设计模式(1)
设计模式(1)
jit-hakase 发表于4个月前
设计模式(1)
  • 发表于 4个月前
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摘要: 创建型

#设计模式 使用设计模式的原则

  1. 开闭原则(Open Close Principle) 说对扩展开放, 对修改关闭, 在程序需要进行拓展的时候, 不能去修改原有的代码.
  2. 里氏代换原则(Liskov Substitution Principle) 任何基类可以出现的地方, 子类一定可以出现, 只有当衍生类可以替换掉基类, 软件单位的功能不受到影响时, 基类才能真正被复用, 而衍生类也能够在基类的基础上增加新的行为.
  3. 依赖倒转原则(Dependence Inversion Principle) 开闭原则的基础, 针对接口编程, 依赖于抽象而不依赖于具体.
  4. 接口隔离原则(Interface Segregation Principle) 使用多个隔离的接口, 优于使用单个接口, 可以降低类之间的耦合度.
  5. 迪米特法则(Demeter Principle) 又称最少知道原则, 一个实体应当尽量少的与其他实体之间发生相互作用, 使得系统功能模块相对独立.
  6. 合成复用原则(Composite Reuse Principle) 尽量使用合成和聚合的方式, 而不是使用继承.

##创建型模式 ###工厂模式 轻松方便地构造对象实例, 而不必关心构造对象实例的细节和复杂过程.

工厂模式分为工厂方法模式抽象工厂模式

####工厂方法模式(Factory Method)

利用工厂方法模式设计水果工厂

package javatest1;

interface Fruit {
	String getName();
}

class Apple implements Fruit {
	@Override
	public String getName() {
		return "apple";
	}
}

class Banana implements Fruit {
	@Override
	public String getName() {
		return "banana";
	}
}

class FruitFactory {

	public static Apple createApple() {
		return new Apple();
	}

	public static Banana createBanana() {
		return new Banana();
	}
}

public class Main {

	public static void main(String[] args) {

		Fruit apple = FruitFactory.createApple();
		Fruit banana = FruitFactory.createBanana();
		
		System.out.println(apple.getName());
		System.out.println(banana.getName());
	}
}

####抽象工厂模式(Abstract Factory)

利用抽象工厂模式设计水果工厂

package javatest1;

interface Fruit {
	String getName();
}

class Apple implements Fruit {
	@Override
	public String getName() {
		return "apple";
	}
}

class Banana implements Fruit {
	@Override
	public String getName() {
		return "banana";
	}
}

interface FruitFactory {
	Fruit create();
}

class AppleFactory implements FruitFactory {
	@Override
	public Apple create() {
		return new Apple();
	}
}

class BananaFactory implements FruitFactory {
	@Override
	public Banana create() {
		return new Banana();
	}
}

public class Main {

	public static void main(String[] args) {

		FruitFactory appleFactory = new AppleFactory();
		FruitFactory bananaFactory = new BananaFactory();
		
		Fruit apple = appleFactory.create();
		Fruit banana = bananaFactory.create();
		
		System.out.println(apple.getName());
		System.out.println(banana.getName());
	}
}

###单例模式(Singleton) 总有一些类的对象需要是唯一的, 这时可以考虑使用单例模式. 单例模式的优点: 严格控制对象的数目, 访问方式和封装.

地球单例模式

class Earth {

	private static Earth earth = new Earth();
	
	private Earth() {}
	
	public static Earth getInstance() {
		return earth;
	}
}

public class Main {

	public static void main(String[] args) {

		Earth foo = Earth.getInstance();
		Earth bar = Earth.getInstance();
		
		if (foo == bar) {
			System.out.println("Singleton");
		}
	}
}

###建造者模式(Builder)

将复杂对象的创建工作分解成方法, 通常可以设计成连缀方法, 最后返回构造完的对象.

使用建造者模式来建造水果盒子

import java.util.ArrayList;
import java.util.List;

interface Fruit {
	String getName();
}

class Apple implements Fruit {
	@Override
	public String getName() {
		return "apple";
	}
}

class Banana implements Fruit {
	@Override
	public String getName() {
		return "banana";
	}
}

class FruitBox {

	private List<Fruit> fruitList = new ArrayList<>();
	
	public void add(Fruit fruit) {
		fruitList.add(fruit);
	}

	public List<Fruit> getFruitList() {
		return fruitList;
	}
}

class FruitBoxBuilder {

	private FruitBox fruitBox = new FruitBox();
	
	public FruitBoxBuilder append(Fruit fruit) {
		fruitBox.add(fruit);
		return this;
	}

	public List<Fruit> toList() {
		return fruitBox.getFruitList();
	}
}

public class Main {

	public static void main(String[] args) {

		Fruit apple = new Apple();
		Fruit banana = new Banana();
		
		FruitBoxBuilder builder = new FruitBoxBuilder();
		List<Fruit> fruitList = builder.append(apple).append(banana).toList();
		
		for (Fruit fruit : fruitList) {
			System.out.println(fruit.getName());
		}
	}
}

类库中使用建造者模式的StringBuilder

public class Main {

	public static void main(String[] args) {

		StringBuilder sb = new StringBuilder();
		String result = sb.append("hello").append(" java !").toString();

		System.out.println(result);
	}
}

###原型模式(Prototype) 原型模式可以使用预定义的原型对象来快速完成对象的创建

使用原型模式来创建颜色对象

import java.util.HashMap;
import java.util.Map;

interface ColorPrototype {
	void display();
}

class Color implements ColorPrototype {

	private int red, green, blue;
	
	public Color(Color color) {
		this.red = color.red;
		this.green = color.green;
		this.blue = color.blue;
	}
	
	public Color(int red, int green, int blue) {
		this.red = red;
		this.green = green;
		this.blue = blue;
	}
	
	@Override
	public void display() {
		String rgb = "RGB(" + this.red + ", " + this.green +
				", " + this.blue + ")";
		System.out.println(rgb);
	}
	
	public int getRed() { return red; }
	public void setRed(int red) { this.red = red; }
	public int getGreen() { return green; }
	public void setGreen(int green) { this.green = green; }
	public int getBlue() { return blue; }
	public void setBlue(int blue) { this.blue = blue; }
}

class ColorManager {
	
	Map<String, Color> colors = new HashMap<>();
	
	public void addPrototype(String key, Color color) {
		colors.put(key, color);
	}
	
	public Color getPrototype(String key) {
		
		Color color = colors.get(key);
		Color colorCopy = new Color(color);
		
		return colorCopy;
	}
}

public class Main {
	
	public static void main(String[] args) {
		
		ColorManager colorManager = new ColorManager();
		
		colorManager.addPrototype("red", new Color(255, 0, 0));
		colorManager.addPrototype("green", new Color(0, 255, 0));
		colorManager.addPrototype("blue", new Color(0, 0, 255));
		
		Color colorYellow = colorManager.getPrototype("red");
		colorYellow.setGreen(255);
		colorYellow.display();
	}
}
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