strategy

Strategy Design Pattern

• A class behavior or its algorithm can be changed at run time.

• Creating objects which represent various strategies and a context object whose behavior varies as per its strategy object. The strategy object changes the executing algorithm of the context object.

• The Strategy pattern is to be used where we want to choose the algorithm to use at runtime. A good use of the Strategy pattern would be saving files in different formats, running various sorting algorithms, or file compression.

Example

ZipCompressionStrategy and RarCompressionStrategy both implements CompressionStrategy interface.

A CompressionContext will run the common way to create based on strategy.

Remarks

• Strategy (CompressionStrategy) - defines an interface common to all supported algorithms. Context uses this interface to call the algorithm defined by a ConcreteStrategy.

• ConcreteStrategy (ZipCompressionStrategy and RarCompressionStrategy) - each concrete strategy implements an algorithm.

• Context (CompressionContext) - contains a reference to a strategy object.

Test

// For checking printing value
final ByteArrayOutputStream outputStreamCaptor = new ByteArrayOutputStream();
System.setOut(new PrintStream(outputStreamCaptor));

// test data
File file = new File("/test.txt");

CompressionContext context  = new CompressionContext();
context.setCompressionStrategy(new ZipCompressionStrategy());
context.createArchive(Arrays.asList(file));

// test result
Assertions.assertEquals("Compress files to ZIP", outputStreamCaptor.toString()
                .trim());