組合模式(Composite Pattern)是能夠使容器與内容具有一緻性,創造出遞歸結構的模式。
Entry.java
package com.test.dp.Composite.Sample;
//抽象類,表示“目錄條目”,用來實作File和Directory的一緻性
public abstract class Entry {
public abstract String getName(); // 擷取名字
public abstract int getSize(); // 擷取大小
public Entry add(Entry entry) throws FileTreatmentException { // 加入目錄條目
throw new FileTreatmentException();
}
public void printList() { // 為一覽加上字首并顯示目錄條目一覽
printList("");
}
protected abstract void printList(String prefix); // 為一覽加上字首
public String toString() { // 顯示代表類的文字
return getName() + " (" + getSize() + ")";
}
}
File.java
package com.test.dp.Composite.Sample;
//檔案類,代表“内容”
public class File extends Entry {
private String name;
private int size;
public File(String name, int size) {
this.name = name;
this.size = size;
}
public String getName() {
return name;
}
public int getSize() {
return size;
}
protected void printList(String prefix) {
System.out.println(prefix + "/" + this);
}
}
Directory.java
package com.test.dp.Composite.Sample;
import java.util.Iterator;
import java.util.ArrayList;
//檔案夾類,代表“目錄”
public class Directory extends Entry {
private String name; // 檔案夾的名字
private ArrayList directory = new ArrayList(); // 檔案夾中目錄條目的集合
public Directory(String name) { // 構造函數
this.name = name;
}
public String getName() { // 擷取名字
return name;
}
public int getSize() { // 擷取大小
int size = 0;
Iterator it = directory.iterator();
while (it.hasNext()) {
Entry entry = (Entry)it.next();
size += entry.getSize();
}
return size;
}
public Entry add(Entry entry) { // 增加目錄條目
directory.add(entry);
return this;
}
protected void printList(String prefix) { // 顯示目錄條目一覽
System.out.println(prefix + "/" + this);
Iterator it = directory.iterator();
while (it.hasNext()) {
Entry entry = (Entry)it.next();
entry.printList(prefix + "/" + name);
}
}
}
FileTreatmentException.java
package com.test.dp.Composite.Sample;
//表示向檔案中增加Entry時發生異常的類
public class FileTreatmentException extends RuntimeException {
public FileTreatmentException() {
}
public FileTreatmentException(String msg) {
super(msg);
}
}
Main.java
package com.test.dp.Composite.Sample;
public class Main {
public static void main(String[] args) {
try {
System.out.println("Making root entries...");
Directory rootdir = new Directory("root");
Directory bindir = new Directory("bin");
Directory tmpdir = new Directory("tmp");
Directory usrdir = new Directory("usr");
rootdir.add(bindir);
rootdir.add(tmpdir);
rootdir.add(usrdir);
bindir.add(new File("vi", 10000));
bindir.add(new File("latex", 20000));
rootdir.printList();
System.out.println("");
System.out.println("Making user entries...");
Directory yuki = new Directory("yuki");
Directory hanako = new Directory("hanako");
Directory tomura = new Directory("tomura");
usrdir.add(yuki);
usrdir.add(hanako);
usrdir.add(tomura);
yuki.add(new File("diary.html", 100));
yuki.add(new File("Composite.java", 200));
hanako.add(new File("memo.tex", 300));
tomura.add(new File("game.doc", 400));
tomura.add(new File("junk.mail", 500));
rootdir.printList();
} catch (FileTreatmentException e) {
e.printStackTrace();
}
}
}
執行結果:
Making root entries...
/root (30000)
/root/bin (30000)
/root/bin/vi (10000)
/root/bin/latex (20000)
/root/tmp (0)
/root/usr (0)
Making user entries...
/root (31500)
/root/bin (30000)
/root/bin/vi (10000)
/root/bin/latex (20000)
/root/tmp (0)
/root/usr (1500)
/root/usr/yuki (300)
/root/usr/yuki/diary.html (100)
/root/usr/yuki/Composite.java (200)
/root/usr/hanako (300)
/root/usr/hanako/memo.tex (300)
/root/usr/tomura (900)
/root/usr/tomura/game.doc (400)
/root/usr/tomura/junk.mail (500)
總結:
優點:1、高層子產品調用簡單。2、節點自由增加。
缺點:在使用組合模式時,其葉子和樹枝的聲明都是實作類,而不是接口,違反了依賴倒置原則。
使用場景:部分、整體場景,如樹形菜單,檔案、檔案夾的管理。
注意事項:定義時為具體類。