TaskOutputChangeDetector

public interface TaskOutputChangeDetector

EqualityTaskOutputChangeDetector, StringValueTaskOutputChangeDetector

Strategy interface for detecting changes related to task outputs.

Implementations detect changes between two different task outputs in relation to the used data of them.

This interface is used to determine during incremental builds if a task needs to be rerun based on its input tasks.
If a task A depends on task B and a change detector was specified previously, then it will be invoked to detect any changes between different outputs of the input task B.

Tasks which have their input tasks' outputs changed will be rerun in case of incremental builds.

This interface can be used to partially depend on tasks which can significantly improve build performance.

Example:
Task A depends on task B.
Task B returns a complex output with fields named X and Y.
Task A only utilizes the value of the field Y to properly execute. In this case task A can specify a change detector which compares the expected Y value to the current one specified by the isChanged(Object) parameter.
If task B is rerun, and the field Y does not change, then task A will not be rerun, as its input task B is not considered to be changed in relation to task A.

It is strongly recommended that implementations implement the Externalizable interface.
It is recommended that implementations implement hashCode() and equals(Object).

EqualityTaskOutputChangeDetector

CommonTaskOutputChangeDetector

Methods

public boolean	equals(Object obj) Indicates whether some other object is "equal to" this one.
public int	hashCode() Returns a hash code value for the object.
public boolean	isChanged(Object taskoutput) Checks if the parameter task output should be considered as changed.

public abstract boolean equals(Object obj)

Overridden from: Object

Indicates whether some other object is "equal to" this one.

The equals method implements an equivalence relation on non-null object references:

It is reflexive: for any non-null reference value x, x.equals(x) should return true.
It is symmetric: for any non-null reference values x and y, x.equals(y) should return true if and only if y.equals(x) returns true.
It is transitive: for any non-null reference values x, y, and z, if x.equals(y) returns true and y.equals(z) returns true, then x.equals(z) should return true.
It is consistent: for any non-null reference values x and y, multiple invocations of x.equals(y) consistently return true or consistently return false, provided no information used in equals comparisons on the objects is modified.
For any non-null reference value x, x.equals(null) should return false.

The equals method for class Object implements the most discriminating possible equivalence relation on objects; that is, for any non-null reference values x and y, this method returns true if and only if x and y refer to the same object (x == y has the value true).

Note that it is generally necessary to override the hashCode method whenever this method is overridden, so as to maintain the general contract for the hashCode method, which states that equal objects must have equal hash codes.

objthe reference object with which to compare.

true if this object is the same as the obj argument; false otherwise.

Object.hashCode()

HashMap

public abstract int hashCode()

Overridden from: Object

Returns a hash code value for the object. This method is supported for the benefit of hash tables such as those provided by HashMap.

The general contract of hashCode is:

Whenever it is invoked on the same object more than once during an execution of a Java application, the hashCode method must consistently return the same integer, provided no information used in equals comparisons on the object is modified. This integer need not remain consistent from one execution of an application to another execution of the same application.
If two objects are equal according to the equals(Object) method, then calling the hashCode method on each of the two objects must produce the same integer result.
It is not required that if two objects are unequal according to the Object.equals(Object) method, then calling the hashCode method on each of the two objects must produce distinct integer results. However, the programmer should be aware that producing distinct integer results for unequal objects may improve the performance of hash tables.

As much as is reasonably practical, the hashCode method defined by class Object does return distinct integers for distinct objects. (This is typically implemented by converting the internal address of the object into an integer, but this implementation technique is not required by the Java™ programming language.)

a hash code value for this object.

Object.equals(Object)

System.identityHashCode(Object)

public abstract boolean isChanged(Object taskoutput)

Checks if the parameter task output should be considered as changed.

If this methods throws a RuntimeException then it is an implementation error, however the caller can interpret it as if it returned true.

taskoutputThe task output to detect changes on.

true if it is considered to be changed.