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Behavioral Patterns  «Prev  Next»

Strategy Pattern Code in Java

The following is an example of a file compression tool where a zip or rar file is created.
The Strategy interface is defined first:

package com.java.behavioral.strategy;
//Strategy Interface
public interface CompressionStrategy{
  public void compressFiles(ArrayList files);
}

Two implementations are provided,
  1. one for zip and
  2. one for rar

package com.java.behavioral.strategy;
public class ZipCompressionStrategy implements CompressionStrategy{
 public void compressFiles(ArrayList<File> files){
 //using ZIP approach
 }
}

package com.java.behavioral.strategy;
public class RarCompressionStrategy 
 implements CompressionStrategy{
 public void compressFiles(ArrayList<File> files){
  //using RAR approach
 }
}


The context will provide a way for the client to compress the files.
Assume there is a preferences setting in our application that sets which compression algorithm to use.
We can change our strategy using the setCompressionStrategy method in the Context.

package com.java.behavioral.strategy;
public class CompressionContext{
 private CompressionStrategy str;
 //this can be set at runtime by the application preferences
 public void setCompressionStrategy(CompressionStrategy strat){
  this.str = strat;
 }
 //use the strategy
 public void createArchive(ArrayList<File> files){
  strategy.compressFiles(files);
 }
}

All the client has to do now is pass through the files to the CompressionContext

package com.java.behavioral.strategy;
public class Client{
 public static void main(String[] args){
  CompressionContext ctx = new CompressionContext();
  //we could assume context is already set by preferences
  ctx.setCompressionStrategy(new ZipCompressionStrategy());
  //get a list of files ...
  ctx.createArchive(fileList);
 }
}