4j.Marker | public boolean equals(java.lang.Object)
info | Method 'hashCode()' has been added to an interface | org.slf4j.Marker | public int hashCode()

The addition of the `getCopyOfContextMap()` method in the `MDCAdapter` class should only impact users who have their own implementation of the said interface. Except for bindings that ship with SLF4J and for logback-classic, which will be naturally upgraded, there are no known other implementations of `MDCAdapter`. In a rare but still possible scenario, if the user mixes different versions for slf4j-api.jar, say version 1.5.1. and an SLF4J binding, say slf4j-log4j12.jar version 1.5.0, then a `java.lang.AbstractMethodError` will be thrown, but only if the client code calls the newly added method. In short, although generally speaking the addition of a method to an interface is a breaking change, we are confident that no users will be impacted in this particular case.

Similar reasoning applies to the `setContextMap(Map)` method.

The addition of `getDetachedMarker(String)` method in the `org.slf4j.IMarkerFactory` should not impact users as the only (known) implementation of this interface ships with SLF4J itself.

The `equals()` and `hashCode()` methods were added to the `org.slf4j.Marker` interface for documentation purposes. Given that all objects implicitly implement these methods, their addition should theoretically not break existing code.

### Other modules

No breaking changes to report.

## Version 1.5.0 compared to 1.4.3

No breaking changes to report.

## Version 1.4.3 compared to 1.4.2

No breaking changes to report.

## Version 1.4.2 compared to 1.4.1

No breaking changes to report.

## Version 1.4.1 compared to 1.4.0

No breaking changes to report.