FileDataComputer

public interface FileDataComputer<T>

Interface specifying a method to compute derived data from files.

Instances of this interface can be used to derive data based on a content of a file. This is mainly used to share derived data with other tasks in the build execution, and therefore resulting in less overall computation.

There can be scenarios where multiple tasks use the same files, and they derive the same data from them while converting it to a third representation. In this case it can be beneficial to only compute the intermediate representation once, and have it cached for re-use.

Example:
Some tasks have a JSON file as their inputs. A common step in these tasks is to parse the input JSON, and do their work based on that. As multiple tasks will need to parse this JSON, it can result in redundant computation of the same data. This is were this interface comes in, which can be used to parse the JSON only once, and have multiple tasks use this representation.

The execution context provides this service via the TaskContext.computeFileContentData(SakerFile, FileDataComputer<T>) function.

Implementations should adhere to the equals(Object) and hashCode() contract.

Implementations should implement the Externalizable for proper serialization if needed. (Generally, instances of this interface will not be persisted, but it should be serializable in order to ensure remote execution compatibility.)

Results of the computation should be serializable, preferably Externalizable.

TThe type of data this computer returns.

Methods

public T	compute(SakerFile file) Computes the data based on the contents of the parameter file.
public boolean	equals(Object obj) Checks if this data computer would compute the same data as the parameter given the same circumstances.
public int	hashCode() Returns a hash code value for the object.

public abstract T compute(SakerFile file) throws IOException

Computes the data based on the contents of the parameter file.

If the returned value of the function is null, the computation handler may throw a NullPointerException.

fileThe file to get the contents from for the computation.

The computed data.

IOExceptionIn case of I/O error.

public abstract boolean equals(Object obj)

Checks if this data computer would compute the same data as the parameter given the same circumstances.

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.

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

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)