策略模式

public class ProcessFiles {
  public interface Strategy {
    void process(File file);
  }
  private Strategy strategy;
  private String ext;
  public ProcessFiles(Strategy strategy, String ext) {
    this.strategy = strategy;
    this.ext = ext;
  }
  public void start(String[] args) {
    try {
      if(args.length == 0)
        processDirectoryTree(new File("."));
      else
        for(String arg : args) {
          File fileArg = new File(arg);
          if(fileArg.isDirectory())
            processDirectoryTree(fileArg);
          else {
            // Allow user to leave off extension:
            if(!arg.endsWith("." + ext))
              arg += "." + ext;
            strategy.process(
              new File(arg).getCanonicalFile());
          }
        }
    } catch(IOException e) {
      throw new RuntimeException(e);
    }
  }
  public void
  processDirectoryTree(File root) throws IOException {
    for(File file : Directory.walk(
        root.getAbsolutePath(), ".*\\." + ext))
      strategy.process(file.getCanonicalFile());
  }

 
}

注意策略模式和函数对象之间的关系，方法中的一个参数是函数对象，在方法中的策略使用了此函数对象中的函数，例如比较器comparator

public int sort(int[]a, comparator) {  ...;comparator.compare(a,b); }