设计模式笔记（一）

设计模式笔记（一）

建立一个独立的对象池管理员,内部私有类指向管理对象，用PoolItem对象封装的目的是打上inUse指示。接口方法有入池、读取和出池。

 //: singleton:PoolManager.java    package singleton;         import java.util.*;         public class PoolManager {            private static class PoolItem {                    boolean inUse = false;                    Object item;                         PoolItem(Object item) {                            this.item = item;                    }            }                 private ArrayList items = new ArrayList();                 public void add(Object item) {                    items.add(new PoolItem(item));            }                 static class EmptyPoolException extends Exception {            }                 public Object get() throws EmptyPoolException {                    for (int i = 0; i < items.size(); i++) {                            PoolItem pitem = (PoolItem) items.get(i);                            if (pitem.inUse == false) {                                    pitem.inUse = true;                                    return pitem.item;                            }                    }                    // Fail early:                    throw new EmptyPoolException();                    // return null; // Delayed failure            }                 public void release(Object item) {                    for (int i = 0; i < items.size(); i++) {                            PoolItem pitem = (PoolItem) items.get(i);                            if (item == pitem.item) {                                    pitem.inUse = false;                                    return;                            }                    }                    throw new RuntimeException(item + " not found");            }    } // /:~

尽管对象池管理员不使用单例模式，但是子类连接池管理员是单例的。我认为这里使用了Adapter设计模式，接口做了映射。连接池管理员继承了对象池管理员，但并没有屏蔽父类的方法。

//: singleton:ConnectionPoolDemo.javapackage singleton;import junit.framework.*;interface Connection {Object get();void set(Object x);}class ConnectionImplementation implements Connection {public Object get() {return null;}public void set(Object s) {}}class ConnectionPool { // A singletonprivate static PoolManager pool = new PoolManager();public static void addConnections(int number) {for (int i = 0; i < number; i++)pool.add(new ConnectionImplementation());}public static Connection getConnection()throws PoolManager.EmptyPoolException {return (Connection) pool.get();}public static void releaseConnection(Connection c) {pool.release(c);}}public class ConnectionPoolDemo extends TestCase {static {ConnectionPool.addConnections(5);}public void test() {Connection c = null;try {c = ConnectionPool.getConnection();} catch (PoolManager.EmptyPoolException e) {throw new RuntimeException(e);}c.set(new Object());c.get();ConnectionPool.releaseConnection(c);}public void test2() {Connection c = null;try {c = ConnectionPool.getConnection();} catch (PoolManager.EmptyPoolException e) {throw new RuntimeException(e);}c.set(new Object());c.get();ConnectionPool.releaseConnection(c);}public static void main(String args[]) {junit.textui.TestRunner.run(ConnectionPoolDemo.class);}} // /:~