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<File> files);
}

Two implementations are provided,

one for zip and
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);
}
}