Java组合模式-apache commons-io
组合模式
关于组合模式的定义百度百科 比我解释详细的多。百度组合模式：http://baike.baidu.com/view/3591789.htm
这里我说一下我自己的体会：
[整体和部分都有一个公共的借口]
[整体的组成都是由部分组成，整体也有公共接口关于业务方法的实现，但是整体的实现方式一般和部分实现的方式不一样。]
[整体一般实现了对部分的管理，i.e. add & remove等，但是我认为不是一定需要]
在apache commons-io中子包 org.apache.commons.io.comparator 有一处组合模式的例子：
公共接口：AbstractFileComparator 这里准确的说是Comparator。但是在comparator包所有的类都从AbstractFileComparator继承得来。AbstractFileComparator不对外开放，准确说不是公共接口。
package org.apache.commons.io.comparator;import java.io.File;import java.util.Arrays;import java.util.Collections;import java.util.Comparator;import java.util.List;/*公共的接口的方法是Comparator的campare(arg1,arg2)*/abstract class AbstractFileComparator implements Comparator<File> { public File[] sort(File... files) { if (files != null) { Arrays.sort(files, this); } return files; } public List<File> sort(List<File> files) { if (files != null) { Collections.sort(files, this); } return files; } @Override public String toString() { return getClass().getSimpleName(); }}/*部分都实现了Comparator的compare方法只是实现的方法不一样这里只给出DefaultFileComparator的实现方式*//** * Compare the two files using the {@link File#compareTo(File)} method. * * @param file1 The first file to compare * @param file2 The second file to compare * @return the result of calling file1's * {@link File#compareTo(File)} with file2 as the parameter. */ public int compare(File file1, File file2) { return file1.compareTo(file2); }/*整体也需要实现compare方法，这里使用了部分的compare的具体的实现*//** * Compare the two files using delegate comparators. * * @param file1 The first file to compare * @param file2 The second file to compare * @return the first non-zero result returned from * the delegate comparators or zero. */ public int compare(File file1, File file2) { int result = 0; for (Comparator<File> delegate : delegates) { result = delegate.compare(file1, file2); if (result != 0) { break; } } return result; }/*整体需要有个接口来组合部分，在这个类的构造方法中有体现*/private static final Comparator<?>[] NO_COMPARATORS = {}; private final Comparator<File>[] delegates; /** * Create a composite comparator for the set of delegate comparators. * * @param delegates The delegate file comparators */ @SuppressWarnings("unchecked") // casts 1 & 2 must be OK because types are already correct public CompositeFileComparator(Comparator<File>... delegates) { if (delegates == null) { this.delegates = (Comparator<File>[]) NO_COMPARATORS;//1 } else { this.delegates = (Comparator<File>[]) new Comparator<?>[delegates.length];//2 System.arraycopy(delegates, 0, this.delegates, 0, delegates.length); } } /** * Create a composite comparator for the set of delegate comparators. * * @param delegates The delegate file comparators */ @SuppressWarnings("unchecked") // casts 1 & 2 must be OK because types are already correct public CompositeFileComparator(Iterable<Comparator<File>> delegates) { if (delegates == null) { this.delegates = (Comparator<File>[]) NO_COMPARATORS; //1 } else { List<Comparator<File>> list = new ArrayList<Comparator<File>>(); for (Comparator<File> comparator : delegates) { list.add(comparator); } this.delegates = (Comparator<File>[]) list.toArray(new Comparator<?>[list.size()]); //2 } }