java开发中常用的几种设计模式及代码例子

1、单例模式是一种常用的软件设计模式，在它的核心结构中值包含一个被称为单例的特殊类。一个类只有一个实例，即一个类只有一个对象实例。package design.pattern;public class Singleton { private static Singleton singleton; private Singleton() {} public static Singleton getInstance() { if (singleton == null) { synchronized (Singleton.class) { singleton = new Singleton(); } } return singleton; }}

2、工厂模式根据需要返回我们的对象。应用比较熟悉的场景就是spring配置文件了。package design.pattern;public class MyFactory { public static final int TYPE_MI = 1;// 大米 public static final int TYPE_YU = 2;// 油 public static final int TYPE_SC = 3;// 蔬菜 public static Food getFoods(int foodType) { switch (foodType) { case TYPE_MI: return new DaMi(); case TYPE_YU: return new You(); case TYPE_SC: default: return new ShuCai(); } }}abstract class Food {}class DaMi extends Food {}class You extends Food {}class ShuCai extends Food {}

3、适配器模式 将一个类的接口转换成客户希望的另外一个接口。通俗地讲，就是在2个类之间做了一个衔接。比如你在调用A类的doSomething方法，实际上内部实现调用了B类的doSomething方法。package design.pattern;public class MyAdapter { private MyAdapterImpl adapterImpl; public MyAdapter(MyAdapterImpl myAdapterImpl) { this.adapterImpl = myAdapterImpl; } public void doSomething() { adapterImpl.doSomething(); } public static void main(String args[]) { new MyAdapter(new MyAdapterImpl()).doSomething(); }}class MyAdapterImpl { public void doSomething() { }}

4、代理模式它的定义是：代理模式给某一个对象提供一个代理对象，并由代理对象控制对原对象的引用。Java的反射机制，很多地方就用了代理模式来实现。package design.pattern;import java.lang.reflect.InvocationHandler;import java.lang.reflect.Method;import java.lang.reflect.Proxy;public class DynamicProxyMain { public static void main(String[] args) { Person smallPerson = new Child(); Person proxyBuyHouse = (Person) Proxy.newProxyInstance(Person.class.getClassLoader(), new Class[] { Person.class }, new DynamicProxyHandler(smallPerson)); proxyBuyHouse.eat(); }}interface Person { void eat();}class Child implements Person { @Override public void eat() { // 小孩吃什么 System.out.println("eating"); }}class DynamicProxyHandler implements InvocationHandler { private Object object; public DynamicProxyHandler(final Object object) { this.object = object; } @Override public Object invoke(Object proxy, Method method, Object[] args) throws Throwable { System.out.println("调用前日志监控"); Object result = method.invoke(object, args); System.out.println("调用后日志监控"); return result; }}

5、监听模式当事件源触发某种行为，会自动执行事件监听器里面相应的方法。Java监听模式右三个部分组成：事件源、事件对象、事件监听器。package design.pattern;public class ListenerTest { public static void main(String[] args) { MyListener myListener = new MyListener(); MyPerson person = new MyPerson(); person.addEatListener(myListener); person.eat(); }}//事件源class MyPerson{ private Listener listener;//监听器引用 //给事件源添加监听器 public void addEatListener(Listener listener) { this.listener = listener; } public void eat() { //吃了很多 if(listener != null) { Event event=new Event() ; event.setPerson(this); listener.isThinking(event);//监听吃饭时，想了什么 } } }//事件class Event { private MyPerson person;// 事件源的引用 public MyPerson getPerson() { return person; } public void setPerson(MyPerson person) { this.person = person; }}interface Listener { public void isThinking(Event event);}class MyListener implements Listener { @Override public void isThinking(Event event) { System.out.println(" is isThinking many things !"); }}

6、装饰器模式简单说就是不改变现有类的结构前提下，扩展它的功能。用别的类来增加原有类的功能。package design.pattern;public class MyDecorator { public static void main(String[] args) { Animal animal= new SmallDog(new Pet()); animal.eat(); }}interface Animal { public void eat();}class Pet implements Animal { @Override public void eat() { System.out.println("eat food"); }}class Dog implements Animal{ protected Animal animal; public Dog(Animal animal) { this.animal = animal; } @Override public void eat() { this.animal.eat(); } }class SmallDog extends Dog{ public SmallDog(Animal animal) { super(animal); } public void eat() { System.out.println("eat other food "); this.animal.eat(); }}